Make the DOM parser cheaper per container and per member (#5882)

* Reserve the parser's nesting stack once

The stack of open arrays and objects was a std::vector<std::uint8_t> that
allocated at the first push_back and then reallocated at 1, 2, 4, 8 bytes,
so a document nested four levels deep made four allocations before it
parsed a value. A document that starts with a container now reserves 32
levels in one allocation; deeper documents grow as before. The loop that
reads the tokens is the code it was, so large documents are not affected
(a stack object with its own storage, and a reserve at every container,
both cost the token loop instructions or cycles).

Fixed cost of parsing a 124-byte object (macOS instructions): accept
-7.6 %, DOM -2.5 %; no change for a single number.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Build arrays of the DOM parser in one exact-size allocation

Reading an array of unknown length appended its elements to a std::vector
one at a time, so a small array reallocated (and moved its elements) at
sizes 1, 2, 4, ... The DOM SAX parser now collects the elements of arrays
whose length is unknown on one stack shared by all open arrays and moves
them into an array of exactly the right size when the closing bracket
arrives. An array that grows past 16 elements switches to appending to its
own vector, so large arrays pay no second copy. Binary formats, which
announce the length, and builds with JSON_DIAGNOSTICS or
JSON_DIAGNOSTIC_POSITIONS (whose values need their final place from the
start) keep storing into the array directly.

The stacks of open containers are reserved on first use instead of growing
from one element.

The binary readers get a DOM parser of their own, json_sax_dom_binary_parser:
it is the plain parser that stores every value directly in its container
(the code the readers used before). Their containers announce their size, so
the bookkeeping of the collecting parser (frame entries, the destination of a
finished container) was pure overhead for them: with the collecting parser
FromBinaryShape nested was 3-12 % and containers up to 5 % more instructions
(GCC) than before. With the plain parser Linux Ir of FromBinaryShape and
FromBinaryBuffer is within 0.8 % of develop (Clang: identical).

canada.json has 56 000 two-element arrays that took three allocations each
and now take two. DOM parse Ir on Linux against develop (GCC / Clang): canada
-7.0 % / -7.7 %, citm -0.8 % / -1.6 %, 124-byte object -5.4 % / -5.5 %;
accept and SAX are untouched.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Reuse one value for the key events of the callback parser

parse() with a callback built a new string value for every key it passed to
the callback (a heap allocation and release per key), and copied the key a
second time into the object. The callback parser now keeps one string value
for key events, which it assigns, and moves the key into the object.

Callback parse, Linux Ir (GCC / Clang): twitter -13.3 % / -11.7 %, citm
-9.5 % / -7.6 %. (Earlier macOS measurement: twitter -19.5 % instructions.)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Remember where the DOM parser stores the next value

The DOM SAX parser looked up the innermost open container for every value:
the end of its frame stack, then the object or array pointer in the frame.
Compilers have to reload all of that after each value is stored, since a
store of a value may alias the frame. The parser now keeps the innermost
container's kind and, for an array that stores directly, the array itself
in members, updated when a container opens or closes.

Flat arrays of numbers are the case that mattered: parsing floats.json
(1 000 000 doubles) into a DOM took 2 % more cycles than before the
previous commit on macOS and now takes 0.4 % fewer than the code before it
(signed_ints.json -0.8 %). Linux Ir is unchanged (canada -6.1 % GCC /
-6.9 % Clang, citm -0.3 % / -0.8 %, twitter +0.2 % / 0.0 %).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Look up the keys of big ordered_json objects in a hash table

ordered_map keeps its elements in a vector and searches it linearly for
every key it adds, so parsing an object with n keys into ordered_json took
O(n^2) key comparisons: 33 billion instructions for one object with 30 000
keys, where json needs 245 million. From 64 keys on, the DOM parser now
keeps a hash table of the keys of the open object (hashes and positions
only; the elements stay in the vector) and finds duplicate keys there. The
result is the same, including the position of a key that occurs twice.
Smaller objects, std::map based objects and key types without std::hash
are untouched.

ordered_json parse, macOS instructions: object with 1 000 keys 64.8 M ->
14.6 M, 10 000 keys 5 104 M -> 38.7 M, 30 000 keys 33 358 M -> 89 M.
Linux Ir of an object with 2 000 keys: 43.0 M -> 1.9 M (GCC), 37.9 M ->
1.8 M (Clang).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Trim the work the DOM parser does per container and per member

Opening and closing an array or object cost the DOM parser more than before
the exact-size array change, which showed on documents of many small
objects (jeopardy.json: +1.4 % Ir with GCC). This takes it back:

- the stack of open containers keeps its first eight entries in the parser
  object instead of in a vector, so it needs no capacity check beyond the
  push itself and no allocation for typical documents;
- a container is created in the place it ends up in, instead of as a
  temporary that is then moved there;
- a new object member, which is null, is constructed over the null instead
  of being swapped with it (only with the default base class of basic_json);
- the key index that big ordered_json objects use is only a part of the
  stack entries of objects that can have one;
- an array that outgrows the stack reserves twice what it has so far, as a
  vector that grew by itself would have.

DOM parse Ir of the series up to here against develop, Linux GCC / Clang:
canada -6.6 % / -7.3 %, citm +1.2 % / +0.2 %, jeopardy +0.4 % / -0.1 %,
124-byte object -6.5 % / -6.2 %. (twitter measures +6.8 % / +6.6 % at this
point in steady state, almost all of it in glibc's malloc/consolidate for the
new allocation sizes; with the last commit of the series it is -0.1 % / 0.0 %.)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Test parsing containers of the sizes where the DOM parser changes storage

The DOM parser collects the elements of an array on a stack (up to 16) and
the members of an ordered_json object (up to 32) before it moves them into
the container, and uses a hash table for keys from 64 members on. Parse
arrays and objects of the sizes around these limits, nested into each other,
with repeated keys, and as random trees that are built next to their text,
and compare json and ordered_json against the value built through the API.

The tests pass on the code from before these changes as well. The random
trees are what finds the mistakes that are easy to make here: while the
collecting change was being written, a collected array that outgrew the
stack at the moment its parent had just reached the limit left its elements
in the parent, and only these tests (142 failed assertions) showed it.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Do not convert floats that cannot overflow in accept()

accept() only has to find out whether a float token is finite: json_sax_acceptor
ignores the value, and the parser rejects only a float that overflows. A
float whose digits fit into 19 digits and whose decimal exponent is at most
max_exponent10 - 19 is below 10^max_exponent10 and cannot overflow, so the
lexer, told by accept() that the value is not needed, skips the conversion
for those. A token that may overflow, with more digits, or in another float
format is converted as before, so 1e309 and its neighbours are rejected as
they were (the new test compares accept() with parse() on tokens around the
limit).

json::accept(): canada.json Ir -8.6 % (GCC) / -10.9 % (Clang), 124-byte
object -3.2 %; cycles on the M1 (release benchmarks, LTO): canada -7.8 %,
floats.json -9.0 %. The check tests the accept() flag first, so the parser
that needs the value pays one load and branch: SaxParse canada +0.35 % Ir
(GCC and Clang), DOM canada +0.4 %.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Collect the members of ordered_json objects on a stack until they are known

An ordered_json object keeps its members in a vector and appends every new
member to it, so reading an object of unknown size reallocated the vector at
1, 2, 4, 8, ... members, and ordered_map copies all keys on every
reallocation. The DOM SAX parser now collects the members of such objects on
one stack shared by all open objects, as it does the elements of arrays, and
moves them into a vector of exactly the right size when the closing brace
arrives. An object that gets past 32 members switches to appending to its
own vector (and, from 64, to the key index of the earlier commit). The
members are the same, in the same order, and a key that occurs twice keeps
the place of its first occurrence. std::map based objects, objects whose
size the input announces (binary formats), and builds with JSON_DIAGNOSTICS
or JSON_DIAGNOSTIC_POSITIONS are untouched.

What only ordered objects need (the collected members, the key indexes) is
a member of the parser only for them, and the code that stores a value tries
the array that takes its elements directly first. An array that outgrows
the stack now reserves 32 elements, the capacity a vector that grew by
itself has at that point; with the larger reserve before, parsing
floats.json (1 000 000 numbers) was 2 % slower on Apple M1 than before this
series.

ordered_json parse, Linux Ir against develop (GCC / Clang): citm -11.6 % /
-11.7 %, twitter -8.4 % / -8.4 %, jeopardy (12 000 objects of 7 keys)
-10.5 % / -8.0 %, canada -3.9 % / -5.2 %, 124-byte object -20.9 % / -16.5 %.
macOS time (M1, earlier base): citm -19 %, twitter -13 %, jeopardy -13 %,
canada -14 %, 124-byte object -26 %. json parse: steady-state twitter -0.1 %
(see the previous commits), citm -1.2 %.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Rename the key index's match callback so Flawfinder doesn't read it as std::equal

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Bind the parser test's strings by reference in the range-for loop

GCC and Clang 14 (-Wrange-loop-construct) reported the copy.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Collect container values only in basic_json's own parse functions

A json_sax_dom_parser that a user constructs (as in the sax_no_exception
example) must hold the values read before a parse error, as on develop:
its value is used after the error. The values of containers of unknown
size are now collected on a stack only with the new template parameter
Collect (default false), which json::parse() and the json_view
materialization set; without it, every value is stored in place as it
arrives. A test checks the values kept after an error for json and
ordered_json.

Also fixes the clang-tidy, cpplint and Infer findings: the frame stack
keeps its first frames in a std::array (left uninitialized) and the
others in a std::unique_ptr, auto for create<>(), NOLINT for member
initializers -Weffc++ needs, and an @infer-ignore for the nullptr that
place_container() does not use.

json::parse() and ordered_json::parse() instructions are unchanged
(Apple clang; twitter, citm, canada, jeopardy: -0.03 % to +0.25 %).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Clarify the DOM parser's collection stacks and rename reenter_enclosing_container()

Address review comments: explain why a closed container erases only the top
of the shared stack, set the payload before the type, rename the helper that
makes the enclosing container current again, and declare the parser's state
stack right before reserving it.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Export json_sax_dom_parser from the C++20 module for MSVC

MSVC needs the detail classes that basic_json befriends to be visible in
the module (#3970, as json_sax_dom_callback_parser); with its new
template parameter, json_sax_dom_parser failed in ci_module_cpp20
(C2039, not a member of nlohmann::detail).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Keep the overflow-limit numbers of the parser test in a std::vector

clang-tidy (cppcoreguidelines-avoid-c-arrays) rejected the C array.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix the clang-tidy findings of the ordered_json parser tests

The container sizes are a std::array, the expected text uses raw string
literals, the generator's arithmetic is in parentheses, auto for the
result of make<>(), and single characters are appended as characters.
clang-tidy now reports nothing on the lines the branch adds to
unit-ordered_json.cpp and unit-class_parser.cpp (apart from checks CI's
clang-tidy does not have).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json_view/at.md

@@ -80,7 +80,8 @@ None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics
    Objects with 128 or more members get a hash index of their keys while parsing, so that a lookup in them takes
    constant time on average.
 2. Linear in `idx`: elements are skipped one at a time from the first one, since they are not a fixed size in the
-   index (unlike `BasicJsonType`'s array, which is random-access).
+   index (unlike `BasicJsonType`'s array, which is random-access). Constant if no element of the array is an array
+   or object, since the elements are then adjacent in the index.
 3. Linear in the number of reference tokens of `ptr` and, for each token, in the number of members of the object at
    that level (as 1.) or the index into the array (as 2.).
 

docs/mkdocs/docs/api/basic_json_view/back.md

@@ -28,7 +28,8 @@ This exception does not carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.
 
 Linear in the size of the array or object: unlike [`front()`](front.md), which only ever looks at the first
 element, `back()` has to walk every element to find where they end, since elements are not a fixed size in the
-index.
+index. Constant if no element of the array is an array or object, since the elements are then adjacent
+in the index.
 
 ## Notes
 

docs/mkdocs/docs/api/basic_json_view/operator[].md

@@ -86,7 +86,8 @@ None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics
    Objects with 128 or more members get a hash index of their keys while parsing, so that a lookup in them takes
    constant time on average.
 2. Linear in `idx`: elements are skipped one at a time from the first one, since they are not a fixed size in the
-   index (unlike `BasicJsonType`'s array, which is random-access).
+   index (unlike `BasicJsonType`'s array, which is random-access). Constant if no element of the array is an array
+   or object, since the elements are then adjacent in the index.
 3. Linear in the number of reference tokens of `ptr` and, for each token, in the number of members of the object at
    that level (as 1.) or the index into the array (as 2.).
 

docs/mkdocs/scripts/mermaid/package-lock.json

@@ -1105,9 +1105,9 @@
       }
     },
     "node_modules/dompurify": {
-      "version": "3.4.16",
-      "resolved": "https://registry.npmjs.org/dompurify/-/dompurify-3.4.16.tgz",
-      "integrity": "sha512-sqo+pNp3qRhCIpbgRi1y8Tgk27Bo2Ry7w0dC1NBeNTdZChWjz9Xb/KOoZbRP/R6pQZ80Qw8YhXw13hWWBbMRnQ==",
+      "version": "3.4.17",
+      "resolved": "https://registry.npmjs.org/dompurify/-/dompurify-3.4.17.tgz",
+      "integrity": "sha512-B/pSlYVHQ58kqISD/yDjuJ1yfzI34m1gF4lAod2bwSRhiN4K5Cl3H8Af7hqB2PmTL911tdEudnnXn5FnhRoz0w==",
       "license": "(MPL-2.0 OR Apache-2.0)",
       "optionalDependencies": {
         "@types/trusted-types": "^2.0.7"

include/nlohmann/detail/conversions/from_json.hpp

@@ -69,10 +69,12 @@ void from_json(const BasicJsonType& j, std::optional<T>& opt)
 }
 #endif // JSON_HAS_CPP_17
 
-// read a number value of any of the three number types into val;
-// returns false (leaving val untouched) if j is not a number
-template<typename BasicJsonType, typename ArithmeticType>
-bool get_number_value(const BasicJsonType& j, ArithmeticType& val)
+// overloads for basic_json template parameters
+template < typename BasicJsonType, typename ArithmeticType,
+           enable_if_t < std::is_arithmetic<ArithmeticType>::value&&
+                         !std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
+                         int > = 0 >
+void get_arithmetic_value(const BasicJsonType& j, ArithmeticType& val)
 {
     switch (static_cast<value_t>(j))
     {
@@ -83,17 +85,17 @@ bool get_number_value(const BasicJsonType& j, ArithmeticType& val)
             const auto* ptr = j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>();
             JSON_ASSERT(ptr != nullptr);
             val = static_cast<ArithmeticType>(*ptr);
-            return true;
+            break;
         }
         case value_t::number_integer:
         {
             val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_integer_t*>());
-            return true;
+            break;
         }
         case value_t::number_float:
         {
             val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_float_t*>());
-            return true;
+            break;
         }
 
         case value_t::null:
@@ -104,19 +106,6 @@ bool get_number_value(const BasicJsonType& j, ArithmeticType& val)
         case value_t::binary:
         case value_t::discarded:
         default:
-            return false;
-    }
-}
-
-// overloads for basic_json template parameters
-template < typename BasicJsonType, typename ArithmeticType,
-           enable_if_t < std::is_arithmetic<ArithmeticType>::value&&
-                         !std::is_same<ArithmeticType, typename BasicJsonType::boolean_t>::value,
-                         int > = 0 >
-void get_arithmetic_value(const BasicJsonType& j, ArithmeticType& val)
-{
-    if (JSON_HEDLEY_UNLIKELY(!get_number_value(j, val)))
-    {
             throw_type_must_be("number", j);
     }
 }
@@ -267,18 +256,18 @@ auto from_json_array_impl(const BasicJsonType& j, std::array<T, N>& arr,
     }
 }
 
-// reserve() is called through this pair (used for arrays and objects alike)
-// so from_json_array_impl and the object from_json have a single body for both
-// containers that support reserve() and those that don't.
-template<typename ConstructibleContainerType>
-auto reserve_if_possible(ConstructibleContainerType& c, typename ConstructibleContainerType::size_type size, priority_tag<1> /*unused*/)
--> decltype(c.reserve(size), void())
+// reserve() is called through this pair (modeled on from_json_object_reserve)
+// so from_json_array_impl below has a single body for both ConstructibleArrayType
+// that support reserve() and those that don't.
+template<typename ConstructibleArrayType>
+auto from_json_array_reserve(ConstructibleArrayType& arr, typename ConstructibleArrayType::size_type size, priority_tag<1> /*unused*/)
+-> decltype(arr.reserve(size), void())
 {
-    c.reserve(size);
+    arr.reserve(size);
 }
 
-template<typename ConstructibleContainerType>
-void reserve_if_possible(ConstructibleContainerType& /*c*/, std::size_t /*size*/, priority_tag<0> /*unused*/)
+template<typename ConstructibleArrayType>
+void from_json_array_reserve(ConstructibleArrayType& /*arr*/, std::size_t /*size*/, priority_tag<0> /*unused*/)
 {}
 
 // append through push_back() where available; containers without it (such as
@@ -308,7 +297,7 @@ auto from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr, p
 {
     ConstructibleArrayType ret;
     const auto* inner_array = j.template get_ptr<const typename BasicJsonType::array_t*>();
-    reserve_if_possible(ret, inner_array->size(), priority_tag<1> {});
+    from_json_array_reserve(ret, inner_array->size(), priority_tag<1> {});
     for (const auto& elem : *inner_array)
     {
         // get<BasicJsonType>() returns *this, this won't call a from_json
@@ -389,6 +378,17 @@ inline void from_json(const BasicJsonType& j, CompatibleArrayType& bin)
     }
 }
 
+template<typename ConstructibleObjectType>
+auto from_json_object_reserve(ConstructibleObjectType& obj, typename ConstructibleObjectType::size_type size, priority_tag<1> /*unused*/)
+-> decltype(obj.reserve(size), void())
+{
+    obj.reserve(size);
+}
+
+template<typename ConstructibleObjectType>
+inline void from_json_object_reserve(ConstructibleObjectType& /*obj*/, std::size_t /*size*/, priority_tag<0> /*unused*/)
+{}
+
 // the keys of the source are sorted for the usual object types, so hinting the
 // end makes every insertion constant-time (for containers that order their keys
 // the same way); containers without emplace_hint() (such as ordered_map) fall
@@ -417,7 +417,7 @@ inline void from_json(const BasicJsonType& j, ConstructibleObjectType& obj)
 
     ConstructibleObjectType ret;
     const auto* inner_object = j.template get_ptr<const typename BasicJsonType::object_t*>();
-    reserve_if_possible(ret, inner_object->size(), priority_tag<1> {});
+    from_json_object_reserve(ret, inner_object->size(), priority_tag<1> {});
     for (const auto& p : *inner_object)
     {
         from_json_object_emplace(ret, p.first, p.second.template get<typename ConstructibleObjectType::mapped_type>(), priority_tag<1> {});
@@ -437,10 +437,6 @@ template < typename BasicJsonType, typename ArithmeticType,
                int > = 0 >
 inline void from_json(const BasicJsonType& j, ArithmeticType& val)
 {
-    // the number cases repeat get_number_value() on purpose: calling it here
-    // changes the inlining of get<T>() in the std::array conversion, which then
-    // runs 2.4x slower (GetArray benchmark, #5891); unlike get_arithmetic_value(),
-    // a boolean is accepted
     switch (static_cast<value_t>(j))
     {
         case value_t::number_unsigned:

include/nlohmann/detail/exceptions.hpp

@@ -66,7 +66,6 @@ enum class exception_id : int
     invalid_string_or_size = 113, ///< a binary input contains an invalid string or size specification
     bson_unsupported_type = 114, ///< a BSON record type is not supported
     invalid_high_precision_number = 115, ///< a UBJSON/BJData high-precision number cannot be parsed
-    invalid_document_image = 116, ///< json_document::load() rejects an image
     // invalid_iterator
     iterators_incompatible = 201, ///< the iterators of a range belong to different values
     iterator_from_other_value = 202, ///< an iterator does not belong to the value it is used with
@@ -101,8 +100,6 @@ enum class exception_id : int
     invalid_utf8 = 316, ///< dump() finds a string that is not valid UTF-8
     type_not_serializable = 317, ///< a value cannot be serialized to the requested binary format
     enum_key_duplicate = 318, ///< an enum-keyed map has two keys that serialize to the same string
-    document_binary_value = 319, ///< a binary value is stored in a json_document
-    document_image_unsupported = 320, ///< a json_document image cannot be saved or loaded (discarded document, big-endian target)
     discarded_value_used = 321, ///< a discarded value is used
     // out_of_range
     array_index_out_of_range = 401, ///< an array index is out of range
@@ -120,7 +117,6 @@ enum class exception_id : int
     patch_remove_parent_not_container = 413, ///< the parent of a JSON Patch 'remove' target is not a container
     patch_move_into_child = 414, ///< a JSON Patch 'move' moves a value into one of its children
     subtype_out_of_range = 415, ///< a binary subtype does not fit into one byte
-    document_too_large = 416, ///< a json_document input, its edit storage, or an image reaches the 32-bit (4 GiB) limit
     // other_error
     internal_error = 500, ///< unreachable code was reached
     patch_test_failed = 501, ///< a JSON Patch 'test' operation failed
@@ -150,13 +146,6 @@ class exception : public std::exception
         return concat("[json.exception.", ename, '.', std::to_string(id_), "] ");
     }
 
-    /// build the message "[json.exception.<ename>.<id>] <diagnostics><what_arg>"
-    template<typename BasicJsonContext>
-    static std::string what_impl(const std::string& ename, int id_, const std::string& what_arg, BasicJsonContext context)
-    {
-        return concat(name(ename, id_), diagnostics(context), what_arg);
-    }
-
     static std::string diagnostics(std::nullptr_t /*leaf_element*/)
     {
         return "";
@@ -169,21 +158,24 @@ class exception : public std::exception
         std::vector<std::string> tokens;
         for (const auto* current = leaf_element; current != nullptr && current->m_parent != nullptr; current = current->m_parent)
         {
-            const auto* parent = current->m_parent;
-            if (parent->is_array())
+            switch (current->m_parent->type())
             {
-                for (std::size_t i = 0; i < parent->m_data.m_value.array->size(); ++i)
+                case value_t::array:
                 {
-                    if (&parent->m_data.m_value.array->operator[](i) == current)
+                    for (std::size_t i = 0; i < current->m_parent->m_data.m_value.array->size(); ++i)
+                    {
+                        if (&current->m_parent->m_data.m_value.array->operator[](i) == current)
                         {
                             tokens.emplace_back(std::to_string(i));
                             break;
                         }
                     }
+                    break;
                 }
-            else if (parent->is_object())
+
+                case value_t::object:
                 {
-                for (const auto& element : *parent->m_data.m_value.object)
+                    for (const auto& element : *current->m_parent->m_data.m_value.object)
                     {
                         if (&element.second == current)
                         {
@@ -194,8 +186,20 @@ class exception : public std::exception
                             break;
                         }
                     }
+                    break;
+                }
+
+                case value_t::null: // LCOV_EXCL_LINE
+                case value_t::string: // LCOV_EXCL_LINE
+                case value_t::boolean: // LCOV_EXCL_LINE
+                case value_t::number_integer: // LCOV_EXCL_LINE
+                case value_t::number_unsigned: // LCOV_EXCL_LINE
+                case value_t::number_float: // LCOV_EXCL_LINE
+                case value_t::binary: // LCOV_EXCL_LINE
+                case value_t::discarded: // LCOV_EXCL_LINE
+                default:   // LCOV_EXCL_LINE
+                    break; // LCOV_EXCL_LINE
             }
-            // all other parent types (primitives) contribute no token
         }
 
         if (tokens.empty())
@@ -311,7 +315,7 @@ class invalid_iterator : public exception
     template<typename BasicJsonContext, enable_if_t<is_basic_json_context<BasicJsonContext>::value, int> = 0>
     static invalid_iterator create(int id_, const std::string& what_arg, BasicJsonContext context)
     {
-        const std::string w = exception::what_impl("invalid_iterator", id_, what_arg, context);
+        const std::string w = concat(exception::name("invalid_iterator", id_), exception::diagnostics(context), what_arg);
         return {id_, w.c_str()};
     }
 
@@ -335,7 +339,7 @@ class type_error : public exception
     template<typename BasicJsonContext, enable_if_t<is_basic_json_context<BasicJsonContext>::value, int> = 0>
     static type_error create(int id_, const std::string& what_arg, BasicJsonContext context)
     {
-        const std::string w = exception::what_impl("type_error", id_, what_arg, context);
+        const std::string w = concat(exception::name("type_error", id_), exception::diagnostics(context), what_arg);
         return {id_, w.c_str()};
     }
 
@@ -358,7 +362,7 @@ class out_of_range : public exception
     template<typename BasicJsonContext, enable_if_t<is_basic_json_context<BasicJsonContext>::value, int> = 0>
     static out_of_range create(int id_, const std::string& what_arg, BasicJsonContext context)
     {
-        const std::string w = exception::what_impl("out_of_range", id_, what_arg, context);
+        const std::string w = concat(exception::name("out_of_range", id_), exception::diagnostics(context), what_arg);
         return {id_, w.c_str()};
     }
 
@@ -381,7 +385,7 @@ class other_error : public exception
     template<typename BasicJsonContext, enable_if_t<is_basic_json_context<BasicJsonContext>::value, int> = 0>
     static other_error create(int id_, const std::string& what_arg, BasicJsonContext context)
     {
-        const std::string w = exception::what_impl("other_error", id_, what_arg, context);
+        const std::string w = concat(exception::name("other_error", id_), exception::diagnostics(context), what_arg);
         return {id_, w.c_str()};
     }
 

include/nlohmann/detail/input/binary_reader.hpp

@@ -86,7 +86,7 @@ JSON_INLINE_VARIABLE constexpr std::size_t max_valueless_container_size = 1 << 2
 /*!
 @brief deserialization of BJData, BON8, BSON, CBOR, MessagePack, and UBJSON values
 */
-template<typename BasicJsonType, typename InputAdapterType, typename SAX = json_sax_dom_parser<BasicJsonType, InputAdapterType>>
+template<typename BasicJsonType, typename InputAdapterType, typename SAX = json_sax_dom_binary_parser<BasicJsonType, InputAdapterType>>
 class binary_reader
 {
     using number_integer_t = typename BasicJsonType::number_integer_t;
@@ -293,40 +293,6 @@ class binary_reader
         return is_object ? sax->end_object() : sax->end_array();
     }
 
-    /*!
-    @brief close the innermost open container and report whether that
-           completed the value being read
-
-    The value begun by the driver is complete once its container is not
-    inside another one.
-
-    @param[out] value_complete  whether no container is left open
-    @return whether the SAX parser accepted the end event
-    */
-    bool leave_container_and_check(bool& value_complete)
-    {
-        if (JSON_HEDLEY_UNLIKELY(!leave_container()))
-        {
-            return false;
-        }
-        value_complete = container_stack.empty();
-        return true;
-    }
-
-    /*!
-    @brief read an object key and pass it to the SAX parser
-
-    @tparam GetKey  member function that reads the key into a string
-    @param[in,out] key  string the key is read into; cleared first
-    @return whether reading the key and the SAX event succeeded
-    */
-    template<bool (binary_reader::*GetKey)(string_t&)>
-    bool read_object_key(string_t& key)
-    {
-        key.clear();
-        return (this->*GetKey)(key) && sax->key(key);
-    }
-
     //////////
     // BSON //
     //////////
@@ -1098,34 +1064,6 @@ class binary_reader
         return last_byte_error(exception_id::invalid_string_or_size, concat("indefinite-length ", type_name, " is not allowed inside indefinite-length ", type_name, "; last byte: 0x", get_token_string()), context);
     }
 
-    /*!
-    @brief report an object key that is not a string
-
-    @param[in] found  description of what was found instead of a string key
-    @return false
-    */
-    bool unsupported_key_type(const char* found) const
-    {
-        return last_byte_error(exception_id::invalid_string_or_size, "only string keys are supported, but found ", "object key", found);
-    }
-
-    /*!
-    @brief read the length of a CBOR string or byte array and then its bytes
-
-    @tparam NumberType    the type of the length field
-    @tparam ContainerType the destination container (string_t or binary_t)
-    @param[in] context  further context information (for diagnostics)
-    @param[out] result  container the bytes are appended to
-
-    @return whether reading completed
-    */
-    template<typename NumberType, typename ContainerType>
-    bool get_cbor_sized_bytes(const char* context, ContainerType& result)
-    {
-        NumberType len{};
-        return get_number(len) && get_bytes(len, context, result);
-    }
-
     /*!
     @brief reads a definite-length CBOR string
 
@@ -1176,22 +1114,26 @@ class binary_reader
 
             case 0x78: // UTF-8 string (one-byte uint8_t for n follows)
             {
-                return get_cbor_sized_bytes<std::uint8_t>("string", result);
+                std::uint8_t len{};
+                return get_number(len) && get_string(len, result);
             }
 
             case 0x79: // UTF-8 string (two-byte uint16_t for n follow)
             {
-                return get_cbor_sized_bytes<std::uint16_t>("string", result);
+                std::uint16_t len{};
+                return get_number(len) && get_string(len, result);
             }
 
             case 0x7A: // UTF-8 string (four-byte uint32_t for n follow)
             {
-                return get_cbor_sized_bytes<std::uint32_t>("string", result);
+                std::uint32_t len{};
+                return get_number(len) && get_string(len, result);
             }
 
             case 0x7B: // UTF-8 string (eight-byte uint64_t for n follow)
             {
-                return get_cbor_sized_bytes<std::uint64_t>("string", result);
+                std::uint64_t len{};
+                return get_number(len) && get_string(len, result);
             }
 
             default:
@@ -1326,7 +1268,7 @@ class binary_reader
                 break;
         }
 
-        return unsupported_key_type(found);
+        return last_byte_error(exception_id::invalid_string_or_size, "only string keys are supported, but found ", "object key", found);
     }
 
     /*!
@@ -1379,22 +1321,30 @@ class binary_reader
 
             case 0x58: // Binary data (one-byte uint8_t for n follows)
             {
-                return get_cbor_sized_bytes<std::uint8_t>("binary", result);
+                std::uint8_t len{};
+                return get_number(len) &&
+                       get_binary(len, result);
             }
 
             case 0x59: // Binary data (two-byte uint16_t for n follow)
             {
-                return get_cbor_sized_bytes<std::uint16_t>("binary", result);
+                std::uint16_t len{};
+                return get_number(len) &&
+                       get_binary(len, result);
             }
 
             case 0x5A: // Binary data (four-byte uint32_t for n follow)
             {
-                return get_cbor_sized_bytes<std::uint32_t>("binary", result);
+                std::uint32_t len{};
+                return get_number(len) &&
+                       get_binary(len, result);
             }
 
             case 0x5B: // Binary data (eight-byte uint64_t for n follow)
             {
-                return get_cbor_sized_bytes<std::uint64_t>("binary", result);
+                std::uint64_t len{};
+                return get_number(len) &&
+                       get_binary(len, result);
             }
 
             default:
@@ -1609,12 +1559,12 @@ class binary_reader
 
                 if (at_end)
                 {
-                    bool value_complete = false;
-                    if (JSON_HEDLEY_UNLIKELY(!leave_container_and_check(value_complete)))
+                    if (JSON_HEDLEY_UNLIKELY(!leave_container()))
                     {
                         return false;
                     }
-                    if (value_complete)
+                    // the value begun here is complete once its container is
+                    if (container_stack.empty())
                     {
                         return true;
                     }
@@ -1623,7 +1573,8 @@ class binary_reader
 
                 if (top.is_object)
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!read_object_key<&binary_reader::get_cbor_object_key>(key)))
+                    key.clear();
+                    if (JSON_HEDLEY_UNLIKELY(!get_cbor_object_key(key) || !sax->key(key)))
                     {
                         return false;
                     }
@@ -2094,17 +2045,20 @@ class binary_reader
 
             case 0xD9: // str 8
             {
-                return get_string_with_length<std::uint8_t>(result, context);
+                std::uint8_t len{};
+                return get_number(len) && get_string(len, result) && check_string_utf8(result, context);
             }
 
             case 0xDA: // str 16
             {
-                return get_string_with_length<std::uint16_t>(result, context);
+                std::uint16_t len{};
+                return get_number(len) && get_string(len, result) && check_string_utf8(result, context);
             }
 
             case 0xDB: // str 32
             {
-                return get_string_with_length<std::uint32_t>(result, context);
+                std::uint32_t len{};
+                return get_number(len) && get_string(len, result) && check_string_utf8(result, context);
             }
 
             default:
@@ -2201,7 +2155,7 @@ class binary_reader
                 break;
         }
 
-        return unsupported_key_type(found);
+        return last_byte_error(exception_id::invalid_string_or_size, "only string keys are supported, but found ", "object key", found);
     }
 
     /*!
@@ -2346,12 +2300,12 @@ class binary_reader
 
                 if (container_stack.back().remaining == 0)
                 {
-                    bool value_complete = false;
-                    if (JSON_HEDLEY_UNLIKELY(!leave_container_and_check(value_complete)))
+                    if (JSON_HEDLEY_UNLIKELY(!leave_container()))
                     {
                         return false;
                     }
-                    if (value_complete)
+                    // the value begun here is complete once its container is
+                    if (container_stack.empty())
                     {
                         return true;
                     }
@@ -2364,7 +2318,8 @@ class binary_reader
                 if (is_object)
                 {
                     get();
-                    if (JSON_HEDLEY_UNLIKELY(!read_object_key<&binary_reader::get_msgpack_object_key>(key)))
+                    key.clear();
+                    if (JSON_HEDLEY_UNLIKELY(!get_msgpack_object_key(key) || !sax->key(key)))
                     {
                         return false;
                     }
@@ -2548,7 +2503,8 @@ class binary_reader
         {
             case 'U':
             {
-                return get_string_with_length<std::uint8_t>(result, context);
+                std::uint8_t len{};
+                return get_number(len) && get_string(len, result) && check_string_utf8(result, context);
             }
 
             case 'i':
@@ -2581,7 +2537,8 @@ class binary_reader
                 {
                     break;
                 }
-                return get_string_with_length<std::uint16_t>(result, context);
+                std::uint16_t len{};
+                return get_number(len) && get_string(len, result) && check_string_utf8(result, context);
             }
 
             case 'm':
@@ -2590,7 +2547,8 @@ class binary_reader
                 {
                     break;
                 }
-                return get_string_with_length<std::uint32_t>(result, context);
+                std::uint32_t len{};
+                return get_number(len) && get_string(len, result) && check_string_utf8(result, context);
             }
 
             case 'M':
@@ -2599,7 +2557,8 @@ class binary_reader
                 {
                     break;
                 }
-                return get_string_with_length<std::uint64_t>(result, context);
+                std::uint64_t len{};
+                return get_number(len) && get_string(len, result) && check_string_utf8(result, context);
             }
 
             default:
@@ -3415,12 +3374,12 @@ class binary_reader
 
                 if (at_end)
                 {
-                    bool value_complete = false;
-                    if (JSON_HEDLEY_UNLIKELY(!leave_container_and_check(value_complete)))
+                    if (JSON_HEDLEY_UNLIKELY(!leave_container()))
                     {
                         return false;
                     }
-                    if (value_complete)
+                    // the value begun here is complete once its container is
+                    if (container_stack.empty())
                     {
                         return true;
                     }
@@ -3429,7 +3388,8 @@ class binary_reader
 
                 if (top.is_object)
                 {
-                    if (JSON_HEDLEY_UNLIKELY(!read_object_key<&binary_reader::get_bon8_key>(key)))
+                    key.clear();
+                    if (JSON_HEDLEY_UNLIKELY(!get_bon8_key(key) || !sax->key(key)))
                     {
                         return false;
                     }
@@ -4169,22 +4129,6 @@ class binary_reader
         return true;
     }
 
-    /*!
-    @brief read a length of type @a NumberType, then a string of that many bytes
-
-    @tparam NumberType  the type of the length field
-    @param[out] result  string the bytes are appended to
-    @param[in] context  further context information (for diagnostics)
-
-    @return whether reading and validating the string succeeded
-    */
-    template<typename NumberType>
-    bool get_string_with_length(string_t& result, const char* context)
-    {
-        NumberType len{};
-        return get_number(len) && get_string(len, result) && check_string_utf8(result, context);
-    }
-
     /*!
     @brief create a byte array by reading bytes from the input
 
@@ -4394,7 +4338,37 @@ class binary_reader
                                   const std::string& context) const
     {
         std::string error_msg = "syntax error while parsing ";
-        error_msg += input_format_name(input_format);
+
+        switch (input_format)
+        {
+            case input_format_t::cbor:
+                error_msg += "CBOR";
+                break;
+
+            case input_format_t::msgpack:
+                error_msg += "MessagePack";
+                break;
+
+            case input_format_t::ubjson:
+                error_msg += "UBJSON";
+                break;
+
+            case input_format_t::bson:
+                error_msg += "BSON";
+                break;
+
+            case input_format_t::bjdata:
+                error_msg += "BJData";
+                break;
+
+            case input_format_t::bon8:
+                error_msg += "BON8";
+                break;
+
+            case input_format_t::json: // LCOV_EXCL_LINE
+            default:            // LCOV_EXCL_LINE
+                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
+        }
 
         return concat(error_msg, ' ', context, ": ", detail);
     }

include/nlohmann/detail/input/input_adapters.hpp

@@ -67,36 +67,6 @@ namespace detail
 /// the supported input formats
 enum class input_format_t { json, cbor, msgpack, ubjson, bson, bjdata, bon8 };
 
-/// @return the name of a binary input format, as used in exception messages
-inline const char* input_format_name(const input_format_t format) noexcept
-{
-    switch (format)
-    {
-        case input_format_t::cbor:
-            return "CBOR";
-        case input_format_t::msgpack:
-            return "MessagePack";
-        case input_format_t::ubjson:
-            return "UBJSON";
-        case input_format_t::bson:
-            return "BSON";
-        case input_format_t::bjdata:
-            return "BJData";
-        case input_format_t::bon8:
-            return "BON8";
-        case input_format_t::json: // LCOV_EXCL_LINE
-        default:            // LCOV_EXCL_LINE
-            JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
-            return ""; // LCOV_EXCL_LINE
-    }
-}
-
-/// @return the message of the parse_error thrown or reported for an empty input
-inline const char* empty_input_message() noexcept
-{
-    return "attempting to parse an empty input; check that your input string or stream contains the expected JSON";
-}
-
 ////////////////////
 // input adapters //
 ////////////////////
@@ -1298,7 +1268,7 @@ inline file_input_adapter input_adapter(std::FILE* file)
 {
     if (file == nullptr)
     {
-        JSON_THROW(parse_error::create(exception_id::syntax_error, 0, empty_input_message(), nullptr));
+        JSON_THROW(parse_error::create(exception_id::syntax_error, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
     }
     return file_input_adapter(file);
 }
@@ -1307,7 +1277,7 @@ inline input_stream_adapter input_adapter(std::istream& stream)
 {
     if (stream.rdbuf() == nullptr)
     {
-        JSON_THROW(parse_error::create(exception_id::syntax_error, 0, empty_input_message(), nullptr));
+        JSON_THROW(parse_error::create(exception_id::syntax_error, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
     }
     return input_stream_adapter(stream);
 }
@@ -1332,7 +1302,7 @@ contiguous_bytes_input_adapter input_adapter(CharT b)
 {
     if (b == nullptr)
     {
-        JSON_THROW(parse_error::create(exception_id::syntax_error, 0, empty_input_message(), nullptr));
+        JSON_THROW(parse_error::create(exception_id::syntax_error, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
     }
     auto length = std::strlen(reinterpret_cast<const char*>(b));
     const auto* ptr = reinterpret_cast<const char*>(b);

include/nlohmann/detail/input/lexer.hpp

@@ -14,6 +14,7 @@
 #include <cstdio> // snprintf
 #include <cstring> // memcmp
 #include <initializer_list> // initializer_list
+#include <limits> // numeric_limits
 #include <string> // char_traits, string
 #include <utility> // move
 #include <vector> // vector
@@ -656,74 +657,194 @@ class lexer : public lexer_base<BasicJsonType>
 
                 // invalid control characters
                 case 0x00:
+                {
+                    error_message = "invalid string: control character U+0000 (NUL) must be escaped to \\u0000";
+                    return token_type::parse_error;
+                }
+
                 case 0x01:
+                {
+                    error_message = "invalid string: control character U+0001 (SOH) must be escaped to \\u0001";
+                    return token_type::parse_error;
+                }
+
                 case 0x02:
+                {
+                    error_message = "invalid string: control character U+0002 (STX) must be escaped to \\u0002";
+                    return token_type::parse_error;
+                }
+
                 case 0x03:
+                {
+                    error_message = "invalid string: control character U+0003 (ETX) must be escaped to \\u0003";
+                    return token_type::parse_error;
+                }
+
                 case 0x04:
+                {
+                    error_message = "invalid string: control character U+0004 (EOT) must be escaped to \\u0004";
+                    return token_type::parse_error;
+                }
+
                 case 0x05:
+                {
+                    error_message = "invalid string: control character U+0005 (ENQ) must be escaped to \\u0005";
+                    return token_type::parse_error;
+                }
+
                 case 0x06:
+                {
+                    error_message = "invalid string: control character U+0006 (ACK) must be escaped to \\u0006";
+                    return token_type::parse_error;
+                }
+
                 case 0x07:
+                {
+                    error_message = "invalid string: control character U+0007 (BEL) must be escaped to \\u0007";
+                    return token_type::parse_error;
+                }
+
                 case 0x08:
+                {
+                    error_message = "invalid string: control character U+0008 (BS) must be escaped to \\u0008 or \\b";
+                    return token_type::parse_error;
+                }
+
                 case 0x09:
+                {
+                    error_message = "invalid string: control character U+0009 (HT) must be escaped to \\u0009 or \\t";
+                    return token_type::parse_error;
+                }
+
                 case 0x0A:
+                {
+                    error_message = "invalid string: control character U+000A (LF) must be escaped to \\u000A or \\n";
+                    return token_type::parse_error;
+                }
+
                 case 0x0B:
+                {
+                    error_message = "invalid string: control character U+000B (VT) must be escaped to \\u000B";
+                    return token_type::parse_error;
+                }
+
                 case 0x0C:
+                {
+                    error_message = "invalid string: control character U+000C (FF) must be escaped to \\u000C or \\f";
+                    return token_type::parse_error;
+                }
+
                 case 0x0D:
+                {
+                    error_message = "invalid string: control character U+000D (CR) must be escaped to \\u000D or \\r";
+                    return token_type::parse_error;
+                }
+
                 case 0x0E:
+                {
+                    error_message = "invalid string: control character U+000E (SO) must be escaped to \\u000E";
+                    return token_type::parse_error;
+                }
+
                 case 0x0F:
+                {
+                    error_message = "invalid string: control character U+000F (SI) must be escaped to \\u000F";
+                    return token_type::parse_error;
+                }
+
                 case 0x10:
+                {
+                    error_message = "invalid string: control character U+0010 (DLE) must be escaped to \\u0010";
+                    return token_type::parse_error;
+                }
+
                 case 0x11:
+                {
+                    error_message = "invalid string: control character U+0011 (DC1) must be escaped to \\u0011";
+                    return token_type::parse_error;
+                }
+
                 case 0x12:
+                {
+                    error_message = "invalid string: control character U+0012 (DC2) must be escaped to \\u0012";
+                    return token_type::parse_error;
+                }
+
                 case 0x13:
+                {
+                    error_message = "invalid string: control character U+0013 (DC3) must be escaped to \\u0013";
+                    return token_type::parse_error;
+                }
+
                 case 0x14:
+                {
+                    error_message = "invalid string: control character U+0014 (DC4) must be escaped to \\u0014";
+                    return token_type::parse_error;
+                }
+
                 case 0x15:
+                {
+                    error_message = "invalid string: control character U+0015 (NAK) must be escaped to \\u0015";
+                    return token_type::parse_error;
+                }
+
                 case 0x16:
+                {
+                    error_message = "invalid string: control character U+0016 (SYN) must be escaped to \\u0016";
+                    return token_type::parse_error;
+                }
+
                 case 0x17:
+                {
+                    error_message = "invalid string: control character U+0017 (ETB) must be escaped to \\u0017";
+                    return token_type::parse_error;
+                }
+
                 case 0x18:
+                {
+                    error_message = "invalid string: control character U+0018 (CAN) must be escaped to \\u0018";
+                    return token_type::parse_error;
+                }
+
                 case 0x19:
+                {
+                    error_message = "invalid string: control character U+0019 (EM) must be escaped to \\u0019";
+                    return token_type::parse_error;
+                }
+
                 case 0x1A:
+                {
+                    error_message = "invalid string: control character U+001A (SUB) must be escaped to \\u001A";
+                    return token_type::parse_error;
+                }
+
                 case 0x1B:
+                {
+                    error_message = "invalid string: control character U+001B (ESC) must be escaped to \\u001B";
+                    return token_type::parse_error;
+                }
+
                 case 0x1C:
+                {
+                    error_message = "invalid string: control character U+001C (FS) must be escaped to \\u001C";
+                    return token_type::parse_error;
+                }
+
                 case 0x1D:
+                {
+                    error_message = "invalid string: control character U+001D (GS) must be escaped to \\u001D";
+                    return token_type::parse_error;
+                }
+
                 case 0x1E:
+                {
+                    error_message = "invalid string: control character U+001E (RS) must be escaped to \\u001E";
+                    return token_type::parse_error;
+                }
+
                 case 0x1F:
                 {
-                    static const std::array<const char*, 32> control_character_messages = {{
-                            "invalid string: control character U+0000 (NUL) must be escaped to \\u0000",
-                            "invalid string: control character U+0001 (SOH) must be escaped to \\u0001",
-                            "invalid string: control character U+0002 (STX) must be escaped to \\u0002",
-                            "invalid string: control character U+0003 (ETX) must be escaped to \\u0003",
-                            "invalid string: control character U+0004 (EOT) must be escaped to \\u0004",
-                            "invalid string: control character U+0005 (ENQ) must be escaped to \\u0005",
-                            "invalid string: control character U+0006 (ACK) must be escaped to \\u0006",
-                            "invalid string: control character U+0007 (BEL) must be escaped to \\u0007",
-                            "invalid string: control character U+0008 (BS) must be escaped to \\u0008 or \\b",
-                            "invalid string: control character U+0009 (HT) must be escaped to \\u0009 or \\t",
-                            "invalid string: control character U+000A (LF) must be escaped to \\u000A or \\n",
-                            "invalid string: control character U+000B (VT) must be escaped to \\u000B",
-                            "invalid string: control character U+000C (FF) must be escaped to \\u000C or \\f",
-                            "invalid string: control character U+000D (CR) must be escaped to \\u000D or \\r",
-                            "invalid string: control character U+000E (SO) must be escaped to \\u000E",
-                            "invalid string: control character U+000F (SI) must be escaped to \\u000F",
-                            "invalid string: control character U+0010 (DLE) must be escaped to \\u0010",
-                            "invalid string: control character U+0011 (DC1) must be escaped to \\u0011",
-                            "invalid string: control character U+0012 (DC2) must be escaped to \\u0012",
-                            "invalid string: control character U+0013 (DC3) must be escaped to \\u0013",
-                            "invalid string: control character U+0014 (DC4) must be escaped to \\u0014",
-                            "invalid string: control character U+0015 (NAK) must be escaped to \\u0015",
-                            "invalid string: control character U+0016 (SYN) must be escaped to \\u0016",
-                            "invalid string: control character U+0017 (ETB) must be escaped to \\u0017",
-                            "invalid string: control character U+0018 (CAN) must be escaped to \\u0018",
-                            "invalid string: control character U+0019 (EM) must be escaped to \\u0019",
-                            "invalid string: control character U+001A (SUB) must be escaped to \\u001A",
-                            "invalid string: control character U+001B (ESC) must be escaped to \\u001B",
-                            "invalid string: control character U+001C (FS) must be escaped to \\u001C",
-                            "invalid string: control character U+001D (GS) must be escaped to \\u001D",
-                            "invalid string: control character U+001E (RS) must be escaped to \\u001E",
-                            "invalid string: control character U+001F (US) must be escaped to \\u001F"
-                        }
-                    };
-                    error_message = control_character_messages[static_cast<std::size_t>(current)];
+                    error_message = "invalid string: control character U+001F (US) must be escaped to \\u001F";
                     return token_type::parse_error;
                 }
 
@@ -1696,6 +1817,15 @@ scan_number_done:
     /// significand (see scan_number_bulk_contiguous())
     bool convert_accumulated_float(const float_significand& s, std::true_type /*native*/) noexcept
     {
+        // accept() only needs to know that the value is finite (see the parser):
+        // w < 10^19, so a value below 10^max_exponent10 cannot overflow, and a
+        // value that underflows is a finite number as well. Only a token that
+        // may overflow has to be converted to find out.
+        if (JSON_HEDLEY_UNLIKELY(discard_number_values && s.exponent + 19 <= std::numeric_limits<number_float_t>::max_exponent10))
+        {
+            value_float = 0;
+            return true;
+        }
         value_float = decimal_to_float<number_float_t>(s);
         return true;
     }

include/nlohmann/detail/input/parser.hpp

@@ -56,8 +56,8 @@ using parser_callback_t =
 template<typename SAX>
 struct sax_ignores_number_text : std::false_type {};
 
-template<typename BasicJsonType, typename InputAdapterType>
-struct sax_ignores_number_text<json_sax_dom_parser<BasicJsonType, InputAdapterType>> : std::true_type {};
+template<typename BasicJsonType, typename InputAdapterType, bool Collect>
+struct sax_ignores_number_text<json_sax_dom_parser<BasicJsonType, InputAdapterType, Collect>> : std::true_type {};
 
 template<typename BasicJsonType, typename InputAdapterType>
 struct sax_ignores_number_text<json_sax_dom_callback_parser<BasicJsonType, InputAdapterType>> : std::true_type {};
@@ -131,7 +131,7 @@ class parser
         }
         else
         {
-            json_sax_dom_parser<BasicJsonType, InputAdapterType> sdp(result, allow_exceptions, &m_lexer);
+            json_sax_dom_parser<BasicJsonType, InputAdapterType, true> sdp(result, allow_exceptions, &m_lexer);
 
             // in case of an error, return a discarded value
             if (!parse_dom(sdp, strict))
@@ -165,10 +165,23 @@ class parser
 
         if (result)
         {
-            return finish_input(*sax, strict);
+            if (strict)
+            {
+                // strict mode: next byte must be EOF
+                if (get_token() != token_type::end_of_input)
+                {
+                    return syntax_error(*sax, exception_message(token_type::end_of_input, "value"));
+                }
+            }
+            else
+            {
+                // the caller keeps using the input: position it right after
+                // the value by leaving the character that terminated it
+                m_lexer.release_lookahead();
+            }
         }
 
-        return false;
+        return result;
     }
 
   private:
@@ -189,39 +202,6 @@ class parser
         return m_lexer.get_string();
     }
 
-    /*!
-    @brief apply the end-of-input handling after a value was parsed
-
-    In strict mode, the next token must be the end of the input; otherwise
-    parse_error.101 is reported through @a sax. In non-strict mode, the
-    lookahead is released so the caller can keep reading the input right after
-    the parsed value.
-
-    @param[in,out] sax  the SAX parser to report an error to
-    @param[in] strict   whether to expect the last token to be EOF
-    @return true, or what @a sax returned for the error
-    */
-    template<typename SAX>
-    bool finish_input(SAX& sax, const bool strict)
-    {
-        if (strict)
-        {
-            // strict mode: next byte must be EOF
-            if (get_token() != token_type::end_of_input)
-            {
-                return syntax_error(sax, exception_message(token_type::end_of_input, "value"));
-            }
-        }
-        else
-        {
-            // the caller keeps using the input: position it right after
-            // the value by leaving the character that terminated it
-            m_lexer.release_lookahead();
-        }
-
-        return true;
-    }
-
     /*!
     @brief run a DOM SAX parser to completion and position the lexer
 
@@ -241,7 +221,20 @@ class parser
     {
         sax_parse_internal(&sdp);
 
-        static_cast<void>(finish_input(sdp, strict));
+        if (strict)
+        {
+            // in strict mode, input must be completely read
+            if (get_token() != token_type::end_of_input)
+            {
+                syntax_error(sdp, exception_message(token_type::end_of_input, "value"));
+            }
+        }
+        else
+        {
+            // the caller keeps using the input: position it right after
+            // the value by leaving the character that terminated it
+            m_lexer.release_lookahead();
+        }
 
         return !sdp.is_errored();
     }
@@ -250,12 +243,19 @@ class parser
     JSON_HEDLEY_NON_NULL(2)
     bool sax_parse_internal(SAX* sax)
     {
+        // value to avoid a goto (see comment where set to true)
+        bool skip_to_state_evaluation = false;
+
         // stack to remember the hierarchy of structured values we are parsing
         // true = array; false = object (bytes, not std::vector<bool>, whose
         // push_back() is a call with GCC)
         std::vector<std::uint8_t> states;
-        // value to avoid a goto (see comment where set to true)
-        bool skip_to_state_evaluation = false;
+        // a document that starts with a container pushes onto the stack at
+        // once: allocate it in one step instead of growing it from 1 byte
+        if (last_token == token_type::begin_object || last_token == token_type::begin_array)
+        {
+            states.reserve(32);
+        }
 
         while (true)
         {
@@ -411,7 +411,7 @@ class parser
                     {
                         if (JSON_HEDLEY_UNLIKELY(m_lexer.get_chars_read_total() == 1))
                         {
-                            return syntax_error(*sax, empty_input_message());
+                            return syntax_error(*sax, "attempting to parse an empty input; check that your input string or stream contains the expected JSON");
                         }
 
                         return syntax_error(*sax, exception_message(token_type::literal_or_value, "value"));

include/nlohmann/detail/input/string_scan.hpp

@@ -96,7 +96,7 @@ JSON_HEDLEY_ALWAYS_INLINE std::size_t find_string_special(const unsigned char* d
 // printable ASCII except '"' and '\\' - is emitted unchanged. Note this differs
 // from is_string_special() only in that 0x7F is also a stop (it is escaped as
 // \u007f under ensure_ascii).
-constexpr bool is_ascii_copyable(unsigned char c) noexcept
+inline bool is_ascii_copyable(unsigned char c) noexcept
 {
     return c >= 0x20u && c < 0x7Fu && c != '"' && c != '\\';
 }

include/nlohmann/detail/iterators/iter_impl.hpp

@@ -108,18 +108,33 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
     {
         JSON_ASSERT(m_object != nullptr);
 
-        if (m_object->is_object())
+        switch (m_object->m_data.m_type)
+        {
+            case value_t::object:
             {
                 m_it.object_iterator = typename object_t::iterator();
+                break;
             }
-        else if (m_object->is_array())
+
+            case value_t::array:
             {
                 m_it.array_iterator = typename array_t::iterator();
+                break;
             }
-        else
+
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
             {
-            // primitive (is_primitive(), including discarded)
                 m_it.primitive_iterator = primitive_iterator_t();
+                break;
+            }
         }
     }
 
@@ -234,28 +249,33 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
     {
         JSON_ASSERT(m_object != nullptr);
 
-        if (m_object->is_object())
+        switch (m_object->m_data.m_type)
+        {
+            case value_t::object:
             {
                 m_it.object_iterator = m_object->m_data.m_value.object->end();
-        }
-        else if (m_object->is_array())
-        {
-            m_it.array_iterator = m_object->m_data.m_value.array->end();
-        }
-        else
-        {
-            // primitive (is_primitive(), including discarded)
-            m_it.primitive_iterator.set_end();
-        }
+                break;
             }
 
-    /// @throw invalid_iterator.212 if @a other points to another container
-    template<typename IterImpl>
-    JSON_HEDLEY_ALWAYS_INLINE void check_same_container(const IterImpl& other) const
+            case value_t::array:
             {
-        if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
+                m_it.array_iterator = m_object->m_data.m_value.array->end();
+                break;
+            }
+
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
             {
-            throw_literal<invalid_iterator>(exception_id::iterators_compare_different_values, "cannot compare iterators of different containers", m_object);
+                m_it.primitive_iterator.set_end();
+                break;
+            }
         }
     }
 
@@ -404,7 +424,10 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
     bool operator==(const IterImpl& other) const
     {
         // if objects are not the same, the comparison is undefined
-        check_same_container(other);
+        if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
+        {
+            throw_literal<invalid_iterator>(exception_id::iterators_compare_different_values, "cannot compare iterators of different containers", m_object);
+        }
 
         // value-initialized forward iterators can be compared, and must compare equal to other value-initialized iterators of the same type #4493
         if (m_object == nullptr)
@@ -443,7 +466,10 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
     bool operator<(const iter_impl& other) const
     {
         // if objects are not the same, the comparison is undefined
-        check_same_container(other);
+        if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
+        {
+            throw_literal<invalid_iterator>(exception_id::iterators_compare_different_values, "cannot compare iterators of different containers", m_object);
+        }
 
         // value-initialized forward iterators can be compared, and must compare equal to other value-initialized iterators of the same type #4493
         if (m_object == nullptr)
@@ -452,19 +478,26 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
             return false;
         }
 
-        if (m_object->is_object())
+        switch (m_object->m_data.m_type)
         {
+            case value_t::object:
                 throw_literal<invalid_iterator>(exception_id::iterator_order_on_object, "cannot compare order of object iterators", m_object);
-        }
 
-        if (m_object->is_array())
-        {
+            case value_t::array:
                 return (m_it.array_iterator < other.m_it.array_iterator);
-        }
 
-        // primitive (is_primitive(), including discarded)
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
                 return (m_it.primitive_iterator < other.m_it.primitive_iterator);
         }
+    }
 
     /*!
     @brief comparison: less than or equal
@@ -501,19 +534,30 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
     {
         JSON_ASSERT(m_object != nullptr);
 
-        if (m_object->is_object())
+        switch (m_object->m_data.m_type)
         {
+            case value_t::object:
                 throw_literal<invalid_iterator>(exception_id::iterator_arithmetic_on_object, "cannot use offsets with object iterators", m_object);
-        }
 
-        if (m_object->is_array())
+            case value_t::array:
             {
                 std::advance(m_it.array_iterator, i);
+                break;
             }
-        else
+
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
             {
-            // primitive (is_primitive(), including discarded)
                 m_it.primitive_iterator += i;
+                break;
+            }
         }
 
         return *this;
@@ -569,19 +613,26 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
     {
         JSON_ASSERT(m_object != nullptr);
 
-        if (m_object->is_object())
+        switch (m_object->m_data.m_type)
         {
+            case value_t::object:
                 throw_literal<invalid_iterator>(exception_id::iterator_arithmetic_on_object, "cannot use offsets with object iterators", m_object);
-        }
 
-        if (m_object->is_array())
-        {
+            case value_t::array:
                 return m_it.array_iterator - other.m_it.array_iterator;
-        }
 
-        // primitive (is_primitive(), including discarded)
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
                 return m_it.primitive_iterator - other.m_it.primitive_iterator;
         }
+    }
 
     /*!
     @brief access to successor

include/nlohmann/detail/iterators/iteration_proxy.hpp

@@ -109,9 +109,11 @@ template<typename IteratorType> class iteration_proxy_value
     {
         JSON_ASSERT(anchor.m_object != nullptr);
 
-        if (anchor.m_object->is_array())
+        switch (anchor.m_object->type())
         {
             // use integer array index as key
+            case value_t::array:
+            {
                 if (array_index != array_index_last)
                 {
                     int_to_string( array_index_str, array_index );
@@ -120,15 +122,23 @@ template<typename IteratorType> class iteration_proxy_value
                 return array_index_str;
             }
 
-        if (anchor.m_object->is_object())
-        {
             // use key from the object
+            case value_t::object:
                 return anchor.key();
-        }
 
             // use an empty key for all primitive types
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
                 return empty_str;
         }
+    }
 
     /// return value of the iterator
     typename IteratorType::reference value() const

include/nlohmann/detail/json_pointer.hpp

@@ -38,102 +38,6 @@ NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
 {
 struct json_pointer_access;
-
-/*!
-@brief result of parse_array_index()
-
-json_pointer::array_index() maps each value to the corresponding
-parse_error/out_of_range exception; json_pointer::contains() and
-get_checked_or_null(), which must not throw for an out-of-range or
-unrepresentable index, and the json_view pointer resolution switch on it
-directly instead.
-*/
-enum class array_index_status
-{
-    ok,                ///< @a s is a valid, representable array index
-    leading_zero,      ///< @a s begins with '0' but has more than one character
-    not_a_number,      ///< @a s is neither empty nor "-" and does not begin with a digit
-    unresolved,        ///< @a s could not be converted to an integer
-    exceeds_size_type  ///< @a s converts to an integer that exceeds SizeType
-};
-
-/*!
-@brief convert a JSON Pointer reference token into an array index (RFC 6901, Sect. 4)
-
-@param[in] s    reference token to be converted into an array index; its data()
-                must be NUL-terminated
-@param[out] idx the integer representation of @a s if array_index_status::ok
-                is returned; left unchanged otherwise
-
-@return whether @a s is a valid array index, and if not, why
-
-@note this function never throws; json_pointer::array_index(), the callers that
-      must not throw, and the json_view pointer resolution build on it instead
-      of each re-implementing the RFC 6901 digit rules and the range check
-@note force-inlined: as a free function template it is no longer inlined into
-      the pointer resolution, which makes JsonPointerAt up to 17% slower (#5891)
-*/
-template<typename SizeType, typename StringType>
-JSON_HEDLEY_ALWAYS_INLINE array_index_status parse_array_index(const StringType& s, SizeType& idx) noexcept
-{
-    // error condition (cf. RFC 6901, Sect. 4)
-    if (JSON_HEDLEY_UNLIKELY(s.size() > 1 && s[0] == '0'))
-    {
-        return array_index_status::leading_zero;
-    }
-
-    // error condition (cf. RFC 6901, Sect. 4); this also covers single-
-    // character tokens, so "/x" and "/xy" fail alike; "-" and the empty
-    // token are left to the conversion below and are reported as unresolved
-    if (JSON_HEDLEY_UNLIKELY(!s.empty() && !(s.size() == 1 && s[0] == '-') && !(s[0] >= '0' && s[0] <= '9')))
-    {
-        return array_index_status::not_a_number;
-    }
-
-    // fast path: up to 18 decimal digits cannot overflow unsigned long long or
-    // SizeType (9 digits for a 32-bit SizeType), so strtoull and errno are not needed
-    constexpr std::size_t max_fast_digits = sizeof(SizeType) >= 8 ? 18 : 9;
-    if (!s.empty() && s.size() <= max_fast_digits)
-    {
-        SizeType acc = 0;
-        for (std::size_t i = 0; i < s.size(); ++i)
-        {
-            const char c = s[i];
-            if (JSON_HEDLEY_UNLIKELY(c < '0' || c > '9'))
-            {
-                break; // not a plain number: let strtoull decide
-            }
-            acc = static_cast<SizeType>((acc * 10) + static_cast<SizeType>(c - '0'));
-            if (JSON_HEDLEY_UNLIKELY(i == s.size() - 1))
-            {
-                idx = acc;
-                return array_index_status::ok;
-            }
-        }
-    }
-
-    const char* p = s.data();
-    char* p_end = nullptr; // NOLINT(misc-const-correctness)
-    errno = 0; // strtoull doesn't reset errno
-    const unsigned long long res = std::strtoull(p, &p_end, 10); // NOLINT(runtime/int)
-    if (p == p_end // invalid input or empty string
-            || errno == ERANGE // out of range
-            || JSON_HEDLEY_UNLIKELY(static_cast<std::size_t>(p_end - p) != s.size())) // incomplete read
-    {
-        return array_index_status::unresolved;
-    }
-
-    // the index does not fit into SizeType; on 64-bit platforms this is
-    // only SIZE_MAX itself (see #2203 and #5395)
-    if (res >= static_cast<unsigned long long>((std::numeric_limits<SizeType>::max)()))  // NOLINT(runtime/int)
-    {
-        return array_index_status::exceeds_size_type;
-    }
-
-    idx = static_cast<SizeType>(res);
-    return array_index_status::ok;
-}
-
 }  // namespace detail
 
 /// @brief JSON Pointer defines a string syntax for identifying a specific value within a JSON document
@@ -398,28 +302,6 @@ class json_pointer
         JSON_THROW(detail::out_of_range::create(detail::exception_id::patch_on_root, "JSON pointer has no parent", nullptr));
     }
 
-    /// whether the '~' at @a pos of @a s is not followed by '0' or '1'
-    JSON_HEDLEY_ALWAYS_INLINE static bool is_invalid_escape(const string_t& s, std::size_t pos)
-    {
-        return pos == s.size() - 1 || (s[pos + 1] != '0' && s[pos + 1] != '1');
-    }
-
-    /// @throw parse_error.107 always
-    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE static void throw_missing_slash(const string_t& pointer)
-    {
-        static_cast<void>(pointer); // unused when JSON_NOEXCEPTION is defined
-        JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_missing_slash, 1, detail::concat("JSON pointer must be empty or begin with '/' - was: '", pointer, "'"), nullptr));
-    }
-
-    /// @throw parse_error.107 if a nonempty @a pointer does not begin with '/'
-    JSON_HEDLEY_ALWAYS_INLINE static void check_begins_with_slash(const string_t& pointer)
-    {
-        if (JSON_HEDLEY_UNLIKELY(pointer[0] != '/'))
-        {
-            throw_missing_slash(pointer);
-        }
-    }
-
     /// @throw out_of_range.404 always
     template<typename BasicJsonContext>
     JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE static void throw_unresolved(const string_t& reference_token, BasicJsonContext context)
@@ -429,7 +311,21 @@ class json_pointer
         JSON_THROW(detail::out_of_range::create(detail::exception_id::pointer_unresolved, detail::concat("unresolved reference token '", reference_token, "'"), context));
     }
 
-    using array_index_status = detail::array_index_status;
+    /*!
+    @brief result of @ref parse_array_index
+
+    @ref array_index maps each value to the corresponding parse_error/out_of_range
+    exception; @ref contains and @ref get_checked_or_null, which must not throw for
+    an out-of-range or unrepresentable index, switch on it directly instead.
+    */
+    enum class array_index_status
+    {
+        ok,                ///< @a s is a valid, representable array index
+        leading_zero,      ///< @a s begins with '0' but has more than one character
+        not_a_number,      ///< @a s is neither empty nor "-" and does not begin with a digit
+        unresolved,        ///< @a s could not be converted to an integer
+        exceeds_size_type  ///< @a s converts to an integer that exceeds size_type
+    };
 
     /// whether a reference token is "-" (a plain comparison with a string literal is not always inlined)
     static bool is_dash(const string_t& s) noexcept
@@ -437,11 +333,78 @@ class json_pointer
         return s.size() == 1 && s[0] == '-';
     }
 
-    /// detail::parse_array_index() for the size_type of @a BasicJsonType
+    /*!
+    @param[in] s    reference token to be converted into an array index
+    @param[out] idx the integer representation of @a s if @ref array_index_status::ok
+                     is returned; left unchanged otherwise
+
+    @return whether @a s is a valid array index, and if not, why
+
+    @note this function never throws; @ref array_index and the callers that must not
+          throw (@ref contains, @ref get_checked_or_null) build on it instead of each
+          re-implementing the RFC 6901 digit rules and the @a size_type range check
+    */
     template<typename BasicJsonType>
     static array_index_status parse_array_index(const string_t& s, typename BasicJsonType::size_type& idx) noexcept
     {
-        return detail::parse_array_index(s, idx);
+        using size_type = typename BasicJsonType::size_type;
+
+        // error condition (cf. RFC 6901, Sect. 4)
+        if (JSON_HEDLEY_UNLIKELY(s.size() > 1 && s[0] == '0'))
+        {
+            return array_index_status::leading_zero;
+        }
+
+        // error condition (cf. RFC 6901, Sect. 4); this also covers single-
+        // character tokens, so "/x" and "/xy" fail alike; "-" and the empty
+        // token are left to the conversion below and are reported as unresolved
+        if (JSON_HEDLEY_UNLIKELY(!s.empty() && !is_dash(s) && !(s[0] >= '0' && s[0] <= '9')))
+        {
+            return array_index_status::not_a_number;
+        }
+
+        // fast path: up to 18 decimal digits cannot overflow unsigned long long or
+        // size_type (9 digits for a 32-bit size_type), so strtoull and errno are not needed
+        constexpr std::size_t max_fast_digits = sizeof(size_type) >= 8 ? 18 : 9;
+        if (!s.empty() && s.size() <= max_fast_digits)
+        {
+            size_type acc = 0;
+            for (std::size_t i = 0; i < s.size(); ++i)
+            {
+                const char c = s[i];
+                if (JSON_HEDLEY_UNLIKELY(c < '0' || c > '9'))
+                {
+                    break; // not a plain number: let strtoull decide
+                }
+                acc = static_cast<size_type>((acc * 10) + static_cast<size_type>(c - '0'));
+                if (JSON_HEDLEY_UNLIKELY(i == s.size() - 1))
+                {
+                    idx = acc;
+                    return array_index_status::ok;
+                }
+            }
+        }
+
+        const char* p = s.data();
+        char* p_end = nullptr; // NOLINT(misc-const-correctness)
+        errno = 0; // strtoull doesn't reset errno
+        const unsigned long long res = std::strtoull(p, &p_end, 10); // NOLINT(runtime/int)
+        if (p == p_end // invalid input or empty string
+                || errno == ERANGE // out of range
+                || JSON_HEDLEY_UNLIKELY(static_cast<std::size_t>(p_end - p) != s.size())) // incomplete read
+        {
+            return array_index_status::unresolved;
+        }
+
+        // the index does not fit into size_type; on 64-bit platforms this is
+        // only SIZE_MAX itself (see #2203 and #5395)
+        if (res >= static_cast<unsigned long long>((std::numeric_limits<size_type>::max)()))  // NOLINT(runtime/int)
+        {
+            return array_index_status::exceeds_size_type;
+        }
+
+        idx = static_cast<size_type>(res);
+        return array_index_status::ok;
     }
 
     /*!
@@ -491,7 +454,10 @@ class json_pointer
             return reference_tokens.empty();
         }
 
-        check_begins_with_slash(reference_string);
+        if (JSON_HEDLEY_UNLIKELY(reference_string[0] != '/'))
+        {
+            JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_missing_slash, 1, detail::concat("JSON pointer must be empty or begin with '/' - was: '", reference_string, "'"), nullptr));
+        }
 
         // the whole string is validated, whether or not it matches
         const std::size_t size = reference_string.size();
@@ -499,7 +465,7 @@ class json_pointer
                 pos != string_t::npos;
                 pos = reference_string.find_first_of('~', pos + 1))
         {
-            if (JSON_HEDLEY_UNLIKELY(is_invalid_escape(reference_string, pos)))
+            if (JSON_HEDLEY_UNLIKELY(pos == size - 1 || (reference_string[pos + 1] != '0' && reference_string[pos + 1] != '1')))
             {
                 JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_invalid_escape, 0, "escape character '~' must be followed with '0' or '1'", nullptr));
             }
@@ -777,7 +743,10 @@ class json_pointer
         }
 
         const char* const data = key.data();
-        check_begins_with_slash(key);
+        if (JSON_HEDLEY_UNLIKELY(data[0] != '/'))
+        {
+            JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_missing_slash, 1, detail::concat("JSON pointer must be empty or begin with '/' - was: '", key, "'"), nullptr));
+        }
 
         // The beginning of the key that it has in common with the previous
         // one, which was checked already, is skipped: the scan starts with
@@ -810,7 +779,7 @@ class json_pointer
             else if (data[i] == '~')
             {
                 // ~ must be followed by 0 or 1
-                if (JSON_HEDLEY_UNLIKELY(is_invalid_escape(key, i)))
+                if (JSON_HEDLEY_UNLIKELY(i + 1 == size || (data[i + 1] != '0' && data[i + 1] != '1')))
                 {
                     JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_invalid_escape, 0, "escape character '~' must be followed with '0' or '1'", nullptr));
                 }
@@ -909,7 +878,9 @@ class json_pointer
                 ++end;
             }
 
-            if (ptr->is_object())
+            switch (ptr->type())
+            {
+                case detail::value_t::object:
                 {
                     token.clear();
                     token.append(begin, static_cast<std::size_t>(end - begin));
@@ -919,8 +890,10 @@ class json_pointer
                         return nullptr;
                     }
                     ptr = &it->second;
+                    break;
                 }
-            else if (ptr->is_array())
+
+                case detail::value_t::array:
                 {
                     // an index of up to 18 digits without a leading zero fits into size_type
                     // (9 digits for a 32-bit size_type); everything else is left to json_pointer
@@ -944,10 +917,18 @@ class json_pointer
                         return nullptr;
                     }
                     ptr = &(*ptr->m_data.m_value.array)[idx];
+                    break;
                 }
-            else
-            {
-                // primitive value with a reference token left
+
+                case detail::value_t::null:
+                case detail::value_t::string:
+                case detail::value_t::boolean:
+                case detail::value_t::number_integer:
+                case detail::value_t::number_unsigned:
+                case detail::value_t::number_float:
+                case detail::value_t::binary:
+                case detail::value_t::discarded:
+                default:
                     return nullptr;
             }
             pos = static_cast<std::size_t>(end - path.data());
@@ -998,12 +979,16 @@ class json_pointer
                        : detail::value_t::object;
             }
 
-            if (ptr->is_object())
+            switch (ptr->type())
+            {
+                case detail::value_t::object:
                 {
                     // use unchecked object access
                     ptr = &object_member(*ptr, reference_token);
+                    break;
                 }
-            else if (ptr->is_array())
+
+                case detail::value_t::array:
                 {
                     if (reference_token == "-")
                     {
@@ -1015,10 +1000,18 @@ class json_pointer
                         // convert array index to number; unchecked access
                         ptr = &ptr->operator[](array_index<BasicJsonType>(reference_token));
                     }
+                    break;
                 }
-            else
-            {
-                // primitive value with a reference token left
+
+                case detail::value_t::null:
+                case detail::value_t::string:
+                case detail::value_t::boolean:
+                case detail::value_t::number_integer:
+                case detail::value_t::number_unsigned:
+                case detail::value_t::number_float:
+                case detail::value_t::binary:
+                case detail::value_t::discarded:
+                default:
                     throw_unresolved(reference_token, ptr);
             }
         }
@@ -1037,7 +1030,9 @@ class json_pointer
     {
         for (const auto& reference_token : reference_tokens)
         {
-            if (ptr->is_object())
+            switch (ptr->type())
+            {
+                case detail::value_t::object:
                 {
                     const auto it = ptr->m_data.m_value.object->find(reference_token);
                     if (JSON_HEDLEY_UNLIKELY(it == ptr->m_data.m_value.object->end()))
@@ -1046,8 +1041,10 @@ class json_pointer
                         ptr->at(reference_token);
                     }
                     ptr = &it->second;
+                    break;
                 }
-            else if (ptr->is_array())
+
+                case detail::value_t::array:
                 {
                     if (JSON_HEDLEY_UNLIKELY(is_dash(reference_token)))
                     {
@@ -1065,10 +1062,18 @@ class json_pointer
                                 "array index ", std::to_string(idx), " is out of range"), ptr));
                     }
                     ptr = &(*ptr->m_data.m_value.array)[idx];
+                    break;
                 }
-            else
-            {
-                // primitive value with a reference token left
+
+                case detail::value_t::null:
+                case detail::value_t::string:
+                case detail::value_t::boolean:
+                case detail::value_t::number_integer:
+                case detail::value_t::number_unsigned:
+                case detail::value_t::number_float:
+                case detail::value_t::binary:
+                case detail::value_t::discarded:
+                default:
                     throw_unresolved(reference_token, ptr);
             }
         }
@@ -1098,15 +1103,19 @@ class json_pointer
     {
         for (const auto& reference_token : reference_tokens)
         {
-            if (ptr->is_object())
+            switch (ptr->type())
+            {
+                case detail::value_t::object:
                 {
                     // use unchecked object access; the const operator[]
                     // asserts that the key exists
                     const auto it = ptr->m_data.m_value.object->find(reference_token);
                     JSON_ASSERT(it != ptr->m_data.m_value.object->end());
                     ptr = &it->second;
+                    break;
                 }
-            else if (ptr->is_array())
+
+                case detail::value_t::array:
                 {
                     if (JSON_HEDLEY_UNLIKELY(is_dash(reference_token)))
                     {
@@ -1119,10 +1128,18 @@ class json_pointer
                     const auto idx = array_index<BasicJsonType>(reference_token);
                     JSON_ASSERT(idx < ptr->m_data.m_value.array->size());
                     ptr = &(*ptr->m_data.m_value.array)[idx];
+                    break;
                 }
-            else
-            {
-                // primitive value with a reference token left
+
+                case detail::value_t::null:
+                case detail::value_t::string:
+                case detail::value_t::boolean:
+                case detail::value_t::number_integer:
+                case detail::value_t::number_unsigned:
+                case detail::value_t::number_float:
+                case detail::value_t::binary:
+                case detail::value_t::discarded:
+                default:
                     throw_unresolved(reference_token, ptr);
             }
         }
@@ -1147,7 +1164,9 @@ class json_pointer
     {
         for (const auto& reference_token : reference_tokens)
         {
-            if (ptr->is_object())
+            switch (ptr->type())
+            {
+                case detail::value_t::object:
                 {
                     const auto it = ptr->m_data.m_value.object->find(reference_token);
                     if (JSON_HEDLEY_UNLIKELY(it == ptr->m_data.m_value.object->end()))
@@ -1155,8 +1174,10 @@ class json_pointer
                         return nullptr;
                     }
                     ptr = &it->second;
+                    break;
                 }
-            else if (ptr->is_array())
+
+                case detail::value_t::array:
                 {
                     if (JSON_HEDLEY_UNLIKELY(is_dash(reference_token)))
                     {
@@ -1190,10 +1211,18 @@ class json_pointer
                         return nullptr;
                     }
                     ptr = &(*ptr->m_data.m_value.array)[idx];
+                    break;
                 }
-            else
-            {
-                // primitive value with a reference token left
+
+                case detail::value_t::null:
+                case detail::value_t::string:
+                case detail::value_t::boolean:
+                case detail::value_t::number_integer:
+                case detail::value_t::number_unsigned:
+                case detail::value_t::number_float:
+                case detail::value_t::binary:
+                case detail::value_t::discarded:
+                default:
                     return nullptr;
             }
         }
@@ -1210,7 +1239,9 @@ class json_pointer
     {
         for (const auto& reference_token : reference_tokens)
         {
-            if (ptr->is_object())
+            switch (ptr->type())
+            {
+                case detail::value_t::object:
                 {
                     const auto it = ptr->m_data.m_value.object->find(reference_token);
                     if (it == ptr->m_data.m_value.object->end())
@@ -1220,8 +1251,10 @@ class json_pointer
                     }
 
                     ptr = &it->second;
+                    break;
                 }
-            else if (ptr->is_array())
+
+                case detail::value_t::array:
                 {
                     if (JSON_HEDLEY_UNLIKELY(is_dash(reference_token)))
                     {
@@ -1246,14 +1279,25 @@ class json_pointer
                     }
 
                     ptr = &(*ptr->m_data.m_value.array)[idx];
+                    break;
                 }
-            else
+
+                case detail::value_t::null:
+                case detail::value_t::string:
+                case detail::value_t::boolean:
+                case detail::value_t::number_integer:
+                case detail::value_t::number_unsigned:
+                case detail::value_t::number_float:
+                case detail::value_t::binary:
+                case detail::value_t::discarded:
+                default:
                 {
                     // we do not expect primitive values if there is still a
                     // reference token to process
                     return false;
                 }
             }
+        }
 
         // no reference token left means we found a primitive value
         return true;
@@ -1279,7 +1323,10 @@ class json_pointer
         }
 
         // check if a nonempty reference string begins with slash
-        check_begins_with_slash(reference_string);
+        if (JSON_HEDLEY_UNLIKELY(reference_string[0] != '/'))
+        {
+            JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_missing_slash, 1, detail::concat("JSON pointer must be empty or begin with '/' - was: '", reference_string, "'"), nullptr));
+        }
 
         // every slash starts a reference token
         const std::size_t size = reference_string.size();
@@ -1320,7 +1367,9 @@ class json_pointer
                     JSON_ASSERT(reference_token[pos] == '~');
 
                     // ~ must be followed by 0 or 1
-                    if (JSON_HEDLEY_UNLIKELY(is_invalid_escape(reference_token, pos)))
+                    if (JSON_HEDLEY_UNLIKELY(pos == reference_token.size() - 1 ||
+                                             (reference_token[pos + 1] != '0' &&
+                                              reference_token[pos + 1] != '1')))
                     {
                         JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_invalid_escape, 0, "escape character '~' must be followed with '0' or '1'", nullptr));
                     }
@@ -1477,7 +1526,9 @@ class json_pointer
         auto hint = object.end();
         const auto enter = [&stack, &path, &object, &hint](const BasicJsonType & v)
         {
-            if (v.is_array())
+            switch (v.type())
+            {
+                case detail::value_t::array:
                 {
                     if (v.m_data.m_value.array->empty())
                     {
@@ -1488,8 +1539,10 @@ class json_pointer
                     {
                         stack.emplace_back(&v, object_const_iterator(), path.size());
                     }
+                    return;
                 }
-            else if (v.is_object())
+
+                case detail::value_t::object:
                 {
                     if (v.m_data.m_value.object->empty())
                     {
@@ -1500,11 +1553,23 @@ class json_pointer
                     {
                         stack.emplace_back(&v, v.m_data.m_value.object->begin(), path.size());
                     }
+                    return;
                 }
-            else
+
+                case detail::value_t::null:
+                case detail::value_t::string:
+                case detail::value_t::boolean:
+                case detail::value_t::number_integer:
+                case detail::value_t::number_unsigned:
+                case detail::value_t::number_float:
+                case detail::value_t::binary:
+                case detail::value_t::discarded:
+                default:
                 {
                     // add a primitive value with its reference string
                     add_flattened(object, hint, path, v, detail::priority_tag<2> {});
+                    return;
+                }
             }
         };
 

include/nlohmann/detail/output/binary_writer.hpp

@@ -21,7 +21,6 @@
 
 #include <nlohmann/detail/bit_ops.hpp>
 #include <nlohmann/detail/input/binary_reader.hpp>
-#include <nlohmann/detail/input/input_adapters.hpp>
 #include <nlohmann/detail/input/string_scan.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/output/error_handler.hpp>
@@ -312,7 +311,9 @@ class binary_writer
                 write_cbor_head(0x40, N);
 
                 // step 2: write each element
-                write_bytes(j.m_data.m_value.binary->data(), N);
+                oa.write_characters(
+                      reinterpret_cast<const CharType*>(j.m_data.m_value.binary->data()),
+                      N);
 
                 break;
             }
@@ -325,7 +326,7 @@ class binary_writer
 
             case value_t::discarded:
             default:
-                throw_on_discarded(j, input_format_t::cbor);
+                throw_on_discarded(j, "CBOR");
         }
     }
 
@@ -525,7 +526,9 @@ class binary_writer
                 }
 
                 // step 2: write the byte string
-                write_bytes(j.m_data.m_value.binary->data(), N);
+                oa.write_characters(
+                      reinterpret_cast<const CharType*>(j.m_data.m_value.binary->data()),
+                      N);
 
                 break;
             }
@@ -539,7 +542,7 @@ class binary_writer
 
             case value_t::discarded:
             default:
-                throw_on_discarded(j, input_format_t::msgpack);
+                throw_on_discarded(j, "MessagePack");
         }
     }
 
@@ -623,7 +626,7 @@ class binary_writer
             case value_t::array:
             {
                 bool prefix_required = true;
-                const bool write_closer = write_ubjson_start_container<true>(j, use_count, use_type, add_prefix, use_bjdata, prefix_required);
+                const bool write_closer = write_ubjson_start_array(j, use_count, use_type, add_prefix, use_bjdata, prefix_required);
 
                 {
                     const auto& array = *j.m_data.m_value.array;
@@ -673,7 +676,9 @@ class binary_writer
 
                 if (use_type)
                 {
-                    write_bytes(j.m_data.m_value.binary->data(), j.m_data.m_value.binary->size());
+                    oa.write_characters(
+                          reinterpret_cast<const CharType*>(j.m_data.m_value.binary->data()),
+                          j.m_data.m_value.binary->size());
                 }
                 else
                 {
@@ -699,7 +704,7 @@ class binary_writer
                 }
 
                 bool prefix_required = true;
-                const bool write_closer = write_ubjson_start_container<false>(j, use_count, use_type, add_prefix, use_bjdata, prefix_required);
+                const bool write_closer = write_ubjson_start_object(j, use_count, use_type, add_prefix, use_bjdata, prefix_required);
 
                 write_ubjson_members(j, use_count, use_type, prefix_required, use_bjdata, bjdata_version, depth);
 
@@ -713,7 +718,7 @@ class binary_writer
 
             case value_t::discarded:
             default:
-                throw_on_discarded(j, use_bjdata ? input_format_t::bjdata : input_format_t::ubjson);
+                throw_on_discarded(j, use_bjdata ? "BJData" : "UBJSON");
         }
     }
 
@@ -739,11 +744,11 @@ class binary_writer
     @brief throws because @a j is discarded and cannot be serialized
     @throw type_error.321 always
     */
-    JSON_HEDLEY_NO_RETURN static void throw_on_discarded(const BasicJsonType& j, const input_format_t format)
+    JSON_HEDLEY_NO_RETURN static void throw_on_discarded(const BasicJsonType& j, const char* format_name)
     {
         static_cast<void>(j); // unused when JSON_NOEXCEPTION is defined
-        static_cast<void>(format);
-        JSON_THROW(type_error::create(exception_id::discarded_value_used, concat("cannot serialize discarded value to ", input_format_name(format)), &j));
+        static_cast<void>(format_name);
+        JSON_THROW(type_error::create(exception_id::discarded_value_used, concat("cannot serialize discarded value to ", format_name), &j));
     }
 
     /// how the range of integer type @a NumberType relates to that of @a TargetType
@@ -863,11 +868,11 @@ class binary_writer
     }
 
     /*!
-    @brief throws because the integer @a j is too large for @a format
+    @brief throws because the integer @a j is too large for @a format_name
     @throw out_of_range.407 always
     */
     JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE
-    static void throw_integer_out_of_range(const BasicJsonType& j, const input_format_t format, const char* range)
+    static void throw_integer_out_of_range(const BasicJsonType& j, const char* format_name, const char* range)
     {
         // neither std::to_string(), which has no overload for integer types
         // wider than 64 bits, nor dump(), which would also instantiate the
@@ -878,9 +883,9 @@ class binary_writer
                                    ? integer_to_string(j.m_data.m_value.number_unsigned, std::integral_constant<bool, unsigned_limits::is_signed>())
                                    : integer_to_string(j.m_data.m_value.number_integer, std::integral_constant<bool, integer_limits::is_signed>());
         static_cast<void>(number); // unused when JSON_NOEXCEPTION is defined
-        static_cast<void>(format);
+        static_cast<void>(format_name);
         static_cast<void>(range);
-        JSON_THROW(out_of_range::create(exception_id::integer_too_large, concat("integer number ", number, " cannot be represented by ", input_format_name(format), " as it does not fit ", range), &j));
+        JSON_THROW(out_of_range::create(exception_id::integer_too_large, concat("integer number ", number, " cannot be represented by ", format_name, " as it does not fit ", range), &j));
     }
 
     // The exceptions below are thrown from functions of their own, out of line:
@@ -923,56 +928,53 @@ class binary_writer
         JSON_THROW(other_error::create(exception_id::size_marker_required, "use_type requires use_size = true", &j));
     }
 
-    /// @brief write @a size bytes starting at @a data to the output adapter
-    JSON_HEDLEY_ALWAYS_INLINE
-    void write_bytes(const void* data, const std::size_t size)
-    {
-        oa.write_characters(static_cast<const CharType*>(data), size);
-    }
-
-    /// @brief write the MessagePack prefix of an array or object with @a N
-    ///        elements: the fix marker @a fix_marker | n, or @a marker_16 or
-    ///        @a marker_32 followed by the length
-    JSON_HEDLEY_ALWAYS_INLINE
-    void write_msgpack_container_prefix(const std::size_t N, const BasicJsonType& j,
-                                        const std::uint8_t fix_marker, const std::uint8_t marker_16, const std::uint8_t marker_32)
+    void write_msgpack_array_prefix(const std::size_t N, const BasicJsonType& j)
     {
         const auto n = to_msgpack_length(N, j);
         if (n <= 15)
         {
-            // fixarray, fixmap
-            oa.write_character(to_char_type(static_cast<std::uint8_t>(fix_marker | n)));
+            // fixarray
+            oa.write_character(to_char_type(static_cast<std::uint8_t>(0x90 | n)));
         }
         else if (n <= (std::numeric_limits<std::uint16_t>::max)())
         {
-            // array 16, map 16
-            oa.write_character(to_char_type(marker_16));
+            // array 16
+            oa.write_character(to_char_type(0xDC));
             write_number(static_cast<std::uint16_t>(n));
         }
         else
         {
-            // array 32, map 32
-            oa.write_character(to_char_type(marker_32));
+            // array 32
+            oa.write_character(to_char_type(0xDD));
             write_number(static_cast<std::uint32_t>(n));
         }
     }
 
-    JSON_HEDLEY_ALWAYS_INLINE
-    void write_msgpack_array_prefix(const std::size_t N, const BasicJsonType& j)
-    {
-        write_msgpack_container_prefix(N, j, 0x90, 0xDC, 0xDD);
-    }
-
-    JSON_HEDLEY_ALWAYS_INLINE
     void write_msgpack_object_prefix(const std::size_t N, const BasicJsonType& j)
     {
-        write_msgpack_container_prefix(N, j, 0x80, 0xDE, 0xDF);
+        const auto n = to_msgpack_length(N, j);
+        if (n <= 15)
+        {
+            // fixmap
+            oa.write_character(to_char_type(static_cast<std::uint8_t>(0x80 | (n & 0xF))));
+        }
+        else if (n <= (std::numeric_limits<std::uint16_t>::max)())
+        {
+            // map 16
+            oa.write_character(to_char_type(0xDE));
+            write_number(static_cast<std::uint16_t>(n));
+        }
+        else
+        {
+            // map 32
+            oa.write_character(to_char_type(0xDF));
+            write_number(static_cast<std::uint32_t>(n));
+        }
     }
 
-    /// @brief a CBOR, MessagePack, BON8, or (as the base of @ref ubjson_frame)
-    ///        UBJSON array or object whose elements @ref write_container_iterative,
-    ///        @ref write_bon8_iterative, or @ref write_ubjson_iterative is still
-    ///        writing
+    /// @brief a CBOR, MessagePack, or BON8 array or object whose elements
+    ///        @ref write_cbor_iterative, @ref write_msgpack_iterative, or
+    ///        @ref write_bon8_iterative is still writing
     struct binary_container_frame
     {
         explicit binary_container_frame(const BasicJsonType* value_) noexcept
@@ -1008,82 +1010,19 @@ class binary_writer
         typename BasicJsonType::array_t::const_iterator array_it{};
     };
 
-    /// @brief the CBOR specifics of @ref write_container_iterative
-    struct cbor_walk
-    {
-        static void array_head(binary_writer& w, const BasicJsonType& j)
-        {
-            w.write_cbor_head(0x80, j.m_data.m_value.array->size());
-        }
-
-        static void object_head(binary_writer& w, const BasicJsonType& j)
-        {
-            w.write_cbor_head(0xA0, j.m_data.m_value.object->size());
-        }
-
-        static void scalar(binary_writer& w, const BasicJsonType& j)
-        {
-            w.write_cbor(j);
-        }
-
-        static void string(binary_writer& w, const string_t& key, const BasicJsonType& context)
-        {
-            w.write_cbor_string(key, context);
-        }
-
-        template<typename KeyType>
-        static void key(binary_writer& w, const KeyType& k, const BasicJsonType& object)
-        {
-            w.write_cbor_key(k, object);
-        }
-    };
-
-    /// @brief the MessagePack specifics of @ref write_container_iterative
-    struct msgpack_walk
-    {
-        static void array_head(binary_writer& w, const BasicJsonType& j)
-        {
-            w.write_msgpack_array_prefix(j.m_data.m_value.array->size(), j);
-        }
-
-        static void object_head(binary_writer& w, const BasicJsonType& j)
-        {
-            w.write_msgpack_object_prefix(j.m_data.m_value.object->size(), j);
-        }
-
-        static void scalar(binary_writer& w, const BasicJsonType& j)
-        {
-            w.write_msgpack(j);
-        }
-
-        static void string(binary_writer& w, const string_t& key, const BasicJsonType& context)
-        {
-            w.write_msgpack_string(key, context);
-        }
-
-        template<typename KeyType>
-        static void key(binary_writer& w, const KeyType& k, const BasicJsonType& object)
-        {
-            w.write_msgpack_key(k, object);
-        }
-    };
-
     /*!
-    @brief write @a j with @a Walk::scalar, or write its header and push a
-           frame for @ref write_container_iterative to continue with its
-           elements
+    @brief write @a j with @ref write_cbor, or write its header and push a
+           frame for @ref write_cbor_iterative to continue with its elements
 
     A scalar, and an empty array or object, are written out in full: there is
-    nothing below them for @ref write_container_iterative to come back to, so
+    nothing below them for @ref write_cbor_iterative to come back to, so
     nothing is pushed for them.
     */
-    template<typename Walk>
-    JSON_HEDLEY_ALWAYS_INLINE
-    void write_container_value_or_push(const BasicJsonType& j, std::vector<binary_container_frame>& stack)
+    void write_cbor_value_or_push(const BasicJsonType& j, std::vector<binary_container_frame>& stack)
     {
         if (j.is_array())
         {
-            Walk::array_head(*this, j);
+            write_cbor_head(0x80, j.m_data.m_value.array->size());
             if (!j.m_data.m_value.array->empty())
             {
                 stack.emplace_back(&j);
@@ -1093,7 +1032,7 @@ class binary_writer
 
         if (j.is_object())
         {
-            Walk::object_head(*this, j);
+            write_cbor_head(0xA0, j.m_data.m_value.object->size());
             if (!j.m_data.m_value.object->empty())
             {
                 stack.emplace_back(&j);
@@ -1101,26 +1040,22 @@ class binary_writer
             return;
         }
 
-        Walk::scalar(*this, j);
+        write_cbor(j);
     }
 
     /*!
     @brief write out @a root and everything below it without the call stack
 
-    Emits the same bytes as the recursive writer, keeping the containers it has
+    Emits the same bytes as @ref write_cbor, keeping the containers it has
     entered on an explicit stack instead of descending into them. Only reached
     for values nested deeper than @ref recursion_depth_limit, which is why it
-    is not written for speed. Shared by CBOR and MessagePack, which differ only
-    in the @a Walk policy (@ref cbor_walk, @ref msgpack_walk); BON8 has its own
-    walker, as it tracks an open string run and closes a container with a
-    marker.
+    is not written for speed.
     */
-    template<typename Walk>
-    void write_container_iterative(const BasicJsonType& root)
+    void write_cbor_iterative(const BasicJsonType& root)
     {
-        // only a container with elements is ever pushed; see write_container_value_or_push
+        // only a container with elements is ever pushed; see write_cbor_value_or_push
         std::vector<binary_container_frame> stack;
-        write_container_value_or_push<Walk>(root, stack);
+        write_cbor_value_or_push(root, stack);
 
         while (!stack.empty())
         {
@@ -1138,7 +1073,7 @@ class binary_writer
                 // read the child before pushing: entering it can move every frame
                 const BasicJsonType* child = &(*current.array_it);
                 ++stack.back().array_it;
-                write_container_value_or_push<Walk>(*child, stack);
+                write_cbor_value_or_push(*child, stack);
             }
             else
             {
@@ -1150,53 +1085,110 @@ class binary_writer
                 }
 
                 // the key is written directly (not via a temporary basic_json),
-                // with the object as diagnostics context, as in the recursive writer
-                Walk::key(*this, current.object_it->first, *current.value);
+                // with the object as diagnostics context, as in write_cbor
+                write_cbor_key(current.object_it->first, *current.value);
                 const BasicJsonType* child = &(current.object_it->second);
                 ++stack.back().object_it;
-                write_container_value_or_push<Walk>(*child, stack);
+                write_cbor_value_or_push(*child, stack);
             }
         }
     }
 
-    void write_cbor_iterative(const BasicJsonType& root)
-    {
-        write_container_iterative<cbor_walk>(root);
-    }
-
-    void write_msgpack_iterative(const BasicJsonType& root)
-    {
-        write_container_iterative<msgpack_walk>(root);
-    }
-
     /*!
-    @brief write the start of an array (@a IsArray) or object: its opening
-           marker, the optimized type, and the count
+    @brief write @a j with @ref write_msgpack, or write its header and push a
+           frame for @ref write_msgpack_iterative to continue with its elements
 
-    @return true when a closing ']' or '}' still has to be written after the
-            elements
+    @sa @ref write_cbor_value_or_push
     */
-    template<bool IsArray>
-    bool write_ubjson_start_container(const BasicJsonType& j, const bool use_count, const bool use_type,
+    void write_msgpack_value_or_push(const BasicJsonType& j, std::vector<binary_container_frame>& stack)
+    {
+        if (j.is_array())
+        {
+            write_msgpack_array_prefix(j.m_data.m_value.array->size(), j);
+            if (!j.m_data.m_value.array->empty())
+            {
+                stack.emplace_back(&j);
+            }
+            return;
+        }
+
+        if (j.is_object())
+        {
+            write_msgpack_object_prefix(j.m_data.m_value.object->size(), j);
+            if (!j.m_data.m_value.object->empty())
+            {
+                stack.emplace_back(&j);
+            }
+            return;
+        }
+
+        write_msgpack(j);
+    }
+
+    /*!
+    @brief write out @a root and everything below it without the call stack
+
+    @sa @ref write_cbor_iterative
+    */
+    void write_msgpack_iterative(const BasicJsonType& root)
+    {
+        std::vector<binary_container_frame> stack;
+        write_msgpack_value_or_push(root, stack);
+
+        while (!stack.empty())
+        {
+            const binary_container_frame current = stack.back();
+
+            if (current.value->is_array())
+            {
+                const auto& array = *current.value->m_data.m_value.array;
+                if (current.array_it == array.cend())
+                {
+                    stack.pop_back();
+                    continue;
+                }
+
+                const BasicJsonType* child = &(*current.array_it);
+                ++stack.back().array_it;
+                write_msgpack_value_or_push(*child, stack);
+            }
+            else
+            {
+                const auto& object = *current.value->m_data.m_value.object;
+                if (current.object_it == object.cend())
+                {
+                    stack.pop_back();
+                    continue;
+                }
+
+                // as in write_cbor_iterative, the key is written directly with
+                // the object as diagnostics context
+                write_msgpack_key(current.object_it->first, *current.value);
+                const BasicJsonType* child = &(current.object_it->second);
+                ++stack.back().object_it;
+                write_msgpack_value_or_push(*child, stack);
+            }
+        }
+    }
+
+    /// @return true when a closing ']' still has to be written after the elements
+    bool write_ubjson_start_array(const BasicJsonType& j, const bool use_count, const bool use_type,
                                   const bool add_prefix, const bool use_bjdata, bool& prefix_required)
     {
         prefix_required = true;
         if (add_prefix)
         {
-            oa.write_character(to_char_type(IsArray ? '[' : '{'));
+            oa.write_character(to_char_type('['));
         }
 
-        const std::size_t size = IsArray ? j.m_data.m_value.array->size() : j.m_data.m_value.object->size();
-
-        if (use_type && size != 0)
+        if (use_type && !j.m_data.m_value.array->empty())
         {
             if (!use_count)
             {
                 throw_size_marker_required(j);
             }
             const CharType first_prefix = ubjson_prefix(j.front(), use_bjdata);
-            // the first element of an array has been compared with itself
-            const bool same_prefix = std::all_of(IsArray ? j.begin() + 1 : j.begin(), j.end(),
+            const bool same_prefix = std::all_of(j.begin() + 1, j.end(),
                                                  [this, first_prefix, use_bjdata](const BasicJsonType & v)
             {
                 return ubjson_prefix(v, use_bjdata) == first_prefix;
@@ -1208,9 +1200,8 @@ class binary_writer
             // those, at one byte per element, so the result can be read back.
             // Objects are not affected: every element is preceded by its key.
             const bool valueless_type = (first_prefix == 'Z' || first_prefix == 'T' || first_prefix == 'F');
-            const bool excessive_valueless = IsArray
-                                             && valueless_type
-                                             && size > detail::max_valueless_container_size;
+            const bool excessive_valueless = valueless_type
+                                             && j.m_data.m_value.array->size() > detail::max_valueless_container_size;
 
             if (same_prefix && !excessive_valueless
                     && !(use_bjdata && is_bjdata_excluded_type_marker(first_prefix)))
@@ -1223,7 +1214,46 @@ class binary_writer
 
         if (use_count)
         {
-            write_ubjson_count(size, use_bjdata);
+            write_ubjson_count(j.m_data.m_value.array->size(), use_bjdata);
+        }
+
+        return !use_count;
+    }
+
+    /// @return true when a closing '}' still has to be written after the elements
+    bool write_ubjson_start_object(const BasicJsonType& j, const bool use_count, const bool use_type,
+                                   const bool add_prefix, const bool use_bjdata, bool& prefix_required)
+    {
+        prefix_required = true;
+        if (add_prefix)
+        {
+            oa.write_character(to_char_type('{'));
+        }
+
+        if (use_type && !j.m_data.m_value.object->empty())
+        {
+            if (!use_count)
+            {
+                throw_size_marker_required(j);
+            }
+            const CharType first_prefix = ubjson_prefix(j.front(), use_bjdata);
+            const bool same_prefix = std::all_of(j.begin(), j.end(),
+                                                 [this, first_prefix, use_bjdata](const BasicJsonType & v)
+            {
+                return ubjson_prefix(v, use_bjdata) == first_prefix;
+            });
+
+            if (same_prefix && !(use_bjdata && is_bjdata_excluded_type_marker(first_prefix)))
+            {
+                prefix_required = false;
+                oa.write_character(to_char_type('$'));
+                oa.write_character(first_prefix);
+            }
+        }
+
+        if (use_count)
+        {
+            write_ubjson_count(j.m_data.m_value.object->size(), use_bjdata);
         }
 
         return !use_count;
@@ -1251,12 +1281,21 @@ class binary_writer
 
     /// @brief an object or array @ref write_ubjson_iterative is still writing
     ///        the elements of
-    struct ubjson_frame : binary_container_frame
+    struct ubjson_frame
     {
         ubjson_frame(const BasicJsonType* value_, const bool prefix_required_) noexcept
-            : binary_container_frame(value_)
+            : value(value_)
             , prefix_required(prefix_required_)
-        {}
+        {
+            if (value->is_object())
+            {
+                object_it = value->m_data.m_value.object->cbegin();
+            }
+            else
+            {
+                array_it = value->m_data.m_value.array->cbegin();
+            }
+        }
 
         // declared for GCC's -Weffc++, which asks for them in a class with
         // pointer members and a non-trivial destructor; the exception
@@ -1268,9 +1307,13 @@ class binary_writer
         ubjson_frame& operator=(ubjson_frame&&) = default;
         ~ubjson_frame() = default;
 
+        /// the array or object being written
+        const BasicJsonType* value;
         /// whether value's elements each carry their own type marker; an
         /// optimized ($type) container writes it once for all of them instead
         bool prefix_required;
+        typename BasicJsonType::object_t::const_iterator object_it{};
+        typename BasicJsonType::array_t::const_iterator array_it{};
     };
 
     /*!
@@ -1281,7 +1324,7 @@ class binary_writer
                elements of an optimized container, and everything below the
                top level, never repeat it)
 
-    @sa @ref write_container_value_or_push
+    @sa @ref write_cbor_value_or_push
     */
     void write_ubjson_value_or_push(const BasicJsonType& j, const bool add_prefix, const bool use_count,
                                     const bool use_type, const bool use_bjdata, const bjdata_version_t bjdata_version,
@@ -1304,11 +1347,11 @@ class binary_writer
         bool prefix_required = true;
         if (is_array)
         {
-            write_ubjson_start_container<true>(j, use_count, use_type, add_prefix, use_bjdata, prefix_required);
+            write_ubjson_start_array(j, use_count, use_type, add_prefix, use_bjdata, prefix_required);
         }
         else
         {
-            write_ubjson_start_container<false>(j, use_count, use_type, add_prefix, use_bjdata, prefix_required);
+            write_ubjson_start_object(j, use_count, use_type, add_prefix, use_bjdata, prefix_required);
         }
 
         const bool empty = is_array ? j.m_data.m_value.array->empty() : j.m_data.m_value.object->empty();
@@ -1318,7 +1361,7 @@ class binary_writer
             return;
         }
 
-        // write_ubjson_start_container returns !use_count, i.e. whether a
+        // write_ubjson_start_array/_object return !use_count, i.e. whether a
         // closer still has to be written; use_count is constant for the whole
         // document, so that is recomputed here instead of being carried along
         if (!use_count)
@@ -1507,15 +1550,14 @@ class binary_writer
     {
         oa.write_character(to_char_type(element_type));
 
-        if (JSON_HEDLEY_LIKELY(error_handler == error_handler_t::keep || error_handler == error_handler_t::strict))
+        if (error_handler == error_handler_t::keep || error_handler == error_handler_t::strict || is_valid_utf8(name))
         {
-            write_bytes(name.data(), name.size());
+            oa.write_characters(reinterpret_cast<const CharType*>(name.data()), name.size());
         }
         else
         {
-            string_t storage;
-            const string_t& written = sanitize_utf8_for_bson_write(name, storage);
-            write_bytes(written.data(), written.size());
+            const string_t sanitized = sanitize_utf8(name, error_handler);
+            oa.write_characters(reinterpret_cast<const CharType*>(sanitized.data()), sanitized.size());
         }
 
         // the terminating null byte is written explicitly rather than taken
@@ -1591,11 +1633,16 @@ class binary_writer
     {
         write_bson_entry_header(name, 0x02);
 
-        string_t storage;
-        const string_t& written = sanitize_utf8_for_bson_write(value, storage);
+        const bool sanitize = error_handler != error_handler_t::keep
+                              && error_handler != error_handler_t::strict
+                              && !is_valid_utf8(value);
+        const string_t sanitized = sanitize ? sanitize_utf8(value, error_handler) : string_t{};
+        const string_t& written = sanitize ? sanitized : value;
 
         write_number<std::int32_t>(to_bson_length(written.size() + 1ul), true);
-        write_bytes(written.data(), written.size());
+        oa.write_characters(
+              reinterpret_cast<const CharType*>(written.data()),
+              written.size());
         // the terminating null byte is written explicitly rather than taken
         // from the buffer, so that string_t::data() need not be null-terminated
         oa.write_character(to_char_type(0x00));
@@ -1701,7 +1748,7 @@ class binary_writer
 
         write_number(value.has_subtype() ? static_cast<std::uint8_t>(value.subtype()) : static_cast<std::uint8_t>(0x00));
 
-        write_bytes(value.data(), value.size());
+        oa.write_characters(reinterpret_cast<const CharType*>(value.data()), value.size());
     }
 
     /*!
@@ -1731,14 +1778,14 @@ class binary_writer
             case value_t::number_integer:
                 if (JSON_HEDLEY_UNLIKELY(!integer_fits<std::int64_t>(j.m_data.m_value.number_integer)))
                 {
-                    throw_integer_out_of_range(j, input_format_t::bson, "int64");
+                    throw_integer_out_of_range(j, "BSON", "int64");
                 }
                 return calc_bson_integer_size(static_cast<std::int64_t>(j.m_data.m_value.number_integer));
 
             case value_t::number_unsigned:
                 if (JSON_HEDLEY_UNLIKELY(!integer_fits_max<std::uint64_t>(j.m_data.m_value.number_unsigned)))
                 {
-                    throw_integer_out_of_range(j, input_format_t::bson, "uint64");
+                    throw_integer_out_of_range(j, "BSON", "uint64");
                 }
                 return calc_bson_unsigned_size(conditional_static_cast<std::uint64_t>(j.m_data.m_value.number_unsigned));
 
@@ -1749,7 +1796,7 @@ class binary_writer
                 return 0ul;
 
             case value_t::discarded:
-                throw_on_discarded(j, input_format_t::bson);
+                throw_on_discarded(j, "BSON");
 
             // LCOV_EXCL_START
             case value_t::object:
@@ -1913,7 +1960,7 @@ class binary_writer
             // the terminating null byte is written explicitly rather than
             // taken from the buffer, so that string_t::data() need not be
             // null-terminated
-            write_bytes(value.data(), value.size());
+            oa.write_characters(reinterpret_cast<const CharType*>(value.data()), value.size());
             oa.write_character(to_char_type(0x00));
             return true;
         }
@@ -1930,7 +1977,7 @@ class binary_writer
             p += sizeof(std::int32_t);
             *p++ = value.has_subtype() ? to_char_type(static_cast<std::uint8_t>(value.subtype())) : to_char_type(0x00);
             oa.commit(static_cast<std::size_t>(p - out));
-            write_bytes(value.data(), value.size());
+            oa.write_characters(reinterpret_cast<const CharType*>(value.data()), value.size());
             return true;
         }
 
@@ -1978,7 +2025,7 @@ class binary_writer
                 return write_bson_null(name);
 
             case value_t::discarded:
-                throw_on_discarded(j, input_format_t::bson);
+                throw_on_discarded(j, "BSON");
 
             // LCOV_EXCL_START
             case value_t::object:
@@ -2759,7 +2806,7 @@ class binary_writer
         {
             if (JSON_HEDLEY_UNLIKELY(!integer_fits_max<std::uint64_t>(j.m_data.m_value.number_unsigned)))
             {
-                throw_integer_out_of_range(j, input_format_t::cbor, "uint64");
+                throw_integer_out_of_range(j, "CBOR", "uint64");
             }
             write_cbor_head(0x00, conditional_static_cast<std::uint64_t>(j.m_data.m_value.number_unsigned));
             return;
@@ -2769,7 +2816,7 @@ class binary_writer
         {
             if (JSON_HEDLEY_UNLIKELY(!integer_fits_max<std::uint64_t>(j.m_data.m_value.number_integer)))
             {
-                throw_integer_out_of_range(j, input_format_t::cbor, "[-2^64, 2^64-1]");
+                throw_integer_out_of_range(j, "CBOR", "[-2^64, 2^64-1]");
             }
             // CBOR does not differentiate between positive signed
             // integers and unsigned integers
@@ -2780,7 +2827,7 @@ class binary_writer
             // a negative integer n is encoded as -1 - n
             if (JSON_HEDLEY_UNLIKELY(!integer_fits_max<std::uint64_t>(-1 - j.m_data.m_value.number_integer)))
             {
-                throw_integer_out_of_range(j, input_format_t::cbor, "[-2^64, 2^64-1]");
+                throw_integer_out_of_range(j, "CBOR", "[-2^64, 2^64-1]");
             }
             write_cbor_head(0x20, static_cast<std::uint64_t>(-1 - j.m_data.m_value.number_integer));
         }
@@ -2856,7 +2903,7 @@ class binary_writer
         {
             if (JSON_HEDLEY_UNLIKELY(!integer_fits_max<std::uint64_t>(j.m_data.m_value.number_unsigned)))
             {
-                throw_integer_out_of_range(j, input_format_t::msgpack, "uint64");
+                throw_integer_out_of_range(j, "MessagePack", "uint64");
             }
             write_msgpack_unsigned(static_cast<std::uint64_t>(j.m_data.m_value.number_unsigned));
             return;
@@ -2866,7 +2913,7 @@ class binary_writer
         {
             if (JSON_HEDLEY_UNLIKELY(!integer_fits_max<std::uint64_t>(j.m_data.m_value.number_integer)))
             {
-                throw_integer_out_of_range(j, input_format_t::msgpack, "[-2^63, 2^64-1]");
+                throw_integer_out_of_range(j, "MessagePack", "[-2^63, 2^64-1]");
             }
             // MessagePack does not differentiate between positive
             // signed integers and unsigned integers.
@@ -2876,7 +2923,7 @@ class binary_writer
         {
             if (JSON_HEDLEY_UNLIKELY(!integer_fits_min<std::int64_t>(j.m_data.m_value.number_integer)))
             {
-                throw_integer_out_of_range(j, input_format_t::msgpack, "[-2^63, 2^64-1]");
+                throw_integer_out_of_range(j, "MessagePack", "[-2^63, 2^64-1]");
             }
             if (j.m_data.m_value.number_integer >= -32)
             {
@@ -3010,37 +3057,40 @@ class binary_writer
     }
 
     /*!
-    @brief write an object key as a CBOR or MessagePack string (@a Walk)
+    @brief write an object key as a CBOR text string
 
     A key convertible to string_t is written directly. Other key types (only
     an explicit conversion, or only a to_json overload) go through a temporary
     basic_json, as in version 3.12.0; the temporary is then the diagnostics
     context for strict UTF-8 checks.
     */
-    template<typename Walk, typename Key = typename BasicJsonType::object_t::key_type,
+    template<typename Key = typename BasicJsonType::object_t::key_type,
              enable_if_t<std::is_convertible<Key, string_t>::value, int> = 0>
-    void write_object_key(const typename BasicJsonType::object_t::key_type& key, const BasicJsonType& context)
-    {
-        Walk::string(*this, key, context);
-    }
-
-    template<typename Walk, typename Key = typename BasicJsonType::object_t::key_type,
-             enable_if_t<negation<std::is_convertible<Key, string_t>>::value, int> = 0>
-    void write_object_key(const typename BasicJsonType::object_t::key_type& key, const BasicJsonType& /*context*/)
-    {
-        Walk::scalar(*this, BasicJsonType(key));
-    }
-
-    /// @brief write an object key as a CBOR text string
     void write_cbor_key(const typename BasicJsonType::object_t::key_type& key, const BasicJsonType& context)
     {
-        write_object_key<cbor_walk>(key, context);
+        write_cbor_string(key, context);
     }
 
-    /// @brief write an object key as a MessagePack str
+    template < typename Key = typename BasicJsonType::object_t::key_type,
+               enable_if_t < !std::is_convertible<Key, string_t>::value, int > = 0 >
+    void write_cbor_key(const typename BasicJsonType::object_t::key_type& key, const BasicJsonType& /*context*/)
+    {
+        write_cbor(BasicJsonType(key));
+    }
+
+    /// @brief write an object key as a MessagePack str, as in @ref write_cbor_key
+    template<typename Key = typename BasicJsonType::object_t::key_type,
+             enable_if_t<std::is_convertible<Key, string_t>::value, int> = 0>
     void write_msgpack_key(const typename BasicJsonType::object_t::key_type& key, const BasicJsonType& context)
     {
-        write_object_key<msgpack_walk>(key, context);
+        write_msgpack_string(key, context);
+    }
+
+    template < typename Key = typename BasicJsonType::object_t::key_type,
+               enable_if_t < !std::is_convertible<Key, string_t>::value, int > = 0 >
+    void write_msgpack_key(const typename BasicJsonType::object_t::key_type& key, const BasicJsonType& /*context*/)
+    {
+        write_msgpack(BasicJsonType(key));
     }
 
     /// the longest string that is written, with its head of one or two
@@ -3115,7 +3165,9 @@ class binary_writer
         write_cbor_head(0x60, sanitized.size());
 
         // step 2: write the string
-        write_bytes(sanitized.data(), sanitized.size());
+        oa.write_characters(
+              reinterpret_cast<const CharType*>(sanitized.data()),
+              sanitized.size());
     }
 
     /////////////
@@ -3196,7 +3248,9 @@ class binary_writer
         }
 
         // step 2: write the string
-        write_bytes(sanitized.data(), sanitized.size());
+        oa.write_characters(
+              reinterpret_cast<const CharType*>(sanitized.data()),
+              sanitized.size());
     }
 
     ////////////
@@ -3479,7 +3533,9 @@ class binary_writer
             oa.write_character(to_char_type('S'));
         }
         write_number_with_ubjson_prefix(sanitized.size(), true, use_bjdata);
-        write_bytes(sanitized.data(), sanitized.size());
+        oa.write_characters(
+              reinterpret_cast<const CharType*>(sanitized.data()),
+              sanitized.size());
     }
 
     /*!
@@ -4279,7 +4335,7 @@ class binary_writer
             {
                 if (JSON_HEDLEY_UNLIKELY(!integer_fits_max<std::int64_t>(j.m_data.m_value.number_unsigned)))
                 {
-                    throw_integer_out_of_range(j, input_format_t::bon8, "int64");
+                    throw_integer_out_of_range(j, "BON8", "int64");
                 }
                 write_bon8_integer(static_cast<std::int64_t>(j.m_data.m_value.number_unsigned));
                 string_open = false;
@@ -4290,7 +4346,7 @@ class binary_writer
             {
                 if (JSON_HEDLEY_UNLIKELY(!integer_fits<std::int64_t>(j.m_data.m_value.number_integer)))
                 {
-                    throw_integer_out_of_range(j, input_format_t::bon8, "int64");
+                    throw_integer_out_of_range(j, "BON8", "int64");
                 }
                 write_bon8_integer(static_cast<std::int64_t>(j.m_data.m_value.number_integer));
                 string_open = false;
@@ -4358,7 +4414,7 @@ class binary_writer
 
             case value_t::discarded:
             default:
-                throw_on_discarded(j, input_format_t::bon8);
+                throw_on_discarded(j, "BON8");
         }
     }
 
@@ -4369,7 +4425,7 @@ class binary_writer
     A scalar, and an empty array or object, are written out in full and not
     pushed.
 
-    @sa @ref write_container_value_or_push
+    @sa @ref write_cbor_value_or_push
     */
     void write_bon8_value_or_push(const BasicJsonType& j, bool& string_open, std::vector<binary_container_frame>& stack)
     {
@@ -4755,7 +4811,7 @@ class binary_writer
         }
         else
         {
-            write_bytes(s.data(), s.size());
+            oa.write_characters(reinterpret_cast<const CharType*>(s.data()), s.size());
             string_open = true;
         }
     }
@@ -4846,31 +4902,6 @@ class binary_writer
         }
     }
 
-    /*!
-    @brief the write-pass counterpart of @ref sanitize_utf8_for_write for BSON
-
-    The size pass (@ref calc_bson_entry_header_size, @ref
-    calc_bson_string_size) has already validated @a s, and thrown for @ref
-    error_handler_t::strict if it was ill-formed. Here, @ref
-    error_handler_t::strict therefore behaves like @ref error_handler_t::keep,
-    and @ref error_handler_t::replace / @ref error_handler_t::ignore produce
-    exactly the bytes the size pass measured. Hence no context is needed.
-
-    @param[in] s        the string (value or object key) to write
-    @param[out] storage  backing storage for a sanitized copy
-
-    @return a reference to @a s, or to @a storage once it holds a sanitized copy
-    */
-    const string_t& sanitize_utf8_for_bson_write(const string_t& s, string_t& storage) const
-    {
-        if (error_handler == error_handler_t::keep || error_handler == error_handler_t::strict || is_valid_utf8(s))
-        {
-            return s; // NOLINT(bugprone-return-const-ref-from-parameter): callers pass lvalues that outlive the call
-        }
-        storage = sanitize_utf8(s, error_handler);
-        return storage;
-    }
-
     /// deleted: anything but a string_t would bind a temporary that dies before the returned reference is used
     template < typename T, enable_if_t < !std::is_same<T, string_t>::value, int > = 0 >
     const string_t& sanitize_utf8_for_write(const T& /*s*/, const BasicJsonType& /*context*/, string_t& /*storage*/) const = delete; // NOLINT(hicpp-use-equals-delete,modernize-use-equals-delete): a private helper's guard, not part of the interface

include/nlohmann/detail/output/serializer.hpp

@@ -966,28 +966,6 @@ class serializer
         }
     }
 
-    /// write out the bytes pending in @ref string_buffer and reset @a bytes
-    JSON_HEDLEY_ALWAYS_INLINE void emit_pending(std::size_t& bytes)
-    {
-        if (bytes != 0)
-        {
-            put_buffer(string_buffer, bytes);
-            bytes = 0;
-        }
-    }
-
-    /// write buffer and reset index if fewer than 13 bytes are left, as this
-    /// is the maximal number of bytes to be written ("\uxxxx\uxxxx\0") for one
-    /// code point
-    JSON_HEDLEY_ALWAYS_INLINE void reserve_string_buffer(std::size_t& bytes)
-    {
-        if (string_buffer.size() - bytes < 13)
-        {
-            put_buffer(string_buffer, bytes);
-            bytes = 0;
-        }
-    }
-
     /*!
     @brief worker for @ref dump_escaped
 
@@ -1046,7 +1024,11 @@ class serializer
                 {
                     // emit any bytes still pending in string_buffer first to
                     // preserve output order, then write the run directly
-                    emit_pending(bytes);
+                    if (bytes != 0)
+                    {
+                        put_buffer(string_buffer, bytes);
+                        bytes = 0;
+                    }
                     put_run(s, i, run);
                     bytes_after_last_accept = 0;
                     undumped_chars = 0;
@@ -1067,10 +1049,11 @@ class serializer
                 {
                     // emit any bytes still pending in string_buffer first to
                     // preserve output order
-                    emit_pending(bytes);
-                    // deliberately not put_buffer(): a fixed 8-byte memcpy
-                    // has no asserts and no write-through branch, which
-                    // matters on the hot path
+                    if (bytes != 0)
+                    {
+                        put_buffer(string_buffer, bytes);
+                        bytes = 0;
+                    }
                     const auto& escape = ascii_escapes()[data[i]];
                     if (JSON_HEDLEY_UNLIKELY(write_buffer.size() - write_buffer_pos < escape.size()))
                     {
@@ -1145,7 +1128,14 @@ class serializer
                         string_buffer[bytes++] = s[i];
                     }
 
-                    reserve_string_buffer(bytes);
+                    // write buffer and reset index; there must be 13 bytes
+                    // left, as this is the maximal number of bytes to be
+                    // written ("\uxxxx\uxxxx\0") for one code point
+                    if (string_buffer.size() - bytes < 13)
+                    {
+                        put_buffer(string_buffer, bytes);
+                        bytes = 0;
+                    }
 
                     // remember the byte position of this accept
                     bytes_after_last_accept = bytes;
@@ -1197,7 +1187,14 @@ class serializer
                                     string_buffer[bytes++] = '\xBD';
                                 }
 
-                                reserve_string_buffer(bytes);
+                                // write buffer and reset index; there must be 13 bytes
+                                // left, as this is the maximal number of bytes to be
+                                // written ("\uxxxx\uxxxx\0") for one code point
+                                if (string_buffer.size() - bytes < 13)
+                                {
+                                    put_buffer(string_buffer, bytes);
+                                    bytes = 0;
+                                }
 
                                 bytes_after_last_accept = bytes;
                             }
@@ -1230,7 +1227,14 @@ class serializer
                                 string_buffer[bytes++] = s[i];
                             }
 
-                            reserve_string_buffer(bytes);
+                            // write buffer and reset index; there must be 13 bytes
+                            // left, as this is the maximal number of bytes to be
+                            // written ("\uxxxx\uxxxx\0") for one code point
+                            if (string_buffer.size() - bytes < 13)
+                            {
+                                put_buffer(string_buffer, bytes);
+                                bytes = 0;
+                            }
 
                             bytes_after_last_accept = bytes;
                             undumped_chars = 0;
@@ -1596,15 +1600,28 @@ class serializer
     */
     static const std::array<std::uint8_t, 256>& ascii_copyable() noexcept
     {
-        // constant-initialized from the predicate: no runtime loop, no guard
-        static constexpr std::array<std::uint8_t, 256> copyable = make_ascii_copyable(make_index_sequence<256> {});
-        return copyable;
-    }
-
-    template<std::size_t... Is>
-    static constexpr std::array<std::uint8_t, 256> make_ascii_copyable(index_sequence<Is...> /*unused*/) noexcept
+        static const std::array<std::uint8_t, 256> copyable =
         {
-        return {{ static_cast<std::uint8_t>(is_ascii_copyable(static_cast<unsigned char>(Is)) ? 1 : 0)... }};
+            {
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x00
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x10
+                1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x20
+                1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x30
+                1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x40
+                1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, // 0x50
+                1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x60
+                1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, // 0x70
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x80
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0x90
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xA0
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xB0
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xC0
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xD0
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0xE0
+                0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 // 0xF0
+            }
+        };
+        return copyable;
     }
 
     /*!
@@ -1735,6 +1752,7 @@ class serializer
     */
     JSON_HEDLEY_NEVER_INLINE std::size_t write_u_escapes(const unsigned char* data, std::size_t n)
     {
+        constexpr const char* nibble_to_hex = "0123456789abcdef";
         std::size_t i = 0;
         while (i < n && data[i] >= 0x80)
         {
@@ -1771,21 +1789,26 @@ class serializer
             char* d = write_buffer.data() + write_buffer_pos;
             if (codepoint > 0xFFFFu)
             {
-                d = put_u_escape(d, static_cast<std::uint16_t>(0xD7C0u + (codepoint >> 10u)));
+                d = put_u_escape(d, static_cast<std::uint16_t>(0xD7C0u + (codepoint >> 10u)), nibble_to_hex);
                 codepoint = 0xDC00u + (codepoint & 0x3FFu);
             }
-            d = put_u_escape(d, static_cast<std::uint16_t>(codepoint));
+            d = put_u_escape(d, static_cast<std::uint16_t>(codepoint), nibble_to_hex);
             write_buffer_pos = static_cast<std::size_t>(d - write_buffer.data());
             i += length;
         }
         return i;
     }
 
-    static char* put_u_escape(char* d, const std::uint16_t codeunit) noexcept
+    static char* put_u_escape(char* d, const std::uint16_t codeunit, const char* nibble_to_hex) noexcept
     {
+        const auto unit = static_cast<std::uint32_t>(codeunit);
         d[0] = '\\';
         d[1] = 'u';
-        return hex4_lower(codeunit, d + 2);
+        d[2] = nibble_to_hex[(unit >> 12u) & 0x0Fu];
+        d[3] = nibble_to_hex[(unit >> 8u) & 0x0Fu];
+        d[4] = nibble_to_hex[(unit >> 4u) & 0x0Fu];
+        d[5] = nibble_to_hex[unit & 0x0Fu];
+        return d + 6;
     }
 
     /*!
@@ -1794,7 +1817,7 @@ class serializer
      * Branch-free replacement for `snprintf(buf, 7, "\\u%04x", codeunit)` in the
      * string escaping hot path. It writes exactly six characters ('\\', 'u' and
      * four hex digits) at position @a pos of @a string_buffer via a nibble
-     * lookup table (@ref hex4_lower), avoiding the format-string parsing and locale machinery of
+     * lookup table, avoiding the format-string parsing and locale machinery of
      * `snprintf`. Advances @a pos by the number of bytes written (6).
      *
      * @param[in] pos       position in @a string_buffer to write at; there must
@@ -1804,9 +1827,13 @@ class serializer
     void write_u_escape(std::size_t& pos, std::uint16_t codeunit) noexcept
     {
         JSON_ASSERT(string_buffer.size() - pos >= 6);
+        constexpr const char* nibble_to_hex = "0123456789abcdef";
         string_buffer[pos + 0] = '\\';
         string_buffer[pos + 1] = 'u';
-        hex4_lower(codeunit, &string_buffer[pos + 2]);
+        string_buffer[pos + 2] = nibble_to_hex[(codeunit >> 12u) & 0x0Fu];
+        string_buffer[pos + 3] = nibble_to_hex[(codeunit >> 8u) & 0x0Fu];
+        string_buffer[pos + 4] = nibble_to_hex[(codeunit >> 4u) & 0x0Fu];
+        string_buffer[pos + 5] = nibble_to_hex[codeunit & 0x0Fu];
         pos += 6;
     }
 

include/nlohmann/detail/string_utils.hpp

@@ -48,24 +48,6 @@ inline std::string hex_byte(const std::uint8_t byte)
     return result;
 }
 
-/*!
-@brief write a UTF-16 code unit as four lowercase hexadecimal digits
-
-The lowercase counterpart of hex_byte(), used for the `\\uXXXX` escapes of the
-serializers, whose output is lowercase. Writes exactly four characters to
-@a out and returns the pointer past them.
-*/
-JSON_HEDLEY_ALWAYS_INLINE char* hex4_lower(const std::uint16_t codeunit, char* out) noexcept
-{
-    constexpr const char* nibble_to_hex = "0123456789abcdef";
-    const unsigned int unit = codeunit;
-    out[0] = nibble_to_hex[(unit >> 12u) & 0x0Fu];
-    out[1] = nibble_to_hex[(unit >> 8u) & 0x0Fu];
-    out[2] = nibble_to_hex[(unit >> 4u) & 0x0Fu];
-    out[3] = nibble_to_hex[unit & 0x0Fu];
-    return out + 4;
-}
-
 ///////////////////
 // UTF-8 encoding //
 ///////////////////
@@ -121,66 +103,6 @@ void encode_utf8(std::uint32_t cp, const Out& out)
     }
 }
 
-/*!
-@brief the shape of a well-formed UTF-8 sequence, by its lead byte
-
-@a length is 1 for ASCII, 2 to 4 for a valid lead byte, and 0 for a byte that
-cannot start a well-formed sequence (a continuation byte, 0xC0, 0xC1, or 0xF5
-to 0xFF). For a multibyte sequence, the second byte must lie in
-[@a second_lo, @a second_hi], and every later byte in [0x80, 0xBF]
-(RFC 3629, section 4; Unicode Table 3-7). The narrower second-byte ranges
-exclude overlong forms (0xE0, 0xF0), surrogates (0xED), and code points
-beyond U+10FFFF (0xF4).
-*/
-struct utf8_sequence_shape
-{
-    std::uint8_t length;
-    std::uint8_t second_lo;
-    std::uint8_t second_hi;
-};
-
-/// @return the shape of a UTF-8 sequence starting with @a lead, see utf8_sequence_shape
-inline utf8_sequence_shape utf8_shape(const std::uint8_t lead) noexcept
-{
-    if (lead < 0x80u)
-    {
-        return {1, 0, 0};
-    }
-    if (lead < 0xC2u)
-    {
-        return {0, 0, 0};
-    }
-    if (lead <= 0xDFu)
-    {
-        return {2, 0x80u, 0xBFu};
-    }
-    if (lead == 0xE0u)
-    {
-        return {3, 0xA0u, 0xBFu};
-    }
-    if (lead == 0xEDu)
-    {
-        return {3, 0x80u, 0x9Fu};
-    }
-    if (lead <= 0xEFu)
-    {
-        return {3, 0x80u, 0xBFu};
-    }
-    if (lead == 0xF0u)
-    {
-        return {4, 0x90u, 0xBFu};
-    }
-    if (lead <= 0xF3u)
-    {
-        return {4, 0x80u, 0xBFu};
-    }
-    if (lead == 0xF4u)
-    {
-        return {4, 0x80u, 0x8Fu};
-    }
-    return {0, 0, 0};
-}
-
 ///////////////////
 // UTF-8 decoding //
 ///////////////////
@@ -196,7 +118,7 @@ This is a single-byte step of a "shift-based" UTF-8 decoder originally
 written by Björn Hoehrmann. See
 http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ for details.
 
-The library checks UTF-8 well-formedness (RFC 3629, section 4) in five
+The library checks UTF-8 well-formedness (RFC 3629, section 4) in three
 places, which differ in speed, diagnostics, and how they read the input:
 
 - decode() below: the serializer, to escape and, in strict mode, reject
@@ -210,15 +132,10 @@ places, which differ in speed, diagnostics, and how they read the input:
   bulk string scan, the bulk path of the BON8 reader, and the BON8 writer.
   They must accept exactly what the lexer's switch accepts.
 - the byte path of binary_reader::get_bon8_string(): BON8 input without bulk
-  access, and the bytes the bulk path leaves to it. It keeps its own ranges:
-  taking them from utf8_shape() made BON8 decoding 2-3% slower (#5891).
-- check_utf8() in detail/view/edit.hpp: strings stored in an editable
-  json_document, with the index of the offending byte. It also uses
-  utf8_shape().
+  access, and the bytes the bulk path leaves to it.
 
-All five must accept the same set of sequences, which the test "UTF-8
-validators accept the same sequences" in unit-class_lexer.cpp checks
-exhaustively against decode() and utf8_shape().
+All four must accept the same set of sequences, so a change to one needs a
+matching change to the others.
 
 @param[in,out] state  the current decoder state
 @param[in,out] codep  codepoint (valid only if resulting state is UTF8_ACCEPT)

include/nlohmann/detail/value_t.hpp

@@ -177,36 +177,6 @@ inline bool owns_memory(const value_t t) noexcept
     }
 }
 
-/*!
-@brief whether a value of the given type is neither an object nor an array
-
-Unlike basic_json::is_primitive(), this includes value_t::discarded: it names
-the types that iterators walk with a primitive_iterator_t (a single value, or no
-value for null and discarded) and that JSON Pointer resolution and the
-serializer treat as leaves. Every enumerator is listed so that -Wswitch-enum
-flags this function when a new type is added.
-*/
-inline bool is_primitive(const value_t t) noexcept
-{
-    switch (t)
-    {
-        case value_t::object:
-        case value_t::array:
-            return false;
-
-        case value_t::null:
-        case value_t::string:
-        case value_t::boolean:
-        case value_t::number_integer:
-        case value_t::number_unsigned:
-        case value_t::number_float:
-        case value_t::binary:
-        case value_t::discarded:
-        default:
-            return true;
-    }
-}
-
 
 /*!
 @brief compare an integer with a floating point number without precision loss

include/nlohmann/detail/view/builder.hpp

@@ -275,11 +275,34 @@ class builder
                 0, 0, '\b', 0, 0, 0, '\f', 0, 0, 0, 0, 0, 0, 0, '\n', 0, 0, 0, '\r', 0, '\t', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
             }
         };
+        // The write position is kept in locals: the stores of characters into
+        // the arena may alias the members of the builder, which would then be
+        // reloaded after every one. It is stored back where the arena grows,
+        // and by `write_back` on every return.
+        const unsigned char* const end = m_end;
         const std::size_t start = arena_used();
-        arena_run(s, static_cast<std::size_t>(p - s));
+        char* w = m_arena_write;
+        const char* w_end = m_arena_end;
+        const arena_write_back write_back(*this, w);
+        {
+            const auto n = static_cast<std::size_t>(p - s);
+            if (n <= 16 && end - s >= 16)
+            {
+                arena_ensure(w, w_end, 16);
+                std::memcpy(w, s, 16);
+            }
+            else if (n != 0)
+            {
+                // (an empty run leaves an empty arena unallocated, and memcpy()
+                // must not be passed its null pointer even for zero bytes)
+                arena_ensure(w, w_end, n);
+                std::memcpy(w, s, n);
+            }
+            w += n;
+        }
         for (;;)
         {
-            if (p == m_end)
+            if (p == end)
             {
                 return failed(error_code::string_missing_quote, p);
             }
@@ -287,7 +310,9 @@ class builder
             if (c == '"')
             {
                 ++p;
-                return decoded{p, start, arena_used() - start};
+                // (from w: `write_back` stores it only after the return value
+                // is made; the arena is allocated, since an escape was written)
+                return decoded{p, start, static_cast<std::size_t>(w - m_doc.arena.data()) - start};
             }
             if (c != '\\')
             {
@@ -297,7 +322,7 @@ class builder
                 return failed(c < 0x20 ? error_code::string_control_character : error_code::string_utf8, p);
             }
             ++p;
-            if (p == m_end)
+            if (p == end)
             {
                 return failed(error_code::string_missing_quote, p);
             }
@@ -315,7 +340,7 @@ class builder
                     {
                         return failed(error_code::string_surrogate_low, p);
                     }
-                    if (m_end - p < 2 || p[0] != '\\' || p[1] != 'u')
+                    if (end - p < 2 || p[0] != '\\' || p[1] != 'u')
                     {
                         return failed(error_code::string_surrogate_high, p);
                     }
@@ -331,26 +356,106 @@ class builder
                     }
                     cp = 0x10000 + ((cp - 0xD800) << 10) + (lo - 0xDC00);
                 }
-                arena_ensure(4);
-                m_arena_write = put_utf8(m_arena_write, cp);
+                arena_ensure(w, w_end, 4);
+                w = put_utf8(w, cp);
             }
             else if (NLOHMANN_VIEW_LIKELY(d < 128 && simple_escape[d] != 0))
             {
-                arena_ensure(1);
-                *m_arena_write++ = simple_escape[d];
+                arena_ensure(w, w_end, 1);
+                *w++ = simple_escape[d];
             }
             else
             {
                 --p;
                 return failed(error_code::string_escape, p);
             }
-            if (p != m_end && *p == '\\')
+#if NLOHMANN_VIEW_NEON
+            if (p != end && *p == '\\')
             {
                 continue; // consecutive escapes ("\u00e4\u00f6"): no run in between
             }
+            // The first 16 bytes of the run are checked one by one, in predicted branches, and copied
+            // as one block: where the runs between escapes are short, the vector step below would put
+            // its longer dependency chain (load, compare, mask, count, add) on p for each of them,
+            // and be slower than these steps (the scanner of the keys works the same way)
+            {
+                if (end - p >= 16)
+                {
+                    const std::uint8_t* const plain = string_plain();
+                    std::size_t steps = 16;
+#define NLOHMANN_VIEW_STEP(i) if (NLOHMANN_VIEW_LIKELY(plain[p[i]] != 0)) {} else { steps = (i); goto run_found; }
+                    NLOHMANN_VIEW_REPEAT16(NLOHMANN_VIEW_STEP)
+#undef NLOHMANN_VIEW_STEP
+run_found:
+                    arena_ensure(w, w_end, 16);
+                    std::memcpy(w, p, 16); // (only the first `steps` bytes are kept)
+                    w += steps;
+                    p += steps;
+                    if (steps < 16)
+                    {
+                        if (*p >= 0x80)
+                        {
+                            // non-ASCII: the UTF-8 check, and the rest of the run
                             const unsigned char* const r = p;
-            p = scan_string_run(p, m_end);
-            arena_run(r, static_cast<std::size_t>(p - r));
+                            p = scan_string_run(p, end);
+                            const auto n = static_cast<std::size_t>(p - r);
+                            arena_ensure(w, w_end, n);
+                            std::memcpy(w, r, n);
+                            w += n;
+                        }
+                        continue;
+                    }
+                }
+            }
+#else
+            if (p != end && (*p == '\\' || *p == '"'))
+            {
+                continue; // consecutive escapes ("\u00e4\u00f6"), or the end of the string: no run in between
+            }
+#endif
+#if NLOHMANN_VIEW_VECTOR
+            // the plain bytes up to the next quote, backslash, or control
+            // character are copied as they are scanned, 16 bytes at a time
+            for (;;)
+            {
+                if (NLOHMANN_VIEW_UNLIKELY(end - p < 16))
+                {
+                    const unsigned char* const r = p;
+                    p = scan_string_run(p, end);
+                    const auto n = static_cast<std::size_t>(p - r);
+                    arena_ensure(w, w_end, n);
+                    std::memcpy(w, r, n);
+                    w += n;
+                    break;
+                }
+                arena_ensure(w, w_end, 16);
+                const unsigned k = copy_plain_run16(p, w);
+                w += k;
+                p += k;
+                if (k == 16)
+                {
+                    continue;
+                }
+                if (NLOHMANN_VIEW_UNLIKELY(*p >= 0x80))
+                {
+                    // non-ASCII: the UTF-8 check, and the rest of the run
+                    const unsigned char* const r = p;
+                    p = scan_string_run(p, end);
+                    const auto n = static_cast<std::size_t>(p - r);
+                    arena_ensure(w, w_end, n);
+                    std::memcpy(w, r, n);
+                    w += n;
+                }
+                break;
+            }
+#else
+            const unsigned char* const r = p;
+            p = scan_string_run(p, end);
+            const auto n = static_cast<std::size_t>(p - r);
+            arena_ensure(w, w_end, n);
+            std::memcpy(w, r, n);
+            w += n;
+#endif
         }
     }
 
@@ -392,19 +497,49 @@ class builder
     char* m_arena_write = nullptr;
     char* m_arena_end = nullptr;
 
+    /// room for n more bytes at w, the write position kept in a local, with
+    /// w_end the end of the arena. (A lambda instead is not always inlined,
+    /// and then w would be kept in memory, as m_arena_write is.)
+    NLOHMANN_VIEW_ALWAYS_INLINE void arena_ensure(char*& w, const char*& w_end, std::size_t n)
+    {
+        if (NLOHMANN_VIEW_UNLIKELY(static_cast<std::size_t>(w_end - w) < n))
+        {
+            m_arena_write = w;
+            arena_grow(n);
+            w = m_arena_write;
+            w_end = m_arena_end;
+        }
+    }
+
+    /// stores a write position kept in a local back into m_arena_write when
+    /// the function that keeps it returns, on every path
+    class arena_write_back
+    {
+      public:
+        arena_write_back(builder& b, char*& w) noexcept
+            : m_builder(b)
+            , m_w(w)
+        {}
+        ~arena_write_back()
+        {
+            m_builder.m_arena_write = m_w;
+        }
+
+        arena_write_back(const arena_write_back&) = delete;
+        arena_write_back& operator=(const arena_write_back&) = delete;
+        arena_write_back(arena_write_back&&) = delete;
+        arena_write_back& operator=(arena_write_back&&) = delete;
+
+      private:
+        builder& m_builder;
+        char*& m_w;
+    };
+
     NLOHMANN_VIEW_ALWAYS_INLINE std::size_t arena_used() const noexcept
     {
         return m_arena_write != nullptr ? static_cast<std::size_t>(m_arena_write - m_doc.arena.data()) : 0;
     }
 
-    NLOHMANN_VIEW_ALWAYS_INLINE void arena_ensure(std::size_t n)
-    {
-        if (NLOHMANN_VIEW_UNLIKELY(static_cast<std::size_t>(m_arena_end - m_arena_write) < n))
-        {
-            arena_grow(n);
-        }
-    }
-
     NLOHMANN_VIEW_NOINLINE void arena_grow(std::size_t n)
     {
         const std::size_t used = arena_used();
@@ -413,25 +548,6 @@ class builder
         m_arena_end = m_doc.arena.data() + m_doc.arena.size();
     }
 
-    /// append the run [r, r + n) to the arena; short runs as one fixed-size
-    /// 16-byte move when both sides have the room (no library call)
-    NLOHMANN_VIEW_ALWAYS_INLINE void arena_run(const unsigned char* r, std::size_t n)
-    {
-        if (n <= 16 && m_end - r >= 16)
-        {
-            arena_ensure(16);
-            std::memcpy(m_arena_write, r, 16);
-        }
-        else if (n != 0)
-        {
-            // (an empty run leaves an empty arena unallocated, and memcpy()
-            // must not be passed its null pointer even for zero bytes)
-            arena_ensure(n);
-            std::memcpy(m_arena_write, r, n);
-        }
-        m_arena_write += n;
-    }
-
     /// UTF-8 encoding of cp at w (room for 4 bytes); returns the position after
     /// it. (A returned pointer stays in a register; writing through a
     /// reference to m_arena_write would store and reload it around every byte.)
@@ -954,11 +1070,11 @@ indent_done:
                 ++p;
             }
             const unsigned char* const int_start = p;
-            if (p != e && *p == '0')
+            if (cur() == '0')
             {
                 ++p;
             }
-            else if (NLOHMANN_VIEW_LIKELY(p != e && *p >= '1' && *p <= '9'))
+            else if (NLOHMANN_VIEW_LIKELY(cur() >= '1' && cur() <= '9'))
             {
                 p = skip_digits(p + 1, e);
             }
@@ -969,7 +1085,7 @@ indent_done:
             const auto int_digits = static_cast<std::size_t>(p - int_start);
             std::size_t frac_digits = 0;
             bool is_float = false;
-            if (p != e && *p == '.')
+            if (cur() == '.')
             {
                 ++p;
                 const unsigned char* const f0 = p;
@@ -982,20 +1098,20 @@ indent_done:
                 is_float = true;
             }
             std::int64_t exponent = 0;
-            if (p != e && (*p | 0x20) == 'e')
+            if ((cur() | 0x20) == 'e')
             {
                 ++p;
                 bool exp_negative = false;
-                if (p != e && (*p == '+' || *p == '-'))
+                if (cur() == '+' || cur() == '-')
                 {
                     exp_negative = *p == '-';
                     ++p;
                 }
-                if (NLOHMANN_VIEW_UNLIKELY(p == e || !is_digit(*p)))
+                if (NLOHMANN_VIEW_UNLIKELY(!is_digit(cur())))
                 {
                     return fail(error_code::number_after_exponent);
                 }
-                while (p != e && is_digit(*p))
+                while (is_digit(cur()))
                 {
                     if (exponent < 100000)
                     {
@@ -1057,7 +1173,7 @@ indent_done:
             ++p; // opening quote
             const unsigned char* const s = p;
             p = scan_string_run<Value>(p, e);
-            if (NLOHMANN_VIEW_LIKELY(p != e && *p == '"'))
+            if (NLOHMANN_VIEW_LIKELY(cur() == '"'))
             {
                 push_node(value_t::string, 0, 0, static_cast<std::size_t>(s - b), static_cast<std::uint64_t>(p - s));
                 ++p;

include/nlohmann/detail/view/edit.hpp

@@ -51,6 +51,11 @@ struct first_true<false, Conditions...> : std::integral_constant < int, 1 + firs
 inline void check_utf8(const char* s, std::size_t n)
 {
     const auto* const p = reinterpret_cast<const unsigned char*>(s); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    const auto hex = [](unsigned char c)
+    {
+        constexpr const char* digits = "0123456789ABCDEF";
+        return std::string{digits[c >> 4u], digits[c & 0xFu]};
+    };
     for (std::size_t i = 0; i < n;)
     {
         const unsigned char c = p[i];
@@ -59,22 +64,39 @@ inline void check_utf8(const char* s, std::size_t n)
             ++i;
             continue;
         }
-        const utf8_sequence_shape shape = utf8_shape(c);
-        const std::size_t len = shape.length;
-        if (len == 0)
+        std::size_t len = 0;
+        unsigned char lo = 0x80;
+        unsigned char hi = 0xBF;
+        if (c >= 0xC2 && c <= 0xDF)
         {
-            throw_type_error(exception_id::invalid_utf8, concat("invalid UTF-8 byte at index ", std::to_string(i), ": 0x", hex_byte(c)));
+            len = 2;
+        }
+        else if (c >= 0xE0 && c <= 0xEF)
+        {
+            len = 3;
+            lo = c == 0xE0 ? 0xA0 : 0x80;
+            hi = c == 0xED ? 0x9F : 0xBF;
+        }
+        else if (c >= 0xF0 && c <= 0xF4)
+        {
+            len = 4;
+            lo = c == 0xF0 ? 0x90 : 0x80;
+            hi = c == 0xF4 ? 0x8F : 0xBF;
+        }
+        else
+        {
+            throw_type_error(316, concat("invalid UTF-8 byte at index ", std::to_string(i), ": 0x", hex(c)));
         }
         for (std::size_t k = 1; k < len; ++k)
         {
             if (i + k == n)
             {
-                throw_type_error(exception_id::invalid_utf8, concat("incomplete UTF-8 string; last byte: 0x", hex_byte(p[n - 1])));
+                throw_type_error(316, concat("incomplete UTF-8 string; last byte: 0x", hex(p[n - 1])));
             }
             const unsigned char b = p[i + k];
-            if (b < (k == 1 ? shape.second_lo : 0x80) || b > (k == 1 ? shape.second_hi : 0xBF))
+            if (b < (k == 1 ? lo : 0x80) || b > (k == 1 ? hi : 0xBF))
             {
-                throw_type_error(exception_id::invalid_utf8, concat("invalid UTF-8 byte at index ", std::to_string(i + k), ": 0x", hex_byte(b)));
+                throw_type_error(316, concat("invalid UTF-8 byte at index ", std::to_string(i + k), ": 0x", hex(b)));
             }
         }
         i += len;
@@ -122,7 +144,7 @@ class editor
         node* const o = own(object);
         if (o->kind != static_cast<std::uint8_t>(value_t::object) && o->kind != static_cast<std::uint8_t>(value_t::null))
         {
-            throw_type_error(exception_id::subscript_wrong_type, "cannot use operator[] with a string argument with ", object.type_name());
+            throw_type_error(305, "cannot use operator[] with a string argument with ", object.type_name());
         }
         check_utf8(key.data(), key.size());
         const encoded e = encode(std::forward<V>(value));
@@ -173,7 +195,7 @@ class editor
         node* const a = own(array);
         if (a->kind != static_cast<std::uint8_t>(value_t::array))
         {
-            throw_type_error(exception_id::subscript_wrong_type, "cannot use operator[] with a numeric argument with ", array.type_name());
+            throw_type_error(305, "cannot use operator[] with a numeric argument with ", array.type_name());
         }
         check_index(idx, a->len);
         const encoded e = encode(std::forward<V>(value));
@@ -190,7 +212,7 @@ class editor
         node* const a = own(array);
         if (a->kind != static_cast<std::uint8_t>(value_t::array) && a->kind != static_cast<std::uint8_t>(value_t::null))
         {
-            throw_type_error(exception_id::push_back_wrong_type, "cannot use push_back() with ", array.type_name());
+            throw_type_error(308, "cannot use push_back() with ", array.type_name());
         }
         const encoded e = encode(std::forward<V>(value));
         if (a->kind == static_cast<std::uint8_t>(value_t::null))
@@ -214,7 +236,7 @@ class editor
         node* const a = own(array);
         if (a->kind != static_cast<std::uint8_t>(value_t::array))
         {
-            throw_type_error(exception_id::insert_wrong_type, "cannot use insert() with ", array.type_name());
+            throw_type_error(309, "cannot use insert() with ", array.type_name());
         }
         check_index(idx, a->len + 1);
         const encoded e = encode(std::forward<V>(value));
@@ -234,7 +256,7 @@ class editor
         node* const o = own(object);
         if (o->kind != static_cast<std::uint8_t>(value_t::object))
         {
-            throw_type_error(exception_id::erase_wrong_type, "cannot use erase() with ", object.type_name());
+            throw_type_error(307, "cannot use erase() with ", object.type_name());
         }
         for (const node* k = nav::first(m_doc, o), *end = nav::end(m_doc, o); k != end; k = document_data::after(k + 1))
         {
@@ -252,7 +274,7 @@ class editor
         node* const a = own(array);
         if (a->kind != static_cast<std::uint8_t>(value_t::array))
         {
-            throw_type_error(exception_id::erase_wrong_type, "cannot use erase() with ", array.type_name());
+            throw_type_error(307, "cannot use erase() with ", array.type_name());
         }
         check_index(idx, a->len);
         node* const h = block_of(m_doc, a, 0);
@@ -275,7 +297,7 @@ class editor
     {
         if (NLOHMANN_VIEW_UNLIKELY(v.m_doc != &m_doc || v.m_node == nullptr))
         {
-            throw_invalid_iterator(exception_id::iterator_from_other_value, "view does not belong to this document");
+            throw_invalid_iterator(202, "view does not belong to this document");
         }
         edit_state_of(m_doc);
         return const_cast<node*>(v.m_node); // NOLINT(cppcoreguidelines-pro-type-const-cast): the nodes belong to this document
@@ -285,7 +307,7 @@ class editor
     {
         if (idx >= limit)
         {
-            throw_array_index_out_of_range(idx);
+            throw_out_of_range(401, concat("array index ", std::to_string(idx), " is out of range"));
         }
     }
 
@@ -426,7 +448,7 @@ class editor
     {
         if (NLOHMANN_VIEW_UNLIKELY(v.m_node == nullptr))
         {
-            throw_type_error(exception_id::type_mismatch, "type must be a value, but is ", "discarded");
+            throw_type_error(302, "type must be a value, but is ", "discarded");
         }
         encoded r;
         if (!is_container(*v.m_node))
@@ -576,7 +598,7 @@ class editor
     {
         if (NLOHMANN_VIEW_UNLIKELY(len >= 0xFFFFFFFFu))
         {
-            throw_out_of_range(exception_id::document_too_large, "strings of 4 GiB or more are not supported by json_document"); // LCOV_EXCL_LINE
+            throw_out_of_range(416, "strings of 4 GiB or more are not supported by json_document"); // LCOV_EXCL_LINE
         }
         node n = plain_node(value_t::string);
         n.flags = static_cast<std::uint8_t>(n.flags | node_flags::edited);
@@ -651,12 +673,12 @@ class editor
                 return string_node(s.data(), s.size());
             }
             case value_t::binary:
-                throw_type_error(exception_id::document_binary_value, "cannot store a binary value in a json_document", "");
+                throw_type_error(319, "cannot store a binary value in a json_document", "");
             case value_t::discarded:
             case value_t::object:
             case value_t::array:
             default:
-                throw_type_error(exception_id::type_mismatch, "type must be a value, but is ", "discarded");
+                throw_type_error(302, "type must be a value, but is ", "discarded");
         }
     }
 

include/nlohmann/detail/view/edit_storage.hpp

@@ -84,7 +84,7 @@ inline std::size_t text_capacity(std::size_t cap, std::size_t used, std::size_t
     constexpr std::size_t limit = 0xFFFFFFFFu;
     if (NLOHMANN_VIEW_UNLIKELY(used > limit || n > limit - used))
     {
-        throw_out_of_range(exception_id::document_too_large, "edits of 4 GiB or more are not supported by json_document");
+        throw_out_of_range(416, "edits of 4 GiB or more are not supported by json_document");
     }
     const std::size_t needed = used + n;
     const std::size_t wanted = needed + (std::min)(limit - needed, std::size_t{256});
@@ -135,7 +135,7 @@ inline void reserve_moved(document_data& d)
     document_data::edit_state& e = edit_state_of(d);
     if (e.moved.size() >= 0xFFFFFFFFu)
     {
-        throw_out_of_range(exception_id::document_too_large, "more than 4294967295 edited arrays and objects are not supported by json_document"); // LCOV_EXCL_LINE
+        throw_out_of_range(416, "more than 4294967295 edited arrays and objects are not supported by json_document"); // LCOV_EXCL_LINE
     }
     if (e.moved.size() == e.moved.capacity() || e.moved_cap.size() == e.moved_cap.capacity())
     {

include/nlohmann/detail/view/errors.hpp

@@ -25,52 +25,32 @@ namespace view
 // Exceptions are thrown out of line, so that the accessors that may throw stay
 // small enough to be inlined.
 
-[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_type_error(exception_id id, const char* prefix, const char* type)
+[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_type_error(int id, const char* prefix, const char* type)
 {
     NLOHMANN_VIEW_THROW(type_error::create(id, concat(prefix, type), nullptr));
 }
 
-[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_type_error(exception_id id, const std::string& msg)
+[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_type_error(int id, const std::string& msg)
 {
     NLOHMANN_VIEW_THROW(type_error::create(id, msg, nullptr));
 }
 
-[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_out_of_range(exception_id id, const std::string& msg)
+[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_out_of_range(int id, const std::string& msg)
 {
     NLOHMANN_VIEW_THROW(out_of_range::create(id, msg, nullptr));
 }
 
-[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_invalid_iterator(exception_id id, const char* msg)
+[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_invalid_iterator(int id, const char* msg)
 {
     NLOHMANN_VIEW_THROW(invalid_iterator::create(id, msg, nullptr));
 }
 
 /// a parse error without a position (as those of json_pointer)
-[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_parse_error(exception_id id, const std::string& msg)
+[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_parse_error(int id, const std::string& msg)
 {
     NLOHMANN_VIEW_THROW(parse_error::create(id, 0, msg, nullptr));
 }
 
-/// out_of_range.401: the array index @a idx is not below the size
-template<typename Index>
-[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_array_index_out_of_range(const Index idx)
-{
-    throw_out_of_range(exception_id::array_index_out_of_range, concat("array index ", std::to_string(idx), " is out of range"));
-}
-
-/// out_of_range.402: the JSON Pointer token '-' of an array of @a size elements
-[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_array_index_past_end(std::size_t size)
-{
-    throw_out_of_range(exception_id::pointer_past_the_end_index, concat("array index '-' (", std::to_string(size), ") is out of range"));
-}
-
-/// out_of_range.403: the object has no member @a key
-template<typename Key>
-[[noreturn]] NLOHMANN_VIEW_NOINLINE void throw_key_not_found(const Key& key)
-{
-    throw_out_of_range(exception_id::key_not_found, concat("key '", key, "' not found"));
-}
-
 /// SAX handler of the error replay: accepts every event without storing it,
 /// and throws the exception the parser reports
 template<typename BasicJsonType>
@@ -169,7 +149,7 @@ template<typename BasicJsonType>
     if (f.code == error_code::input_too_large)
     {
         // (the limit is detail::view::max_input_size(): 4 GiB minus 16 bytes)
-        NLOHMANN_VIEW_THROW(out_of_range::create(exception_id::document_too_large, "input of 4294967280 bytes or more is not supported by json_document", nullptr));
+        NLOHMANN_VIEW_THROW(out_of_range::create(416, "input of 4294967280 bytes or more is not supported by json_document", nullptr));
     }
     throwing_sax<BasicJsonType> sax;
     const bool accepted = BasicJsonType::sax_parse(src, src + size, &sax, input_format_t::json, true, ignore_comments, ignore_trailing_commas);
@@ -189,7 +169,7 @@ template<typename BasicJsonType>
         }
     }
     pos.chars_read_current_line = off + 1 - line_start;
-    NLOHMANN_VIEW_THROW(parse_error::create(exception_id::syntax_error, pos, "syntax error while parsing value", nullptr));
+    NLOHMANN_VIEW_THROW(parse_error::create(101, pos, "syntax error while parsing value", nullptr));
     // LCOV_EXCL_STOP
 }
 

include/nlohmann/detail/view/image.hpp

@@ -186,7 +186,7 @@ inline void compact_nodes(const document_data& d, std::size_t arena_size, std::v
 inline std::vector<std::uint8_t> save_image(const document_data& d)
 {
 #if !NLOHMANN_VIEW_LITTLE_ENDIAN
-    throw_type_error(exception_id::document_image_unsupported, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
+    throw_type_error(320, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
 #endif
     const std::size_t arena_size = d.arena_size;
     std::vector<node> compacted;
@@ -203,7 +203,7 @@ inline std::vector<std::uint8_t> save_image(const document_data& d)
     if (NLOHMANN_VIEW_UNLIKELY(text_size >= image_limit || total_arena >= image_limit || count >= image_limit))
     {
         // LCOV_EXCL_START (4 GiB)
-        throw_out_of_range(exception_id::document_too_large, "images of 4 GiB or more are not supported by json_document");
+        throw_out_of_range(416, "images of 4 GiB or more are not supported by json_document");
         // LCOV_EXCL_STOP
     }
     image_header h{};
@@ -660,7 +660,7 @@ inline bool check_image(const node* nodes, std::size_t count, const unsigned cha
 
 [[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_invalid_image(const char* what)
 {
-    throw_parse_error(exception_id::invalid_document_image, concat("invalid json_document image: ", what));
+    throw_parse_error(116, concat("invalid json_document image: ", what));
 }
 
 /// Read an image into d. The text and the decoded strings stay in the image;
@@ -668,7 +668,7 @@ inline bool check_image(const node* nodes, std::size_t count, const unsigned cha
 inline void load_image(document_data& d, const std::uint8_t* image, std::size_t size, image_check check)
 {
 #if !NLOHMANN_VIEW_LITTLE_ENDIAN
-    throw_type_error(exception_id::document_image_unsupported, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
+    throw_type_error(320, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
 #endif
     if (image == nullptr || size < sizeof(image_header))
     {

include/nlohmann/detail/view/input.hpp

@@ -10,6 +10,9 @@
 
 #include <algorithm> // max
 #include <cstddef> // size_t
+#ifndef JSON_NO_IO
+    #include <cstdio> // FILE, fread
+#endif
 #include <istream> // istream, streambuf
 #include <string> // basic_string, char_traits, string
 #include <type_traits> // decay, integral_constant, is_array, is_const, is_integral, is_lvalue_reference, is_pointer, is_same, remove_cv, remove_extent, remove_pointer, remove_reference
@@ -154,6 +157,37 @@ inline void append_stream(std::string& buf, std::istream& is)
     is.clear(is.rdstate() | std::ios::eofbit);
 }
 
+/// a pointer to a C stream (never with JSON_NO_IO, which leaves out <cstdio>)
+template<typename T>
+struct is_c_stream
+#ifndef JSON_NO_IO
+    : std::is_same<T, std::FILE*>
+#else
+    : std::false_type
+#endif
+{};
+
+#ifndef JSON_NO_IO
+/// append the rest of a C stream: in blocks with fread, not character by
+/// character (the library's file adapter reads with fgetc);
+/// f is not null
+inline void append_file(std::string& buf, std::FILE* f)
+{
+    for (;;)
+    {
+        const std::size_t used = buf.size();
+        const std::size_t room = (std::max)(buf.capacity() - used, std::size_t{4096});
+        buf.resize(used + room);
+        const std::size_t got = std::fread(&buf[used], 1, room, f);
+        buf.resize(used + got);
+        if (got < room)
+        {
+            break; // end of file, or an error (as fgetc, which returns EOF for both)
+        }
+    }
+}
+#endif
+
 }  // namespace view
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/view/iterator.hpp

@@ -110,7 +110,7 @@ class view_iterator
     {
         if (NLOHMANN_VIEW_UNLIKELY(m_value_offset == 0))
         {
-            throw_invalid_iterator(exception_id::iterator_key_not_object, "cannot use key() for non-object iterators");
+            throw_invalid_iterator(207, "cannot use key() for non-object iterators");
         }
         return string_view_t(m_doc->str(*m_pos), m_pos->len);
     }
@@ -147,20 +147,21 @@ class view_item
 
     view_item(const iterator& it, std::size_t index)
         : m_it(it)
-    {
-        if (!it.is_object_iterator())
-        {
-            m_index = std::to_string(index);
-        }
-    }
+        , m_position(index)
+    {}
 
-    /// the member key, or the element index for arrays
+    /// the member key, or the element index for arrays (as text made on the
+    /// first call, so that iterating over the values pays nothing for it)
     string_view_t key() const
     {
         if (m_it.is_object_iterator())
         {
             return m_it.key();
         }
+        if (m_index.empty())
+        {
+            m_index = std::to_string(m_position);
+        }
         return string_view_t(m_index.data(), m_index.size());
     }
 
@@ -183,7 +184,8 @@ class view_item
 
   private:
     iterator m_it;
-    std::string m_index{}; // NOLINT(readability-redundant-member-init)
+    std::size_t m_position; ///< the index of an array element
+    mutable std::string m_index{}; ///< the text of m_position, once key() was called // NOLINT(readability-redundant-member-init)
 };
 
 /// the range returned by basic_json_view::items()

include/nlohmann/detail/view/lookup.hpp

@@ -166,6 +166,10 @@ const node* element_at(const document_data& d, const node* array, std::size_t id
     {
         return e + idx; // a growable block: one link per element
     }
+    if (array->next == array->len + 1u && (!nav::editable() || (array->flags & node_flags::moved) == 0))
+    {
+        return e + idx; // no element has a subtree: the elements are the nodes after the array
+    }
     for (std::size_t i = 0; i < idx; ++i)
     {
         e = document_data::after(e);
@@ -181,6 +185,10 @@ const node* last_child(const document_data& d, const node* container) noexcept
     const std::size_t value_offset = container->kind == static_cast<std::uint8_t>(value_t::object) ? 1 : 0;
     const node* const end = navigation<Editable>::end(d, container);
     const node* last = navigation<Editable>::first(d, container);
+    if (value_offset == 0 && container->next == container->len + 1u && (!navigation<Editable>::editable() || (container->flags & node_flags::moved) == 0))
+    {
+        return last + (container->len - 1u); // an array without subtrees: the elements are the nodes after it
+    }
     for (const node* c = document_data::after(last + value_offset); c != end; c = document_data::after(c + value_offset))
     {
         last = c;

include/nlohmann/detail/view/materialize.hpp

@@ -8,7 +8,7 @@
 
 #pragma once
 
-#include <algorithm> // max
+#include <array> // array
 #include <cstddef> // size_t
 #include <cstdint> // int64_t, uint8_t
 #include <string> // string
@@ -40,12 +40,13 @@ template<typename BasicJsonType, bool Editable>
 BasicJsonType materialize(const document_data& d, const node* n)
 {
     using string_t = typename BasicJsonType::string_t;
-    using sax_t = json_sax_dom_parser<BasicJsonType, iterator_input_adapter<const char*>>;
+    using sax_t = json_sax_dom_parser<BasicJsonType, iterator_input_adapter<const char*>, true>;
     using nav = navigation<Editable>;
 
     // the open containers: their next element (or key of the next member),
-    // their end, and whether they are objects; sized once from the
-    // document's deepest nesting (for a subtree an upper bound)
+    // their end, and whether they are objects; for the first 16 levels on the
+    // stack, else sized once from the document's deepest nesting (for a
+    // subtree an upper bound)
     struct frame
     {
         const node* pos;
@@ -53,10 +54,43 @@ BasicJsonType materialize(const document_data& d, const node* n)
         bool object;
     };
 
+    // a scalar needs neither the handler nor the stack of open containers
+    switch (static_cast<value_t>(n->kind))
+    {
+        case value_t::string:
+            return BasicJsonType(string_t(d.str(*n), n->len));
+        case value_t::number_integer:
+            return BasicJsonType(static_cast<typename BasicJsonType::number_integer_t>(static_cast<std::int64_t>(integer_bits(*n))));
+        case value_t::number_unsigned:
+            return BasicJsonType(static_cast<typename BasicJsonType::number_unsigned_t>(integer_bits(*n)));
+        case value_t::number_float:
+            return BasicJsonType(float_value<typename BasicJsonType::number_float_t>(d, *n));
+        case value_t::boolean:
+            return BasicJsonType((n->flags & node_flags::is_true) != 0);
+        case value_t::null:
+            return BasicJsonType(nullptr);
+        case value_t::object:
+        case value_t::array:
+        case value_t::binary:
+        case value_t::discarded:
+        default:
+            break;
+    }
+
     BasicJsonType result;
     sax_t sax(result, true);
     const string_t no_token{};
-    std::vector<frame> open((std::max)(d.max_depth, std::size_t{1}));
+    // (shallow subtrees on the stack: a call for a small value then allocates only for the value)
+    std::array<frame, 16> shallow; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): filled as containers open
+    std::vector<frame> deep{};
+    frame* open = shallow.data();
+    std::size_t capacity = shallow.size();
+    if (d.max_depth > capacity)
+    {
+        deep.resize(d.max_depth);
+        open = deep.data();
+        capacity = deep.size();
+    }
     std::size_t depth = 0;
     for (;;)
     {
@@ -76,9 +110,13 @@ BasicJsonType materialize(const document_data& d, const node* n)
                 {
                     sax.start_array(n->len);
                 }
-                if (NLOHMANN_VIEW_UNLIKELY(depth == open.size()))
+                if (NLOHMANN_VIEW_UNLIKELY(depth == capacity))
                 {
-                    open.resize(depth * 2); // (deeper than the recorded nesting, e.g. after edits)
+                    // (deeper than the recorded nesting, e.g. after edits)
+                    deep.assign(open, open + depth);
+                    deep.resize(depth * 2);
+                    open = deep.data();
+                    capacity = deep.size();
                 }
                 open[depth++] = frame{nav::first(d, n), nav::end(d, n), object};
                 break;

include/nlohmann/detail/view/object_index.hpp

@@ -47,27 +47,96 @@ constexpr std::size_t index_max_displacement = 64;
 static_assert(document_data::index_min_members >= 2 * index_max_displacement,
               "a table must be much larger than the probe window of a lookup");
 
-/// hash of a key: its bytes, eight at a time, in a fixed byte order
+/// hash of a key: its bytes, eight at a time (in a fixed byte order), where the
+/// last word may overlap the one before (so that no loop over single bytes is
+/// needed); a key of fewer than eight bytes is read as two overlapping words of
+/// four or two bytes (in the native byte order: the hash is not stored, and the
+/// same on both sides of a lookup)
 inline std::uint64_t key_hash(const char* s, std::size_t n) noexcept
 {
     std::uint64_t h = 0x9E3779B97F4A7C15u * (n + 1);
     const auto* p = reinterpret_cast<const unsigned char*>(s); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-    while (n >= 8)
+    std::uint64_t w = 0;
+    if (n >= 8)
+    {
+        const unsigned char* const last = p + n - 8;
+        while (p < last)
         {
             h = (h ^ read_eight_bytes(p)) * 0xBF58476D1CE4E5B9u;
             h ^= h >> 29u;
             p += 8;
-        n -= 8;
         }
-    std::uint64_t w = 0;
-    for (std::size_t i = 0; i < n; ++i)
+        w = read_eight_bytes(last);
+    }
+    else if (n >= 4)
     {
-        w |= static_cast<std::uint64_t>(p[i]) << (8u * i);
+        std::uint32_t head = 0;
+        std::uint32_t tail = 0;
+        std::memcpy(&head, p, 4);
+        std::memcpy(&tail, p + n - 4, 4);
+        w = static_cast<std::uint64_t>(head) | (static_cast<std::uint64_t>(tail) << 32u);
     }
-    h = (h ^ w) * 0x94D049BB133111EBu;
+    else if (n >= 2)
+    {
+        std::uint16_t head = 0;
+        std::uint16_t tail = 0;
+        std::memcpy(&head, p, 2);
+        std::memcpy(&tail, p + n - 2, 2);
+        w = static_cast<std::uint64_t>(head) | (static_cast<std::uint64_t>(tail) << 16u);
+    }
+    else if (n == 1)
+    {
+        w = p[0];
+    }
+    // (a product only carries bits upwards, and the slot is taken from the low
+    // bits: the high bits of the last word are folded down before the multiplication)
+    h = (h ^ w ^ (w >> 29u)) * 0x94D049BB133111EBu;
     return h ^ (h >> 31u);
 }
 
+/// whether the n <= 16 bytes at a and b are equal, as two overlapping words
+/// (the first and the last 8, 4, or 2 bytes) and without a call
+NLOHMANN_VIEW_ALWAYS_INLINE bool same_short_bytes(const unsigned char* a, const unsigned char* b, std::size_t n) noexcept
+{
+    if (n >= 8)
+    {
+        std::uint64_t x0 = 0;
+        std::uint64_t x1 = 0;
+        std::uint64_t y0 = 0;
+        std::uint64_t y1 = 0;
+        std::memcpy(&x0, a, 8);
+        std::memcpy(&x1, a + n - 8, 8);
+        std::memcpy(&y0, b, 8);
+        std::memcpy(&y1, b + n - 8, 8);
+        return x0 == y0 && x1 == y1;
+    }
+    if (n >= 4)
+    {
+        std::uint32_t x0 = 0;
+        std::uint32_t x1 = 0;
+        std::uint32_t y0 = 0;
+        std::uint32_t y1 = 0;
+        std::memcpy(&x0, a, 4);
+        std::memcpy(&x1, a + n - 4, 4);
+        std::memcpy(&y0, b, 4);
+        std::memcpy(&y1, b + n - 4, 4);
+        return x0 == y0 && x1 == y1;
+    }
+    if (n >= 2)
+    {
+        std::uint16_t x0 = 0;
+        std::uint16_t x1 = 0;
+        std::uint16_t y0 = 0;
+        std::uint16_t y1 = 0;
+        std::memcpy(&x0, a, 2);
+        std::memcpy(&x1, a + n - 2, 2);
+        std::memcpy(&y0, b, 2);
+        std::memcpy(&y1, b + n - 2, 2);
+        return x0 == y0 && x1 == y1;
+    }
+    return n == 0 || *a == *b;
+}
+
 /// build the table of a large object
 inline void build_object_index(document_data& d, node* obj)
 {
@@ -132,6 +201,27 @@ inline const node* find_indexed(const document_data& d, const node* obj, const c
     const document_data::object_index& ix = d.indexes[obj->extra - 1u];
     const std::uint32_t* const table = d.index_slots.data() + ix.start;
     std::size_t slot = conditional_static_cast<std::size_t>(key_hash(key, n)) & ix.mask;
+    const auto* const k_bytes = reinterpret_cast<const unsigned char*>(key); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    // (the loop for longer keys comes first, as the code is laid out; it is not the more common case)
+    if (NLOHMANN_VIEW_UNLIKELY(n <= 16))
+    {
+        // (up to 16 bytes, the bytes are compared as two words, without a call)
+        for (std::size_t distance = 0; distance <= index_max_displacement; ++distance)
+        {
+            const std::uint32_t s = table[slot];
+            if (s == 0)
+            {
+                return nullptr;
+            }
+            const node* const k = obj + s;
+            if (k->len == n && same_short_bytes(reinterpret_cast<const unsigned char*>(d.str(*k)), k_bytes, n)) // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+            {
+                return k;
+            }
+            slot = (slot + 1) & ix.mask;
+        }
+        return nullptr;
+    }
     for (std::size_t distance = 0; distance <= index_max_displacement; ++distance)
     {
         const std::uint32_t s = table[slot];

include/nlohmann/detail/view/pointer.hpp

@@ -32,15 +32,51 @@ enum class pointer_mode
     contains,  ///< as basic_json::contains(): no exceptions at all
 };
 
-/// the outcome of reading an array index: detail::parse_array_index(), shared with json_pointer
-using index_status = detail::array_index_status;
+/// the outcome of reading an array index from a reference token
+enum class index_status
+{
+    ok,
+    leading_zero, ///< parse_error.106
+    not_number,   ///< parse_error.109
+    unresolved,   ///< out_of_range.404
+    too_large,    ///< out_of_range.410
+};
 
 /// reads an array index like json_pointer::array_index (RFC 6901, Sect. 4),
 /// but reports errors instead of throwing them
 template<typename StringType>
 index_status array_index(const StringType& s, std::size_t& idx) noexcept
 {
-    return detail::parse_array_index(s, idx);
+    // as basic_json: the empty token and "-" (past the last element) are
+    // unresolved rather than not a number
+    if (s.empty() || (s.size() == 1 && s[0] == '-'))
+    {
+        return index_status::unresolved;
+    }
+    if (s[0] < '0' || s[0] > '9')
+    {
+        return index_status::not_number;
+    }
+    if (s.size() > 1 && s[0] == '0')
+    {
+        return index_status::leading_zero;
+    }
+    std::uint64_t v = 0;
+    for (const auto c : s)
+    {
+        const auto d = static_cast<unsigned>(static_cast<unsigned char>(c)) - '0';
+        if (d > 9 || v > ((std::numeric_limits<std::uint64_t>::max)() - d) / 10)
+        {
+            return index_status::unresolved; // not a number, or beyond unsigned long long
+        }
+        v = (v * 10) + d;
+    }
+    if (v >= (std::numeric_limits<std::size_t>::max)()) // (std::size_t converts to std::uint64_t implicitly)
+    {
+        return index_status::too_large;
+    }
+    idx = static_cast<std::size_t>(v);
+    return index_status::ok;
 }
 
 /// throws the exception json_pointer::array_index throws for this status
@@ -50,15 +86,15 @@ template<typename StringType>
     switch (status)
     {
         case index_status::leading_zero:
-            throw_parse_error(exception_id::pointer_index_leading_zero, concat("array index '", s, "' must not begin with '0'"));
-        case index_status::not_a_number:
-            throw_parse_error(exception_id::pointer_index_not_a_number, concat("array index '", s, "' is not a number"));
-        case index_status::exceeds_size_type:
-            throw_out_of_range(exception_id::value_out_of_range, concat("array index ", s, " exceeds size_type")); // LCOV_EXCL_LINE
+            throw_parse_error(106, concat("array index '", s, "' must not begin with '0'"));
+        case index_status::not_number:
+            throw_parse_error(109, concat("array index '", s, "' is not a number"));
+        case index_status::too_large:
+            throw_out_of_range(410, concat("array index ", s, " exceeds size_type")); // LCOV_EXCL_LINE
         case index_status::unresolved:
         case index_status::ok:
         default:
-            throw_out_of_range(exception_id::pointer_unresolved, concat("unresolved reference token '", s, "'"));
+            throw_out_of_range(404, concat("unresolved reference token '", s, "'"));
     }
 }
 
@@ -83,7 +119,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
             {
                 if (mode == pointer_mode::checked)
                 {
-                    throw_key_not_found(token);
+                    throw_out_of_range(403, concat("key '", token, "' not found"));
                 }
                 return View();
             }
@@ -95,7 +131,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
             {
                 if (throwing)
                 {
-                    throw_array_index_past_end(cur.size());
+                    throw_out_of_range(402, concat("array index '-' (", std::to_string(cur.size()), ") is out of range"));
                 }
                 return View();
             }
@@ -103,7 +139,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
             const index_status status = array_index(token, idx);
             if (status != index_status::ok)
             {
-                const bool parse_error = status == index_status::leading_zero || status == index_status::not_a_number;
+                const bool parse_error = status == index_status::leading_zero || status == index_status::not_number;
                 if (throwing || (mode == pointer_mode::value && parse_error))
                 {
                     throw_array_index_error(status, token);
@@ -114,7 +150,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
             {
                 if (mode == pointer_mode::checked)
                 {
-                    throw_array_index_out_of_range(idx);
+                    throw_out_of_range(401, concat("array index ", std::to_string(idx), " is out of range"));
                 }
                 return View();
             }
@@ -124,7 +160,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
         {
             if (throwing)
             {
-                throw_out_of_range(exception_id::pointer_unresolved, concat("unresolved reference token '", token, "'"));
+                throw_out_of_range(404, concat("unresolved reference token '", token, "'"));
             }
             return View();
         }

include/nlohmann/detail/view/serializer.hpp

@@ -23,6 +23,7 @@
 #include <nlohmann/detail/view/macro_scope.hpp>
 #include <nlohmann/detail/view/node.hpp>
 #include <nlohmann/detail/view/number.hpp>
+#include <nlohmann/detail/view/simd.hpp>
 
 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -80,13 +81,6 @@ class output_buffer
         put(s, N - 1);
     }
 
-    void put_repeated(char c, std::size_t n)
-    {
-        reserve(n);
-        std::memset(m_pos, c, n);
-        m_pos += n;
-    }
-
     /// the write position and the end of the writable space, for a writer
     /// that keeps the position in a local variable (set_cursor() hands it back)
     char* cursor() const noexcept
@@ -143,9 +137,27 @@ class output_buffer
 /// image_check::bounds can have others, which are then written unchanged).
 inline std::size_t plain_output_run(const unsigned char* s, std::size_t n) noexcept
 {
+    std::size_t i = 0;
+#if NLOHMANN_VIEW_SSE2
+    // (16 bytes per step; with NEON, the mask of a step costs more than it saves on the
+    // short runs that are typical here)
+    // NOLINTBEGIN(portability-simd-intrinsics)
+    for (; i + 16 <= n; i += 16)
+    {
+        const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(s + i))); // NOLINT(bugprone-casting-through-void)
+        // (a byte is below 0x20 if it is its own minimum with 0x1F)
+        const __m128i special = _mm_or_si128(_mm_or_si128(_mm_cmpeq_epi8(in, _mm_set1_epi8('"')), _mm_cmpeq_epi8(in, _mm_set1_epi8('\\'))),
+                                             _mm_cmpeq_epi8(_mm_min_epu8(in, _mm_set1_epi8(0x1F)), in));
+        const auto mask = static_cast<std::uint64_t>(static_cast<unsigned>(_mm_movemask_epi8(special)));
+        if (mask != 0)
+        {
+            return i + static_cast<std::size_t>(count_trailing_zeros(mask));
+        }
+    }
+    // NOLINTEND(portability-simd-intrinsics)
+#endif
     constexpr std::uint64_t ones = 0x0101010101010101ull;
     constexpr std::uint64_t high = 0x8080808080808080ull;
-    std::size_t i = 0;
     for (; i + 8 <= n; i += 8)
     {
         const std::uint64_t v = read_eight_bytes(s + i);
@@ -196,6 +208,70 @@ inline bool is_ascii_without_delete(const char* s, std::size_t n) noexcept
     return true;
 }
 
+#if NLOHMANN_VIEW_VECTOR
+/// the bytes of the 16 at p that ensure_ascii cannot copy (a quote, a
+/// backslash, a control character, DEL, or not ASCII; a signed compare with
+/// 0x20 finds control characters and non-ASCII bytes at once), one bit per
+/// byte (x86) or one nibble per byte (NEON)
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t ascii_stop_mask(const unsigned char* p) noexcept
+{
+#if NLOHMANN_VIEW_NEON
+    const uint8x16_t in = vld1q_u8(p);
+    const uint8x16_t special = vorrq_u8(vorrq_u8(vceqq_u8(in, vdupq_n_u8('"')), vceqq_u8(in, vdupq_n_u8('\\'))),
+                                        vorrq_u8(vceqq_u8(in, vdupq_n_u8(0x7F)), vcltq_s8(vreinterpretq_s8_u8(in), vdupq_n_s8(0x20))));
+    return vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(special), 4)), 0);
+#else
+    const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
+    const __m128i special = _mm_or_si128(_mm_or_si128(_mm_cmpeq_epi8(in, _mm_set1_epi8('"')), _mm_cmpeq_epi8(in, _mm_set1_epi8('\\'))),
+                                         _mm_or_si128(_mm_cmpeq_epi8(in, _mm_set1_epi8(0x7F)), _mm_cmplt_epi8(in, _mm_set1_epi8(0x20))));
+    return static_cast<std::uint64_t>(static_cast<unsigned>(_mm_movemask_epi8(special)));
+#endif
+}
+
+/// the width in bits of a byte in the mask of ascii_stop_mask()
+constexpr unsigned ascii_stop_bits() noexcept
+{
+    return NLOHMANN_VIEW_NEON ? 4u : 1u;
+}
+#endif
+
+/// As find_ascii_copyable_run(), 16 bytes per step. end is the end of the
+/// buffer that holds the n bytes at p (a short run is read as 16 bytes if
+/// they are in the buffer).
+inline std::size_t ascii_copyable_run(const unsigned char* p, std::size_t n, const unsigned char* end) noexcept
+{
+#if NLOHMANN_VIEW_VECTOR
+    if (n >= 16)
+    {
+        std::size_t i = 0;
+        for (; i + 16 <= n; i += 16)
+        {
+            const std::uint64_t mask = ascii_stop_mask(p + i);
+            if (mask != 0)
+            {
+                return i + (static_cast<std::size_t>(count_trailing_zeros(mask)) / ascii_stop_bits());
+            }
+        }
+        if (i == n)
+        {
+            return n;
+        }
+        // the last 16 bytes: those before i are known to be copyable
+        const std::uint64_t mask = ascii_stop_mask(p + n - 16);
+        return mask != 0 ? n - 16 + (static_cast<std::size_t>(count_trailing_zeros(mask)) / ascii_stop_bits()) : n;
+    }
+    if (end - p >= 16)
+    {
+        // (the bytes after the run are masked out)
+        const std::uint64_t mask = ascii_stop_mask(p) & ((std::uint64_t{1} << (n * ascii_stop_bits())) - 1u);
+        return mask != 0 ? static_cast<std::size_t>(count_trailing_zeros(mask)) / ascii_stop_bits() : n;
+    }
+#else
+    static_cast<void>(end);
+#endif
+    return find_ascii_copyable_run(p, n);
+}
+
 /// A stack that starts in a buffer of the caller (a local array) and moves to
 /// the heap (a vector of the caller) only when that is full, so that dumps of
 /// shallow documents need no allocation. The top is a pointer, as in
@@ -275,6 +351,39 @@ NLOHMANN_VIEW_ALWAYS_INLINE char* put_literal(char* w, const char (&s)[N]) noexc
     return w + N - 1;
 }
 
+/// the depth of the innermost open container, counted only for indented output
+template<bool Counted>
+struct depth_counter
+{
+    std::size_t value = 0;
+    void enter() noexcept
+    {
+        ++value;
+    }
+    std::size_t leave() noexcept
+    {
+        return --value;
+    }
+    std::size_t get() const noexcept
+    {
+        return value;
+    }
+};
+
+template<>
+struct depth_counter<false>
+{
+    void enter() noexcept {}
+    std::size_t leave() noexcept // NOLINT(readability-convert-member-functions-to-static): same interface as depth_counter<true>
+    {
+        return 0;
+    }
+    std::size_t get() const noexcept // NOLINT(readability-convert-member-functions-to-static): same interface as depth_counter<true>
+    {
+        return 0;
+    }
+};
+
 /// how the view's dump() writes a value
 struct dump_style
 {
@@ -310,140 +419,96 @@ class view_serializer
     {}
 
     void dump(const node* root)
-    {
-        if (!m_style.pretty)
     {
         if (m_style.ensure_ascii)
         {
-                dump_compact_ascii(root);
+            dump_ascii(root);
+        }
+        else if (m_style.pretty)
+        {
+            dump_pretty(root);
         }
         else if (m_style.source_numbers)
         {
-                dump_compact<true, false>(root);
+            dump_text<true, false, false>(root);
         }
         else
         {
-                dump_compact<false, false>(root);
-            }
-            return;
-        }
-        struct frame
-        {
-            const node* pos; ///< next element, or key of the next member
-            const node* end;
-            bool object;
-            bool first;  ///< nothing written yet
-        };
-        std::array<frame, 32> buffer; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-        std::vector<frame> heap;
-        small_stack<frame> stack(buffer.data(), buffer.size(), heap);
-        const node* n = root;
-        for (;;)
-        {
-            // write the value at n
-            if (is_container(*n))
-            {
-                const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
-                if (n->len == 0)
-                {
-                    m_out.put(object ? "{}" : "[]", 2);
-                }
-                else
-                {
-                    m_out.put(object ? '{' : '[');
-                    stack.push_back(frame{nav::first(m_doc, n), nav::end(m_doc, n), object, true});
-                }
-            }
-            else
-            {
-                write_scalar(*n);
-            }
-
-            // go to the next value: close finished containers, then separate
-            for (;;)
-            {
-                if (stack.empty())
-                {
-                    m_out.finish();
-                    return;
-                }
-                if (stack.back().pos == stack.back().end)
-                {
-                    const bool object = stack.back().object;
-                    stack.pop_back();
-                    newline(stack.size());
-                    m_out.put(object ? '}' : ']');
-                    continue;
-                }
-                frame& f = stack.back();
-                if (!f.first)
-                {
-                    m_out.put(',');
-                }
-                f.first = false;
-                newline(stack.size());
-                if (f.object)
-                {
-                    write_string(*f.pos);
-                    if (m_style.pretty)
-                    {
-                        m_out.put(": ");
-                    }
-                    else
-                    {
-                        m_out.put(':');
-                    }
-                    n = nav::value(f.pos + 1);
-                    f.pos = document_data::after(f.pos + 1);
-                }
-                else
-                {
-                    n = nav::value(f.pos);
-                    f.pos = document_data::after(f.pos);
-                }
-                break;
-            }
+            dump_text<false, false, false>(root);
         }
     }
 
   private:
+    /// dump_text() with ensure_ascii, out of line: the walk without it is
+    /// faster when it is not merged with this one into dump()
+    NLOHMANN_VIEW_NOINLINE void dump_ascii(const node* root)
+    {
+        if (m_style.pretty)
+        {
+            if (m_style.source_numbers)
+            {
+                dump_text<true, true, true>(root);
+            }
+            else
+            {
+                dump_text<false, true, true>(root);
+            }
+        }
+        else if (m_style.source_numbers)
+        {
+            dump_text<true, false, true>(root);
+        }
+        else
+        {
+            dump_text<false, false, true>(root);
+        }
+    }
+
+    /// dump_text() with indentation, out of line: the compact walk is faster
+    /// when it is not merged with the indented ones into dump()
+    NLOHMANN_VIEW_NOINLINE void dump_pretty(const node* root)
+    {
+        if (m_style.source_numbers)
+        {
+            dump_text<true, true, false>(root);
+        }
+        else
+        {
+            dump_text<false, true, false>(root);
+        }
+    }
+
     /// a string that is not a plain string of the source (decoded, or written
     /// by an edit), without ensure_ascii: runs without characters to escape
-    /// are copied
-    NLOHMANN_VIEW_NOINLINE void write_decoded(const node& n)
+    /// are copied. If validate is set, the string must be valid UTF-8: the
+    /// runs are found by the lexer's scan, which validates the sequences, and
+    /// invalid UTF-8 throws what basic_json::dump() throws. (The compact output
+    /// writes the bytes of a damaged image unchanged, and scans without
+    /// validating them.)
+    NLOHMANN_VIEW_NOINLINE void write_decoded(const node& n, bool validate)
     {
         const auto* const s = reinterpret_cast<const unsigned char*>(m_doc.str(n)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
         m_out.put('"');
         for (std::size_t i = 0; i < n.len;)
         {
-            const std::size_t run = plain_output_run(s + i, n.len - i);
+            const std::size_t run = validate ? string_bulk_run(s + i, n.len - i) : plain_output_run(s + i, n.len - i);
             if (run != 0)
             {
                 m_out.put(reinterpret_cast<const char*>(s + i), run); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
                 i += run;
                 continue;
             }
+            if (validate && s[i] >= 0x80)
+            {
+                invalid_utf8(s, n.len); // (the scan stopped at ill-formed UTF-8)
+            }
             write_codepoint<false>(s[i], s + i, 1); // a quote, a backslash, or a control character
             ++i;
         }
         m_out.put('"');
     }
 
-    /// dump_compact() with ensure_ascii, out of line: the walk without it is
-    /// faster when it is not merged with this one into dump()
-    NLOHMANN_VIEW_NOINLINE void dump_compact_ascii(const node* root)
-    {
-        if (m_style.source_numbers)
-        {
-            dump_compact<true, true>(root);
-        }
-        else
-        {
-            dump_compact<false, true>(root);
-        }
-    }
-
-    /// whether dump_compact() copies a string or key from the source: one of
+    /// whether dump_text() copies a string or key from the source: one of
     /// the source, and with ensure_ascii one without bytes >= 0x7F (an overload
     /// each, so that the walk without ensure_ascii is compiled exactly as
     /// before: with GCC, a condition that only folds away later changed its
@@ -458,13 +523,155 @@ class view_serializer
         return (n.flags & node_flags::storage) == 0 && is_ascii_without_delete(src + n.off, n.len);
     }
 
-    /// a string with ensure_ascii (dump_compact()), out of line
-    NLOHMANN_VIEW_NOINLINE void write_ascii_string(const node& n)
+    /*!
+    @brief a string with ensure_ascii: the characters that are not printable ASCII as \\uXXXX
+    (a character beyond U+FFFF as a surrogate pair); strings of a document
+    are valid UTF-8, except in a damaged image loaded with image_check::bounds,
+    for which this throws what basic_json::dump() throws for the string
+    */
+    NLOHMANN_VIEW_NOINLINE void write_ascii(const node& n)
     {
-        write_string(n);
+        const auto* const s = reinterpret_cast<const unsigned char*>(m_doc.str(n)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+        const std::size_t size = n.len;
+        char* w = m_out.cursor();
+        char* lim = m_out.limit();
+        // room for k bytes
+        const auto room = [&](std::size_t k)
+        {
+            const auto left = static_cast<std::size_t>(lim - w);
+            if (NLOHMANN_VIEW_UNLIKELY(left < k))
+            {
+                m_out.set_cursor(w);
+                m_out.reserve(k);
+                w = m_out.cursor();
+                lim = m_out.limit();
+            }
+        };
+        static constexpr const char* hex = "0123456789abcdef";
+        // \\uXXXX
+        const auto u_escape = [&](std::uint32_t u)
+        {
+            w[0] = '\\';
+            w[1] = 'u';
+            w[2] = hex[(u >> 12u) & 0xFu];
+            w[3] = hex[(u >> 8u) & 0xFu];
+            w[4] = hex[(u >> 4u) & 0xFu];
+            w[5] = hex[u & 0xFu];
+            w += 6;
+        };
+        room(1);
+        *w++ = '"';
+        std::size_t i = 0;
+        // (a string of the source starts with a run that has nothing to escape, 16 bytes per step)
+        const std::size_t prefix = (n.flags & node_flags::storage) == 0 ? ascii_copyable_run(s, size, reinterpret_cast<const unsigned char*>(m_doc.src + m_doc.size)) : 0; // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+        if (prefix != 0)
+        {
+            room(prefix);
+            std::memcpy(w, s, prefix);
+            w += prefix;
+            i = prefix;
+        }
+        while (i < size)
+        {
+            // (a character that needs an escape sequence is not worth a call)
+            const std::size_t run = is_ascii_copyable(s[i]) ? find_ascii_copyable_run(s + i, size - i) : 0;
+            if (run != 0)
+            {
+                room(run);
+                std::memcpy(w, s + i, run);
+                w += run;
+                i += run;
+                continue;
+            }
+            room(12);
+            if (s[i] >= 0x80)
+            {
+                const unsigned char lead = s[i];
+                // (the two-byte sequences of Latin text and the three-byte sequences of most other
+                // text, with continuation bytes of any value: the ranges that are restricted (E0,
+                // ED, and the sequences of four bytes) go through validate_one_utf8())
+                if (lead >= 0xE1 && lead <= 0xEF && lead != 0xED && size - i >= 3 && (s[i + 1] & 0xC0u) == 0x80 && (s[i + 2] & 0xC0u) == 0x80)
+                {
+                    u_escape(((lead & 0x0Fu) << 12u) | ((s[i + 1] & 0x3Fu) << 6u) | (s[i + 2] & 0x3Fu));
+                    i += 3;
+                    continue;
+                }
+                if (lead >= 0xC2 && lead <= 0xDF && size - i >= 2 && (s[i + 1] & 0xC0u) == 0x80)
+                {
+                    u_escape(((lead & 0x1Fu) << 6u) | (s[i + 1] & 0x3Fu));
+                    i += 2;
+                    continue;
+                }
+                const std::size_t len = validate_one_utf8(s + i, size - i);
+                if (NLOHMANN_VIEW_UNLIKELY(len == 0))
+                {
+                    m_out.set_cursor(w);
+                    invalid_utf8(s, size);
+                    return; // LCOV_EXCL_LINE (invalid_utf8 throws)
+                }
+                std::uint32_t codepoint = s[i] & (0xFFu >> (len + 1));
+                for (std::size_t k = 1; k < len; ++k)
+                {
+                    codepoint = (codepoint << 6u) | (s[i + k] & 0x3Fu);
+                }
+                i += len;
+                if (codepoint <= 0xFFFF)
+                {
+                    u_escape(codepoint);
+                }
+                else
+                {
+                    u_escape(0xD7C0u + (codepoint >> 10u));
+                    u_escape(0xDC00u + (codepoint & 0x3FFu));
+                }
+                continue;
+            }
+            // a quote, a backslash, or a control character (or DEL)
+            const unsigned char c = s[i++];
+            char escape = 0;
+            switch (c)
+            {
+                case 0x08:
+                    escape = 'b';
+                    break;
+                case 0x09:
+                    escape = 't';
+                    break;
+                case 0x0A:
+                    escape = 'n';
+                    break;
+                case 0x0C:
+                    escape = 'f';
+                    break;
+                case 0x0D:
+                    escape = 'r';
+                    break;
+                case 0x22:
+                    escape = '"';
+                    break;
+                case 0x5C:
+                    escape = '\\';
+                    break;
+                default:
+                    break;
+            }
+            if (escape != 0)
+            {
+                w[0] = '\\';
+                w[1] = escape;
+                w += 2;
+            }
+            else
+            {
+                u_escape(c);
+            }
+        }
+        room(1);
+        *w++ = '"';
+        m_out.set_cursor(w);
     }
 
-    /// the copies of dump_compact() that are not fixed-size moves (long
+    /// the copies of dump_text() that are not fixed-size moves (long
     /// strings, or near the end of the source); out of line, so that the
     /// compiler does not merge the fixed-size moves into this call
     NLOHMANN_VIEW_NOINLINE static void copy_long(char* to, const char* from, std::size_t n) noexcept
@@ -481,7 +688,7 @@ class view_serializer
     }
 
     /*!
-    @brief the compact output (the default dump(), or with ensure_ascii)
+    @brief the output, compact (the default dump()) or indented, with or without ensure_ascii
 
     The same walk as dump(), with the write position in a local variable
     (stores through char pointers would otherwise force a reload of the
@@ -489,11 +696,11 @@ class view_serializer
     the source copied by fixed-size moves of 32 bytes where the source has
     that many bytes left, instead of a library call per token. The buffer
     keeps 64 bytes of slack for the overshoot. With ensure_ascii (Ascii), a
-    string of the source is copied only if it has no byte >= 0x7F (see
-    is_ascii_without_delete()); any other string is written by write_string().
+    string of the source is copied only if it has nothing to escape (see
+    copied()); any other string is written by write_ascii().
     */
-    template<bool SourceNumbers, bool Ascii>
-    void dump_compact(const node* root)
+    template<bool SourceNumbers, bool Pretty, bool Ascii>
+    void dump_text(const node* root)
     {
         struct frame
         {
@@ -508,6 +715,16 @@ class view_serializer
         const char* const src_end = src + m_doc.size;
         char* w = m_out.cursor();
         char* lim = m_out.limit();
+        // (indented output) a line break and 63 indentation characters, from
+        // which the line break of a level of up to 63 characters is a copy
+        std::array<char, 64> ruler; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): filled below if used
+        if (Pretty)
+        {
+            ruler.fill(m_style.indent_char);
+            ruler[0] = '\n';
+        }
+        const std::size_t indent = m_style.indent;
+        depth_counter<Pretty> level; // depth of the innermost open container (indented output)
         // room for n bytes and the slack
         const auto room = [&](std::size_t n)
         {
@@ -539,6 +756,22 @@ class view_serializer
             }
             w += n;
         };
+        // (indented output) the line break and the indentation of a level
+        const auto newline = [&](std::size_t depth)
+        {
+            const std::size_t count = 1 + (depth * indent);
+            room(count);
+            if (count <= ruler.size())
+            {
+                std::memcpy(w, ruler.data(), ruler.size());
+            }
+            else
+            {
+                *w = '\n';
+                std::memset(w + 1, m_style.indent_char, count - 1);
+            }
+            w += count;
+        };
         // a string that is not a plain string of the source (out of line, so
         // that the cursor stays in a register here)
         const auto escaped = [&](const node & n)
@@ -546,11 +779,11 @@ class view_serializer
             m_out.set_cursor(w);
             if (enabled(Ascii))
             {
-                write_ascii_string(n);
+                write_ascii(n);
             }
             else
             {
-                write_decoded(n);
+                write_decoded(n, Pretty);
             }
             w = m_out.cursor();
             lim = m_out.limit();
@@ -651,6 +884,7 @@ class view_serializer
                     {
                         *w++ = object ? '{' : '[';
                         stack.push_back(cur);
+                        level.enter();
                         if (Editable)
                         {
                             cur = frame{nav::first(m_doc, n), nav::end(m_doc, n), object};
@@ -693,6 +927,10 @@ class view_serializer
                     {
                         break;
                     }
+                    if (Pretty)
+                    {
+                        newline(level.leave());
+                    }
                     room(1);
                     *w++ = cur.object ? '}' : ']';
                     cur = stack.back();
@@ -701,13 +939,17 @@ class view_serializer
                 room(1);
                 *w++ = ',';
             }
+            if (Pretty)
+            {
+                newline(level.get());
+            }
             const node* const at = Editable ? cur.pos : n;
             if (cur.object)
             {
                 const node& key = *at;
                 if (copied(key, src, std::integral_constant<bool, Ascii>()))
                 {
-                    room(key.len + 3);
+                    room(key.len + (Pretty ? 4 : 3));
                     *w++ = '"';
                     copy(src + key.off, key.len);
                     w[0] = '"';
@@ -717,9 +959,13 @@ class view_serializer
                 else
                 {
                     escaped(key);
-                    room(1);
+                    room(Pretty ? 2 : 1);
                     *w++ = ':';
                 }
+                if (Pretty)
+                {
+                    *w++ = ' ';
+                }
                 if (Editable)
                 {
                     n = nav::value(at + 1);
@@ -738,69 +984,6 @@ class view_serializer
         }
     }
 
-    void newline(std::size_t level)
-    {
-        if (m_style.pretty)
-        {
-            m_out.put('\n');
-            m_out.put_repeated(m_style.indent_char, level * m_style.indent);
-        }
-    }
-
-    void write_scalar(const node& n)
-    {
-        switch (static_cast<value_t>(n.kind))
-        {
-            case value_t::null:
-                m_out.put("null");
-                break;
-            case value_t::boolean:
-                if ((n.flags & node_flags::is_true) != 0)
-                {
-                    m_out.put("true");
-                }
-                else
-                {
-                    m_out.put("false");
-                }
-                break;
-            case value_t::string:
-                write_string(n);
-                break;
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            {
-                const char* const token = m_doc.str(n);
-                const std::uint32_t len = number_length(n);
-                if (!m_style.source_numbers && len == 2 && token[0] == '-' && token[1] == '0')
-                {
-                    m_out.put('0'); // parse() reads -0 as the integer 0
-                }
-                else
-                {
-                    m_out.put(token, len);
-                }
-                break;
-            }
-            case value_t::number_float:
-                if (m_style.source_numbers && (n.flags & node_flags::storage) != node_flags::edited)
-                {
-                    m_out.put(m_doc.str(n), n.len); // (a float set by an edit is written as with shortest)
-                }
-                else
-                {
-                    write_float_node(n);
-                }
-                break;
-            case value_t::object:    // LCOV_EXCL_LINE (containers are written by dump())
-            case value_t::array:     // LCOV_EXCL_LINE
-            case value_t::binary:    // LCOV_EXCL_LINE (not in a document)
-            case value_t::discarded: // LCOV_EXCL_LINE
-            default:                 // LCOV_EXCL_LINE
-                break;               // LCOV_EXCL_LINE
-        }
-    }
-
     /// a float node as dump() writes it
     void write_float_node(const node& n)
     {
@@ -890,89 +1073,27 @@ class view_serializer
             m_out.put("null");
             return;
         }
-        write_float(x, std::integral_constant<bool, ::nlohmann::detail::has_native_float_format<number_float_t>::value>());
+        static constexpr bool is_ieee_single_or_double
+            = std::numeric_limits<number_float_t>::is_iec559
+              && ((std::numeric_limits<number_float_t>::digits == 24 && std::numeric_limits<number_float_t>::max_exponent == 128)
+                  || (std::numeric_limits<number_float_t>::digits == 53 && std::numeric_limits<number_float_t>::max_exponent == 1024));
+        write_float(x, std::integral_constant<bool, is_ieee_single_or_double>());
     }
 
-    void write_float(number_float_t x, std::true_type /*has_native_float_format*/)
+    void write_float(number_float_t x, std::true_type /*is_ieee_single_or_double*/)
     {
         std::array<char, 64> buf{};
         const char* const end = ::nlohmann::detail::to_chars(buf.data(), buf.data() + buf.size(), x);
         m_out.put(buf.data(), static_cast<std::size_t>(end - buf.data()));
     }
 
-    void write_float(number_float_t x, std::false_type /*has_native_float_format*/)
+    void write_float(number_float_t x, std::false_type /*is_ieee_single_or_double*/)
     {
         // other types (e.g. long double) are rare: the library writes them
         const string_t s = BasicJsonType(x).dump();
         m_out.put(s.data(), s.size());
     }
 
-    void write_string(const node& n)
-    {
-        const char* const s = m_doc.str(n);
-        m_out.put('"');
-        if ((n.flags & node_flags::storage) == 0 && (!m_style.ensure_ascii || is_ascii_without_delete(s, n.len)))
-        {
-            // a string of the source without escape sequences has nothing to
-            // escape (with ensure_ascii, if it is printable ASCII)
-            m_out.put(s, n.len);
-        }
-        else if (m_style.ensure_ascii)
-        {
-            write_escaped<true>(reinterpret_cast<const unsigned char*>(s), n.len); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-        }
-        else
-        {
-            write_escaped<false>(reinterpret_cast<const unsigned char*>(s), n.len); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-        }
-        m_out.put('"');
-    }
-
-    /// as serializer::dump_escaped(); strings of a document are valid UTF-8,
-    /// except in a damaged image loaded with image_check::bounds, for which
-    /// this throws what basic_json::dump() throws for the string
-    template<bool EnsureAscii>
-    void write_escaped(const unsigned char* s, std::size_t n)
-    {
-        std::size_t i = 0;
-        while (i < n)
-        {
-            std::size_t run = 0;
-            if (!EnsureAscii)
-            {
-                run = string_bulk_run(s + i, n - i);
-            }
-            else if (is_ascii_copyable(s[i]))
-            {
-                run = find_ascii_copyable_run(s + i, n - i);
-            }
-            if (run != 0)
-            {
-                m_out.put(reinterpret_cast<const char*>(s + i), run); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-                i += run;
-                continue;
-            }
-            std::uint32_t codepoint = s[i];
-            std::size_t len = 1;
-            if (codepoint >= 0x80)
-            {
-                len = validate_one_utf8(s + i, n - i);
-                if (NLOHMANN_VIEW_UNLIKELY(len == 0))
-                {
-                    invalid_utf8(s, n);
-                    return;
-                }
-                codepoint &= 0xFFu >> (len + 1);
-                for (std::size_t k = 1; k < len; ++k)
-                {
-                    codepoint = (codepoint << 6u) | (s[i + k] & 0x3Fu);
-                }
-            }
-            write_codepoint<EnsureAscii>(codepoint, s + i, len);
-            i += len;
-        }
-    }
-
     /// throw what basic_json::dump() throws for a string that is not valid UTF-8
     NLOHMANN_VIEW_NOINLINE static void invalid_utf8(const unsigned char* s, std::size_t n)
     {
@@ -1027,8 +1148,8 @@ class view_serializer
 
     void write_u_escape(std::uint32_t u)
     {
-        std::array<char, 6> e = {{'\\', 'u', 0, 0, 0, 0}};
-        hex4_lower(static_cast<std::uint16_t>(u), &e[2]);
+        static constexpr const char* hex = "0123456789abcdef";
+        const std::array<char, 6> e = {{'\\', 'u', hex[(u >> 12u) & 0xFu], hex[(u >> 8u) & 0xFu], hex[(u >> 4u) & 0xFu], hex[u & 0xFu]}};
         m_out.put(e.data(), e.size());
     }
 

include/nlohmann/detail/view/simd.hpp

@@ -116,6 +116,34 @@ NLOHMANN_VIEW_ALWAYS_INLINE const unsigned char* vector_plain_run(const unsigned
     }
     return p;
 }
+
+/*!
+@brief copy 16 bytes from p to w, and find the first quote, backslash,
+control character, or non-ASCII byte among them
+
+The bytes are copied whether or not they are all plain (the caller has room
+for 16 bytes and keeps only the plain ones).
+
+@return the offset of that byte, or 16 if there is none
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE unsigned copy_plain_run16(const unsigned char* p, char* w) noexcept
+{
+#if NLOHMANN_VIEW_NEON
+    const uint8x16_t in = vld1q_u8(p);
+    vst1q_u8(reinterpret_cast<std::uint8_t*>(w), in); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    const uint8x16_t special = vorrq_u8(vorrq_u8(vceqq_u8(in, vdupq_n_u8('"')), vceqq_u8(in, vdupq_n_u8('\\'))),
+                                        vcltq_s8(vreinterpretq_s8_u8(in), vdupq_n_s8(0x20)));
+    const std::uint64_t bits = vget_lane_u64(vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(special), 4)), 0);
+    return bits != 0 ? static_cast<unsigned>(count_trailing_zeros(bits) >> 2u) : 16u;
+#else
+    const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
+    _mm_storeu_si128(static_cast<__m128i*>(static_cast<void*>(w)), in); // NOLINT(bugprone-casting-through-void)
+    const __m128i special = _mm_or_si128(_mm_or_si128(_mm_cmpeq_epi8(in, _mm_set1_epi8('"')), _mm_cmpeq_epi8(in, _mm_set1_epi8('\\'))),
+                                         _mm_cmplt_epi8(in, _mm_set1_epi8(0x20)));
+    const auto bits = static_cast<std::uint64_t>(static_cast<unsigned>(_mm_movemask_epi8(special)));
+    return bits != 0 ? static_cast<unsigned>(count_trailing_zeros(bits)) : 16u;
+#endif
+}
 #endif
 
 #if NLOHMANN_VIEW_SSSE3_DISPATCH

include/nlohmann/detail/view/value.hpp

@@ -60,7 +60,7 @@ NLOHMANN_VIEW_ALWAYS_INLINE T arithmetic_value(const document_data& d, const nod
         case value_t::binary:
         case value_t::discarded:
         default:
-            throw_type_error(exception_id::type_mismatch, "type must be number, but is ", value_type_name(static_cast<value_t>(n.kind)));
+            throw_type_error(302, "type must be number, but is ", value_type_name(static_cast<value_t>(n.kind)));
     }
 }
 
@@ -70,7 +70,7 @@ std::vector<U, A> vector_value(const View& v)
 {
     if (NLOHMANN_VIEW_UNLIKELY(!v.is_array()))
     {
-        throw_type_error(exception_id::type_mismatch, "type must be array, but is ", v.type_name());
+        throw_type_error(302, "type must be array, but is ", v.type_name());
     }
     std::vector<U, A> r;
     r.reserve(v.size());
@@ -88,7 +88,7 @@ Map map_value(const View& v)
 {
     if (NLOHMANN_VIEW_UNLIKELY(!v.is_object()))
     {
-        throw_type_error(exception_id::type_mismatch, "type must be object, but is ", v.type_name());
+        throw_type_error(302, "type must be object, but is ", v.type_name());
     }
     Map r;
     for (auto it = v.begin(); it != v.end(); ++it)

include/nlohmann/json.hpp

@@ -55,7 +55,7 @@
 #include <nlohmann/detail/abi_macros.hpp> // IWYU pragma: export
 #include <nlohmann/detail/conversions/from_json.hpp> // IWYU pragma: keep
 #include <nlohmann/detail/conversions/to_json.hpp> // IWYU pragma: keep
-#include <nlohmann/detail/exceptions.hpp> // IWYU pragma: export
+#include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/hash.hpp>
 #include <nlohmann/detail/input/binary_reader.hpp>
 #include <nlohmann/detail/input/input_adapters.hpp>
@@ -159,9 +159,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     friend class ::nlohmann::detail::binary_writer;
     template<typename BasicJsonType, typename InputType, typename SAX>
     friend class ::nlohmann::detail::binary_reader;
-    template<typename BasicJsonType, typename InputAdapterType>
+    template<typename BasicJsonType, typename InputAdapterType, bool Collect>
     friend class ::nlohmann::detail::json_sax_dom_parser;
     template<typename BasicJsonType, typename InputAdapterType>
+    friend class ::nlohmann::detail::json_sax_dom_binary_parser;
+    template<typename BasicJsonType, typename InputAdapterType>
     friend class ::nlohmann::detail::json_sax_dom_callback_parser;
 #if JSON_DIAGNOSTIC_POSITIONS
     friend struct ::nlohmann::detail::diagnostic_positions;
@@ -374,9 +376,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         result["name"] = "JSON for Modern C++";
         result["url"] = "https://github.com/nlohmann/json";
         result["version"]["string"] =
-            detail::concat<string_t>(detail::to_string<string_t>(static_cast<std::size_t>(NLOHMANN_JSON_VERSION_MAJOR)), '.',
-                                     detail::to_string<string_t>(static_cast<std::size_t>(NLOHMANN_JSON_VERSION_MINOR)), '.',
-                                     detail::to_string<string_t>(static_cast<std::size_t>(NLOHMANN_JSON_VERSION_PATCH)));
+            detail::concat(std::to_string(NLOHMANN_JSON_VERSION_MAJOR), '.',
+                           std::to_string(NLOHMANN_JSON_VERSION_MINOR), '.',
+                           std::to_string(NLOHMANN_JSON_VERSION_PATCH));
         result["version"]["major"] = NLOHMANN_JSON_VERSION_MAJOR;
         result["version"]["minor"] = NLOHMANN_JSON_VERSION_MINOR;
         result["version"]["patch"] = NLOHMANN_JSON_VERSION_PATCH;
@@ -398,10 +400,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #elif defined(__clang__)
         result["compiler"] = {{"family", "clang"}, {"version", __clang_version__}};
 #elif defined(__GNUC__) || defined(__GNUG__)
-        result["compiler"] = {{"family", "gcc"}, {"version", detail::concat<string_t>(
-                    detail::to_string<string_t>(static_cast<std::size_t>(__GNUC__)), '.',
-                    detail::to_string<string_t>(static_cast<std::size_t>(__GNUC_MINOR__)), '.',
-                    detail::to_string<string_t>(static_cast<std::size_t>(__GNUC_PATCHLEVEL__)))
+        result["compiler"] = {{"family", "gcc"}, {"version", detail::concat(
+                    std::to_string(__GNUC__), '.',
+                    std::to_string(__GNUC_MINOR__), '.',
+                    std::to_string(__GNUC_PATCHLEVEL__))
             }
         };
 #elif defined(__HP_aCC)
@@ -419,9 +421,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #endif
 
 #if defined(_MSVC_LANG)
-        result["compiler"]["c++"] = detail::to_string<string_t>(static_cast<std::size_t>(_MSVC_LANG));
+        result["compiler"]["c++"] = std::to_string(_MSVC_LANG);
 #elif defined(__cplusplus)
-        result["compiler"]["c++"] = detail::to_string<string_t>(static_cast<std::size_t>(__cplusplus));
+        result["compiler"]["c++"] = std::to_string(__cplusplus);
 #else
         result["compiler"]["c++"] = "unknown";
 #endif
@@ -732,16 +734,24 @@ private:
         // true if v is not an array/object, or is an already-empty one
         static bool has_no_children(const basic_json& v) noexcept
         {
-            if (v.m_data.m_type == value_t::array)
+            switch (v.m_data.m_type)
             {
+                case value_t::array:
                     return v.m_data.m_value.array->empty();
-            }
-            if (v.m_data.m_type == value_t::object)
-            {
+                case value_t::object:
                     return v.m_data.m_value.object->empty();
-            }
+                case value_t::null:
+                case value_t::string:
+                case value_t::boolean:
+                case value_t::number_integer:
+                case value_t::number_unsigned:
+                case value_t::number_float:
+                case value_t::binary:
+                case value_t::discarded:
+                default:
                     return true;
             }
+        }
 
         // true if no child of the non-empty array/object v has children of
         // its own, i.e. v can be freed in one go (its destructor then
@@ -845,17 +855,28 @@ private:
         }
 
 public:
-        template<typename T>
-        static void destroy_pointer(T*& ptr) noexcept
+        void destroy_string() noexcept
         {
-            if (ptr == nullptr)
+            if (string == nullptr)
             {
                 // not initialized (e.g., due to exception in the ctor)
                 return;
             }
-            AllocatorType<T> alloc;
-            std::allocator_traits<decltype(alloc)>::destroy(alloc, ptr);
-            std::allocator_traits<decltype(alloc)>::deallocate(alloc, ptr, 1);
+            AllocatorType<string_t> alloc;
+            std::allocator_traits<decltype(alloc)>::destroy(alloc, string);
+            std::allocator_traits<decltype(alloc)>::deallocate(alloc, string, 1);
+        }
+
+        void destroy_binary() noexcept
+        {
+            if (binary == nullptr)
+            {
+                // not initialized (e.g., due to exception in the ctor)
+                return;
+            }
+            AllocatorType<binary_t> alloc;
+            std::allocator_traits<decltype(alloc)>::destroy(alloc, binary);
+            std::allocator_traits<decltype(alloc)>::deallocate(alloc, binary, 1);
         }
 
         // t must be value_t::array or value_t::object
@@ -1021,11 +1042,11 @@ public:
             switch (t)
             {
                 case value_t::string:
-                    destroy_pointer(string);
+                    destroy_string();
                     break;
 
                 case value_t::binary:
-                    destroy_pointer(binary);
+                    destroy_binary();
                     break;
 
                 case value_t::object:
@@ -1087,19 +1108,36 @@ public:
     void set_parents()
     {
 #if JSON_DIAGNOSTICS
-        if (m_data.m_type == value_t::array)
+        switch (m_data.m_type)
+        {
+            case value_t::array:
             {
                 for (auto& element : *m_data.m_value.array)
                 {
                     element.m_parent = this;
                 }
+                break;
             }
-        else if (m_data.m_type == value_t::object)
+
+            case value_t::object:
             {
                 for (auto& element : *m_data.m_value.object)
                 {
                     element.second.m_parent = this;
                 }
+                break;
+            }
+
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
+                break;
         }
 #endif
     }
@@ -2547,7 +2585,8 @@ public:
             case value_t::string:
             case value_t::binary:
             {
-                if (JSON_HEDLEY_UNLIKELY(!primitive_range_is_complete(first, last)))
+                if (JSON_HEDLEY_UNLIKELY(!first.m_it.primitive_iterator.is_begin()
+                                         || !last.m_it.primitive_iterator.is_end()))
                 {
                     detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_range_out_of_range, "iterators out of range", first.m_object);
                 }
@@ -3021,134 +3060,6 @@ public:
         JSON_THROW(std::length_error(detail::concat("array index ", std::to_string(idx), " exceeds size_type")));
     }
 
-    /// @throw type_error.309 always, as insert() is not defined for the type of @a j
-    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE
-    static void throw_insert_wrong_type(const basic_json& j)
-    {
-        detail::throw_cannot_use_with(detail::exception_id::insert_wrong_type, "insert()", j);
-    }
-
-    /// @throw invalid_iterator.202 always, as an iterator belongs to another value than @a obj
-    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE
-    static void throw_iterator_from_other_value(const basic_json* obj)
-    {
-        detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterator does not fit current value", obj);
-    }
-
-    /// @throw type_error.310 always, as swap() with the given operand is not defined for the type of @a j
-    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE
-    static void throw_swap_wrong_type(const char* operation, const basic_json& j)
-    {
-        detail::throw_cannot_use_with(detail::exception_id::swap_wrong_type, operation, j);
-    }
-
-    /// exchange the stored @a Stored value (if the value has that type) with @a other
-    template<typename Stored, typename Other>
-    void swap_impl(Other& other, const char* operation)
-    {
-        Stored* const stored = get_impl_ptr(static_cast<Stored*>(nullptr));
-        if (JSON_HEDLEY_UNLIKELY(stored == nullptr))
-        {
-            throw_swap_wrong_type(operation, *this);
-        }
-
-        using std::swap;
-        swap(*stored, other);
-    }
-
-    /// whether [first, last) spans the whole of a primitive value
-    template<typename IteratorType>
-    JSON_HEDLEY_ALWAYS_INLINE
-    static bool primitive_range_is_complete(const IteratorType& first, const IteratorType& last) noexcept
-    {
-        return first.m_it.primitive_iterator.is_begin() && last.m_it.primitive_iterator.is_end();
-    }
-
-    /// destroy the current (primitive) value and become null
-    void reset_to_null_impl()
-    {
-        m_data.m_value.destroy(m_data.m_type);
-        m_data.m_value = {};
-        m_data.m_type = value_t::null;
-        assert_invariant();
-    }
-
-    /// append @a val (moved or copied) to the array; a null value becomes an array
-    template<typename ValueType>
-    JSON_HEDLEY_ALWAYS_INLINE
-    void push_back_array_impl(ValueType&& val)
-    {
-        // push_back only works for null objects or arrays
-        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
-        {
-            detail::throw_cannot_use_with(detail::exception_id::push_back_wrong_type, "push_back()", *this);
-        }
-
-        // transform a null object into an array
-        if (is_null())
-        {
-            convert_null_to<array_t>();
-        }
-
-        // add the element to the array
-        const auto old_capacity = container_capacity();
-        m_data.m_value.array->push_back(std::forward<ValueType>(val));
-        set_parent_after_insert(m_data.m_value.array->back(), old_capacity);
-    }
-
-    /// parse the input behind an already created adapter
-    template<typename InputAdapterType>
-    static basic_json parse_impl(InputAdapterType&& adapter,
-                                 parser_callback_t cb,
-                                 const bool allow_exceptions,
-                                 const bool ignore_comments,
-                                 const bool ignore_trailing_commas)
-    {
-        basic_json result;
-        parser(std::forward<InputAdapterType>(adapter), std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas).parse(true, result);
-        return result;
-    }
-
-    /// check the input behind an already created adapter
-    template<typename InputAdapterType>
-    static bool accept_impl(InputAdapterType&& adapter,
-                            const bool ignore_comments,
-                            const bool ignore_trailing_commas)
-    {
-        return parser(std::forward<InputAdapterType>(adapter), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
-    }
-
-    /// generate SAX events from the input behind an already created adapter
-    template<typename InputAdapterType, typename SAX>
-    static bool sax_parse_impl(InputAdapterType ia, SAX* sax,
-                               const input_format_t format,
-                               const bool strict,
-                               const bool ignore_comments,
-                               const bool ignore_trailing_commas,
-                               const cbor_tag_handler_t tag_handler)
-    {
-        if (format == input_format_t::json)
-        {
-            return parser(std::move(ia), nullptr, true, ignore_comments, ignore_trailing_commas).sax_parse(sax, strict);
-        }
-        return detail::binary_reader<basic_json, InputAdapterType, SAX>(std::move(ia), format).sax_parse(sax, strict, tag_handler);
-    }
-
-    /// serialize @a j into a new vector; @a write receives the vector-backed writer
-    template<typename WriteFunction>
-    static std::vector<std::uint8_t> to_binary_vector(const basic_json& j, const error_handler_t error_handler, WriteFunction write)
-    {
-        std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_initial_capacity(j));
-        {
-            // the sink sets the size of result when it is destroyed, which
-            // must happen before result is returned (without NRVO, it is moved)
-            auto writer = vector_writer(result, error_handler);
-            write(writer);
-        }
-        return result;
-    }
-
     /// @throw out_of_range.401 always, as @a idx is out of range of @a j
     JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE
     static void throw_array_index_out_of_range(size_type idx, const basic_json& j)
@@ -4131,7 +4042,7 @@ public:
         // make sure the iterator fits the current value
         if (JSON_HEDLEY_UNLIKELY(this != pos.m_object))
         {
-            throw_iterator_from_other_value(this);
+            detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterator does not fit current value", this);
         }
 
         IteratorType result = end();
@@ -4150,7 +4061,10 @@ public:
                     detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_out_of_range, "iterator out of range", this);
                 }
 
-                reset_to_null_impl();
+                m_data.m_value.destroy(m_data.m_type);
+                m_data.m_value = {};
+                m_data.m_type = value_t::null;
+                assert_invariant();
                 break;
             }
 
@@ -4200,12 +4114,16 @@ public:
             case value_t::string:
             case value_t::binary:
             {
-                if (JSON_HEDLEY_UNLIKELY(!primitive_range_is_complete(first, last)))
+                if (JSON_HEDLEY_UNLIKELY(!first.m_it.primitive_iterator.is_begin()
+                                         || !last.m_it.primitive_iterator.is_end()))
                 {
                     detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_range_out_of_range, "iterators out of range", this);
                 }
 
-                reset_to_null_impl();
+                m_data.m_value.destroy(m_data.m_type);
+                m_data.m_value = {};
+                m_data.m_type = value_t::null;
+                assert_invariant();
                 break;
             }
 
@@ -4686,21 +4604,35 @@ public:
     JSON_HEDLEY_WARN_UNUSED_RESULT
     size_type max_size() const noexcept
     {
-        if (m_data.m_type == value_t::array)
+        switch (m_data.m_type)
+        {
+            case value_t::array:
             {
                 // delegate call to array_t::max_size()
                 return m_data.m_value.array->max_size();
             }
 
-        if (m_data.m_type == value_t::object)
+            case value_t::object:
             {
                 // delegate call to object_t::max_size()
                 return m_data.m_value.object->max_size();
             }
 
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
+            {
                 // all other types have max_size() == size()
                 return size();
             }
+        }
+    }
 
     /// @}
 
@@ -4777,7 +4709,22 @@ public:
     /// @sa https://json.nlohmann.me/api/basic_json/push_back/
     void push_back(basic_json&& val)
     {
-        push_back_array_impl(std::move(val));
+        // push_back only works for null objects or arrays
+        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
+        {
+            detail::throw_cannot_use_with(detail::exception_id::push_back_wrong_type, "push_back()", *this);
+        }
+
+        // transform a null object into an array
+        if (is_null())
+        {
+            convert_null_to<array_t>();
+        }
+
+        // add the element to the array (move semantics)
+        const auto old_capacity = container_capacity();
+        m_data.m_value.array->push_back(std::move(val));
+        set_parent_after_insert(m_data.m_value.array->back(), old_capacity);
         // if val is moved from, basic_json move constructor marks it null, so we do not call the destructor
     }
 
@@ -4793,7 +4740,22 @@ public:
     /// @sa https://json.nlohmann.me/api/basic_json/push_back/
     void push_back(const basic_json& val)
     {
-        push_back_array_impl(val);
+        // push_back only works for null objects or arrays
+        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
+        {
+            detail::throw_cannot_use_with(detail::exception_id::push_back_wrong_type, "push_back()", *this);
+        }
+
+        // transform a null object into an array
+        if (is_null())
+        {
+            convert_null_to<array_t>();
+        }
+
+        // add the element to the array
+        const auto old_capacity = container_capacity();
+        m_data.m_value.array->push_back(val);
+        set_parent_after_insert(m_data.m_value.array->back(), old_capacity);
     }
 
     /// @brief add an object to an array
@@ -4939,13 +4901,13 @@ public:
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
         {
-            throw_insert_wrong_type(*this);
+            detail::throw_cannot_use_with(detail::exception_id::insert_wrong_type, "insert()", *this);
         }
 
         // check if iterator pos fits to this JSON value
         if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
         {
-            throw_iterator_from_other_value(this);
+            detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterator does not fit current value", this);
         }
 
         // insert to array and return iterator
@@ -4959,13 +4921,13 @@ public:
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
         {
-            throw_insert_wrong_type(*this);
+            detail::throw_cannot_use_with(detail::exception_id::insert_wrong_type, "insert()", *this);
         }
 
         // check if iterator pos fits to this JSON value
         if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
         {
-            throw_iterator_from_other_value(this);
+            detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterator does not fit current value", this);
         }
 
         // moving into a local first keeps this safe even if val aliases
@@ -4981,13 +4943,13 @@ public:
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
         {
-            throw_insert_wrong_type(*this);
+            detail::throw_cannot_use_with(detail::exception_id::insert_wrong_type, "insert()", *this);
         }
 
         // check if iterator pos fits to this JSON value
         if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
         {
-            throw_iterator_from_other_value(this);
+            detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterator does not fit current value", this);
         }
 
         // insert to array and return iterator
@@ -5001,13 +4963,13 @@ public:
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
         {
-            throw_insert_wrong_type(*this);
+            detail::throw_cannot_use_with(detail::exception_id::insert_wrong_type, "insert()", *this);
         }
 
         // check if iterator pos fits to this JSON value
         if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
         {
-            throw_iterator_from_other_value(this);
+            detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterator does not fit current value", this);
         }
 
         // check if range iterators belong to the same JSON object
@@ -5038,13 +5000,13 @@ public:
         // insert only works for arrays
         if (JSON_HEDLEY_UNLIKELY(!is_array()))
         {
-            throw_insert_wrong_type(*this);
+            detail::throw_cannot_use_with(detail::exception_id::insert_wrong_type, "insert()", *this);
         }
 
         // check if iterator pos fits to this JSON value
         if (JSON_HEDLEY_UNLIKELY(pos.m_object != this))
         {
-            throw_iterator_from_other_value(this);
+            detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterator does not fit current value", this);
         }
 
         // copy the values first: ilist may refer to elements of this array
@@ -5066,7 +5028,7 @@ public:
         // insert only works for objects
         if (JSON_HEDLEY_UNLIKELY(!is_object()))
         {
-            throw_insert_wrong_type(*this);
+            detail::throw_cannot_use_with(detail::exception_id::insert_wrong_type, "insert()", *this);
         }
 
         // check if range iterators belong to the same JSON object
@@ -5308,37 +5270,82 @@ public:
     /// @sa https://json.nlohmann.me/api/basic_json/swap/
     void swap(array_t& other) // NOLINT(bugprone-exception-escape,cppcoreguidelines-noexcept-swap,performance-noexcept-swap)
     {
-        swap_impl<array_t>(other, "swap(array_t&)");
+        // swap only works for arrays
+        if (JSON_HEDLEY_LIKELY(is_array()))
+        {
+            using std::swap;
+            swap(*(m_data.m_value.array), other);
             set_parents();
         }
+        else
+        {
+            detail::throw_cannot_use_with(detail::exception_id::swap_wrong_type, "swap(array_t&)", *this);
+        }
+    }
 
     /// @brief exchanges the values
     /// @sa https://json.nlohmann.me/api/basic_json/swap/
     void swap(object_t& other) // NOLINT(bugprone-exception-escape,cppcoreguidelines-noexcept-swap,performance-noexcept-swap)
     {
-        swap_impl<object_t>(other, "swap(object_t&)");
+        // swap only works for objects
+        if (JSON_HEDLEY_LIKELY(is_object()))
+        {
+            using std::swap;
+            swap(*(m_data.m_value.object), other);
             set_parents();
         }
+        else
+        {
+            detail::throw_cannot_use_with(detail::exception_id::swap_wrong_type, "swap(object_t&)", *this);
+        }
+    }
 
     /// @brief exchanges the values
     /// @sa https://json.nlohmann.me/api/basic_json/swap/
     void swap(string_t& other) // NOLINT(bugprone-exception-escape,cppcoreguidelines-noexcept-swap,performance-noexcept-swap)
     {
-        swap_impl<string_t>(other, "swap(string_t&)");
+        // swap only works for strings
+        if (JSON_HEDLEY_LIKELY(is_string()))
+        {
+            using std::swap;
+            swap(*(m_data.m_value.string), other);
+        }
+        else
+        {
+            detail::throw_cannot_use_with(detail::exception_id::swap_wrong_type, "swap(string_t&)", *this);
+        }
     }
 
     /// @brief exchanges the values
     /// @sa https://json.nlohmann.me/api/basic_json/swap/
     void swap(binary_t& other) // NOLINT(bugprone-exception-escape,cppcoreguidelines-noexcept-swap,performance-noexcept-swap)
     {
-        swap_impl<binary_t>(other, "swap(binary_t&)");
+        // swap only works for binary values
+        if (JSON_HEDLEY_LIKELY(is_binary()))
+        {
+            using std::swap;
+            swap(*(m_data.m_value.binary), other);
+        }
+        else
+        {
+            detail::throw_cannot_use_with(detail::exception_id::swap_wrong_type, "swap(binary_t&)", *this);
+        }
     }
 
     /// @brief exchanges the values
     /// @sa https://json.nlohmann.me/api/basic_json/swap/
     void swap(typename binary_t::container_type& other) // NOLINT(bugprone-exception-escape)
     {
-        swap_impl<binary_t>(other, "swap(binary_t::container_type&)");
+        // swap only works for binary values
+        if (JSON_HEDLEY_LIKELY(is_binary()))
+        {
+            using std::swap;
+            swap(*(m_data.m_value.binary), other);
+        }
+        else
+        {
+            detail::throw_cannot_use_with(detail::exception_id::swap_wrong_type, "swap(binary_t::container_type&)", *this);
+        }
     }
 
     /// @}
@@ -6019,7 +6026,10 @@ public:
                             const bool ignore_comments = false,
                             const bool ignore_trailing_commas = false)
     {
-        return parse_impl(detail::input_adapter(std::forward<InputType>(i)), std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
+        basic_json result;
+        auto p = parser(detail::input_adapter(std::forward<InputType>(i)), std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
+        p.parse(true, result);
+        return result;
     }
 
     /// @brief deserialize from a pair of character iterators (or an iterator+sentinel pair, C++20 ranges support)
@@ -6034,7 +6044,10 @@ public:
                             const bool ignore_comments = false,
                             const bool ignore_trailing_commas = false)
     {
-        return parse_impl(detail::input_adapter(std::move(first), std::move(last)), std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
+        basic_json result;
+        auto p = parser(detail::input_adapter(std::move(first), std::move(last)), std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
+        p.parse(true, result);
+        return result;
     }
 
     JSON_HEDLEY_WARN_UNUSED_RESULT
@@ -6048,7 +6061,10 @@ public:
         = delete;
 #else
     {
-        return parse_impl(i.get(), std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
+        basic_json result;
+        auto p = parser(i.get(), std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
+        p.parse(true, result);
+        return result;
     }
 #endif
 
@@ -6060,7 +6076,7 @@ public:
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
-        return accept_impl(detail::input_adapter(std::forward<InputType>(i)), ignore_comments, ignore_trailing_commas);
+        return parser(detail::input_adapter(std::forward<InputType>(i)), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
     }
 
     /// @brief check if the input is valid JSON (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -6072,7 +6088,7 @@ public:
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
-        return accept_impl(detail::input_adapter(std::move(first), std::move(last)), ignore_comments, ignore_trailing_commas);
+        return parser(detail::input_adapter(std::move(first), std::move(last)), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
     }
 
     JSON_HEDLEY_WARN_UNUSED_RESULT
@@ -6084,7 +6100,7 @@ public:
         = delete;
 #else
     {
-        return accept_impl(i.get(), ignore_comments, ignore_trailing_commas);
+        return parser(i.get(), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
     }
 #endif
 
@@ -6099,7 +6115,10 @@ public:
                           const bool ignore_trailing_commas = false,
                           const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
     {
-        return sax_parse_impl(detail::input_adapter(std::forward<InputType>(i)), sax, format, strict, ignore_comments, ignore_trailing_commas, tag_handler);
+        auto ia = detail::input_adapter(std::forward<InputType>(i));
+        return format == input_format_t::json
+               ? parser(std::move(ia), nullptr, true, ignore_comments, ignore_trailing_commas).sax_parse(sax, strict)
+               : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia), format).sax_parse(sax, strict, tag_handler);
     }
 
     /// @brief generate SAX events (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -6114,7 +6133,10 @@ public:
                           const bool ignore_trailing_commas = false,
                           const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
     {
-        return sax_parse_impl(detail::input_adapter(std::move(first), std::move(last)), sax, format, strict, ignore_comments, ignore_trailing_commas, tag_handler);
+        auto ia = detail::input_adapter(std::move(first), std::move(last));
+        return format == input_format_t::json
+               ? parser(std::move(ia), nullptr, true, ignore_comments, ignore_trailing_commas).sax_parse(sax, strict)
+               : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia), format).sax_parse(sax, strict, tag_handler);
     }
 
     /// @brief generate SAX events
@@ -6148,7 +6170,12 @@ public:
     = delete;
 #else
     {
-        return sax_parse_impl(i.get(), sax, format, strict, ignore_comments, ignore_trailing_commas, tag_handler);
+        auto ia = i.get();
+        return format == input_format_t::json
+               // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
+               ? parser(std::move(ia), nullptr, true, ignore_comments, ignore_trailing_commas).sax_parse(sax, strict)
+               // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
+               : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia), format).sax_parse(sax, strict, tag_handler);
     }
 #endif
 #if defined(__clang__)
@@ -6263,7 +6290,7 @@ public:
            from_ubjson/from_bjdata/from_bon8/from_bson overloads
 
     Building the @ref binary_reader as a named local, rather than as a
-    temporary that @ref detail::json_sax_dom_parser::parse is called on in
+    temporary that @ref detail::json_sax_dom_binary_parser::parse is called on in
     the same expression, avoids a false-positive cppcheck accessMoved
     warning in each of the 16 callers.
     */
@@ -6274,7 +6301,7 @@ public:
                                        const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
     {
         basic_json result;
-        detail::json_sax_dom_parser<basic_json, InputAdapterType> sdp(result, allow_exceptions);
+        detail::json_sax_dom_binary_parser<basic_json, InputAdapterType> sdp(result, allow_exceptions);
         binary_reader<InputAdapterType> reader(std::move(ia), format, error_handler);
         if (!reader.sax_parse(&sdp, strict, tag_handler))
         {
@@ -6296,10 +6323,10 @@ public:
     static std::vector<std::uint8_t> to_cbor(const basic_json& j,
             const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        return to_binary_vector(j, error_handler, [&](vector_binary_writer<std::uint8_t>& w)
-        {
-            w.write_cbor(j);
-        });
+        std::vector<std::uint8_t> result;
+        result.reserve(detail::binary_initial_capacity(j));
+        vector_writer(result, error_handler).write_cbor(j);
+        return result;
     }
 
     /// @brief create a CBOR serialization of a given JSON value
@@ -6327,10 +6354,10 @@ public:
     static std::vector<std::uint8_t> to_msgpack(const basic_json& j,
             const error_handler_t error_handler = error_handler_t::keep)
     {
-        return to_binary_vector(j, error_handler, [&](vector_binary_writer<std::uint8_t>& w)
-        {
-            w.write_msgpack(j);
-        });
+        std::vector<std::uint8_t> result;
+        result.reserve(detail::binary_initial_capacity(j));
+        vector_writer(result, error_handler).write_msgpack(j);
+        return result;
     }
 
     /// @brief create a MessagePack serialization of a given JSON value
@@ -6360,10 +6387,10 @@ public:
             const bool use_type = false,
             const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        return to_binary_vector(j, error_handler, [&](vector_binary_writer<std::uint8_t>& w)
-        {
-            w.write_ubjson(j, use_size, use_type);
-        });
+        std::vector<std::uint8_t> result;
+        result.reserve(detail::binary_initial_capacity(j));
+        vector_writer(result, error_handler).write_ubjson(j, use_size, use_type);
+        return result;
     }
 
     /// @brief create a UBJSON serialization of a given JSON value
@@ -6396,10 +6423,10 @@ public:
             const bjdata_version_t version = bjdata_version_t::draft2,
             const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        return to_binary_vector(j, error_handler, [&](vector_binary_writer<std::uint8_t>& w)
-        {
-            w.write_ubjson(j, use_size, use_type, true, true, version);
-        });
+        std::vector<std::uint8_t> result;
+        result.reserve(detail::binary_initial_capacity(j));
+        vector_writer(result, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
+        return result;
     }
 
     /// @brief create a BJData serialization of a given JSON value
@@ -6431,10 +6458,10 @@ public:
     static std::vector<std::uint8_t> to_bson(const basic_json& j,
             const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        return to_binary_vector(j, error_handler, [&](vector_binary_writer<std::uint8_t>& w)
-        {
-            w.write_bson(j);
-        });
+        std::vector<std::uint8_t> result;
+        result.reserve(detail::binary_initial_capacity(j));
+        vector_writer(result, error_handler).write_bson(j);
+        return result;
     }
 
     /// @brief create a BSON serialization of a given JSON value
@@ -6461,10 +6488,10 @@ public:
     /// @sa https://json.nlohmann.me/api/basic_json/to_bon8/
     static std::vector<std::uint8_t> to_bon8(const basic_json& j)
     {
-        return to_binary_vector(j, detail::binary_writer_default_error_handler(), [&](vector_binary_writer<std::uint8_t>& w)
-        {
-            w.write_bon8(j);
-        });
+        std::vector<std::uint8_t> result;
+        result.reserve(detail::binary_initial_capacity(j));
+        vector_writer(result).write_bon8(j);
+        return result;
     }
 
     /// @brief create a BON8 serialization of a given JSON value
@@ -7800,14 +7827,9 @@ public:
             return;
         }
 
-        if (detail::is_primitive(source.type()))
+        switch (source.type())
         {
-            // both primitive types: replace value
-            diff_replace(result, path, target);
-            return;
-        }
-
-        if (source.is_array())
+            case value_t::array:
             {
                 const std::size_t path_length = path.size();
 
@@ -7828,8 +7850,10 @@ public:
                 // We now reached the end of at least one array
                 // in a second pass, traverse the remaining elements
                 diff_array_tails(result, source, target, path, i);
+                break;
             }
-        else
+
+            case value_t::object:
             {
                 diff_target_values target_values;
                 std::vector<const_iterator> added;
@@ -7863,6 +7887,23 @@ public:
                     // append the "add" operations for brand-new keys
                     diff_added(result, added, path);
                 }
+                break;
+            }
+
+            case value_t::null:
+            case value_t::string:
+            case value_t::boolean:
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
+            {
+                // both primitive types: replace value
+                diff_replace(result, path, target);
+                break;
+            }
         }
     }
 
@@ -7907,19 +7948,15 @@ public:
                 return;
             }
 
-            if (detail::is_primitive(s.type()))
+            switch (s.type())
             {
-                // both primitive types: replace value
-                diff_replace(result, current_path, t);
-                return;
-            }
-
-            if (s.is_array())
+                case value_t::array:
                 {
                     stack.emplace_back(&s, &t, current_path.size());
                     return;
                 }
-            else
+
+                case value_t::object:
                 {
                     std::vector<const basic_json*> target_values;
                     std::vector<const_iterator> added;
@@ -7935,6 +7972,22 @@ public:
                     }
                     return;
                 }
+
+                case value_t::null:
+                case value_t::string:
+                case value_t::boolean:
+                case value_t::number_integer:
+                case value_t::number_unsigned:
+                case value_t::number_float:
+                case value_t::binary:
+                case value_t::discarded:
+                default:
+                {
+                    // both primitive types: replace value
+                    diff_replace(result, current_path, t);
+                    return;
+                }
+            }
         };
 
         enter(source, target);

include/nlohmann/json_view.hpp

@@ -30,6 +30,7 @@
 #include <array> // array
 #include <cstddef> // nullptr_t, size_t // IWYU pragma: keep
 #include <cstdint> // uint8_t, uint32_t
+#include <cstdio> // FILE
 #include <cstring> // memcpy, strlen
 #include <istream> // istream // IWYU pragma: keep
 #include <iterator> // distance, input_iterator_tag, iterator_traits
@@ -267,7 +268,7 @@ class basic_json_view
             {
                 return {};
             }
-            detail::view::throw_type_error(detail::exception_id::subscript_wrong_type, "cannot use operator[] with a string argument with ", type_name());
+            detail::view::throw_type_error(305, "cannot use operator[] with a string argument with ", type_name());
         }
         return lookup(key);
     }
@@ -293,9 +294,9 @@ class basic_json_view
             {
                 return {};
             }
-            detail::view::throw_type_error(detail::exception_id::subscript_wrong_type, "cannot use operator[] with a numeric argument with ", type_name());
+            detail::view::throw_type_error(305, "cannot use operator[] with a numeric argument with ", type_name());
         }
-        return idx < m_node->len ? basic_json_view(m_doc, navigation::value(detail::view::element_at<Editable>(*m_doc, m_node, idx))) : basic_json_view();
+        return idx < m_node->len ? element(idx) : basic_json_view();
     }
 
     /// any other integer type (int, unsigned, long, std::int64_t, ...; a
@@ -326,12 +327,12 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_object()))
         {
-            detail::view::throw_type_error(detail::exception_id::at_wrong_type, "cannot use at() with ", type_name());
+            detail::view::throw_type_error(304, "cannot use at() with ", type_name());
         }
         const basic_json_view r = lookup(key);
         if (NLOHMANN_VIEW_UNLIKELY(r.is_discarded()))
         {
-            detail::view::throw_key_not_found(std::string(key.data(), key.size()));
+            detail::view::throw_out_of_range(403, detail::concat("key '", std::string(key.data(), key.size()), "' not found"));
         }
         return r;
     }
@@ -352,13 +353,13 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_array()))
         {
-            detail::view::throw_type_error(detail::exception_id::at_wrong_type, "cannot use at() with ", type_name());
+            detail::view::throw_type_error(304, "cannot use at() with ", type_name());
         }
         if (NLOHMANN_VIEW_UNLIKELY(idx >= m_node->len))
         {
-            detail::view::throw_array_index_out_of_range(idx);
+            detail::view::throw_out_of_range(401, detail::concat("array index ", std::to_string(idx), " is out of range"));
         }
-        return basic_json_view(m_doc, navigation::value(detail::view::element_at<Editable>(*m_doc, m_node, idx)));
+        return element(idx);
     }
 
     /// any other integer type, see operator[]; negative values are out of
@@ -384,7 +385,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_object()))
         {
-            detail::view::throw_type_error(detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
+            detail::view::throw_type_error(306, "cannot use value() with ", type_name());
         }
         const basic_json_view r = lookup(key);
         return r.is_discarded() ? default_value : r.template get<T>();
@@ -392,7 +393,13 @@ class basic_json_view
 
     string_t value(string_view_t key, const char* default_value) const
     {
-        return value(key, string_t(default_value));
+        if (NLOHMANN_VIEW_UNLIKELY(!is_object()))
+        {
+            detail::view::throw_type_error(306, "cannot use value() with ", type_name());
+        }
+        // (the default is made only if there is no such member)
+        const basic_json_view r = lookup(key);
+        return r.is_discarded() ? string_t(default_value) : r.template get<string_t>();
     }
 
     /// the value a JSON pointer refers to converted to T, or the default
@@ -403,7 +410,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_structured()))
         {
-            detail::view::throw_type_error(detail::exception_id::value_wrong_type, "cannot use value() with ", type_name());
+            detail::view::throw_type_error(306, "cannot use value() with ", type_name());
         }
         const basic_json_view r = detail::view::resolve_pointer(*this, detail::json_pointer_access::reference_tokens(ptr), detail::view::pointer_mode::value);
         return r.is_discarded() ? default_value : r.template get<T>();
@@ -411,7 +418,12 @@ class basic_json_view
 
     string_t value(const json_pointer& ptr, const char* default_value) const
     {
-        return value(ptr, string_t(default_value));
+        if (NLOHMANN_VIEW_UNLIKELY(!is_structured()))
+        {
+            detail::view::throw_type_error(306, "cannot use value() with ", type_name());
+        }
+        const basic_json_view r = detail::view::resolve_pointer(*this, detail::json_pointer_access::reference_tokens(ptr), detail::view::pointer_mode::value);
+        return r.is_discarded() ? string_t(default_value) : r.template get<string_t>();
     }
 
     /// the first element or member value; a primitive value itself. Throws
@@ -421,7 +433,7 @@ class basic_json_view
         const iterator it = begin();
         if (NLOHMANN_VIEW_UNLIKELY(it == end()))
         {
-            detail::view::throw_invalid_iterator(detail::exception_id::iterator_value_unavailable, "cannot get value");
+            detail::view::throw_invalid_iterator(214, "cannot get value");
         }
         return *it;
     }
@@ -433,7 +445,8 @@ class basic_json_view
     {
         if (is_structured() && m_node->len != 0)
         {
-            return basic_json_view(m_doc, navigation::value(detail::view::last_child<Editable>(*m_doc, m_node) + (is_object() ? 1 : 0)));
+            return unedited() ? basic_json_view(m_doc, detail::view::last_child<false>(*m_doc, m_node) + (is_object() ? 1 : 0))
+                   : basic_json_view(m_doc, navigation::value(detail::view::last_child<Editable>(*m_doc, m_node) + (is_object() ? 1 : 0)));
         }
         return front();
     }
@@ -450,7 +463,7 @@ class basic_json_view
         {
             return end();
         }
-        const node* const k = detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size());
+        const node* const k = find_key(key);
         return k != nullptr ? iterator(m_doc, k, true) : end();
     }
 
@@ -467,7 +480,7 @@ class basic_json_view
     /// whether this is an object with a member with this key
     bool contains(string_view_t key) const
     {
-        return is_object() && detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size()) != nullptr;
+        return is_object() && find_key(key) != nullptr;
     }
 
     bool contains(const char* key) const
@@ -573,7 +586,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_string()))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be string, but is ", type_name());
+            detail::view::throw_type_error(302, "type must be string, but is ", type_name());
         }
         return {m_doc->str(*m_node), m_node->len};
     }
@@ -585,7 +598,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_number()))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be number, but is ", type_name());
+            detail::view::throw_type_error(302, "type must be number, but is ", type_name());
         }
         return {m_doc->str(*m_node), detail::view::number_length(*m_node)};
     }
@@ -627,7 +640,14 @@ class basic_json_view
         // the compact writer keeps 64 bytes of slack, so that it does not grow
         // the buffer just before the end
         const std::size_t estimate = source_extent() + (style.pretty ? source_extent() / 2 : 0) + 160;
+        if (unedited())
+        {
+            detail::view::view_serializer<BasicJsonType, false>(*m_doc, out, estimate, style).dump(m_node);
+        }
+        else
+        {
             detail::view::view_serializer<BasicJsonType, Editable>(*m_doc, out, estimate, style).dump(m_node);
+        }
         return out;
     }
 
@@ -707,7 +727,7 @@ class basic_json_view
         {
             return BasicJsonType(value_t::discarded);
         }
-        return detail::view::materialize<BasicJsonType, Editable>(*m_doc, m_node);
+        return unedited() ? detail::view::materialize<BasicJsonType, false>(*m_doc, m_node) : detail::view::materialize<BasicJsonType, Editable>(*m_doc, m_node);
     }
 
     /// byte offset of this value in the source text (for strings: of the
@@ -785,17 +805,57 @@ class basic_json_view
     /// (object required)
     NLOHMANN_VIEW_ALWAYS_INLINE basic_json_view lookup(string_view_t key) const noexcept
     {
+        if (unedited())
+        {
+            const node* const k = detail::view::find_member<false>(*m_doc, m_node, key.data(), key.size());
+            return k != nullptr ? basic_json_view(m_doc, k + 1) : basic_json_view();
+        }
         const node* const k = detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size());
         return k != nullptr ? basic_json_view(m_doc, navigation::value(k + 1)) : basic_json_view();
     }
 
+    /// whether the document has not been edited yet: until the first edit, its index is walked like that of a
+    /// read-only document (nothing is moved or linked), which is cheaper
+    NLOHMANN_VIEW_ALWAYS_INLINE bool unedited() const noexcept
+    {
+        return !navigation::editable() || m_doc->edits == nullptr;
+    }
+
+    /// the member of this object with @a key (the last one if the key occurs more than once), or nullptr
+    NLOHMANN_VIEW_ALWAYS_INLINE const node* find_key(string_view_t key) const
+    {
+        return find_key(key, std::integral_constant<bool, Editable> {});
+    }
+
+    NLOHMANN_VIEW_ALWAYS_INLINE const node* find_key(string_view_t key, std::true_type /*editable*/) const
+    {
+        // (an editable document without edits is looked up as one that cannot be edited)
+        return unedited() ? detail::view::find_member<false>(*m_doc, m_node, key.data(), key.size())
+               : detail::view::find_member<true>(*m_doc, m_node, key.data(), key.size());
+    }
+
+    NLOHMANN_VIEW_ALWAYS_INLINE const node* find_key(string_view_t key, std::false_type /*editable*/) const
+    {
+        return detail::view::find_member<false>(*m_doc, m_node, key.data(), key.size());
+    }
+
+    /// the element of an array at an index below its size
+    NLOHMANN_VIEW_ALWAYS_INLINE basic_json_view element(size_type idx) const
+    {
+        if (unedited())
+        {
+            return basic_json_view(m_doc, detail::view::element_at<false>(*m_doc, m_node, idx));
+        }
+        return basic_json_view(m_doc, navigation::value(detail::view::element_at<Editable>(*m_doc, m_node, idx)));
+    }
+
     // --- get() dispatch ---
 
     bool get_impl(detail::view::value_tag<bool> /*unused*/, detail::priority_tag<2> /*unused*/) const
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_boolean()))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be boolean, but is ", type_name());
+            detail::view::throw_type_error(302, "type must be boolean, but is ", type_name());
         }
         return (m_node->flags & detail::view::node_flags::is_true) != 0;
     }
@@ -805,7 +865,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(m_node == nullptr))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be number, but is ", type_name());
+            detail::view::throw_type_error(302, "type must be number, but is ", type_name());
         }
         return detail::view::arithmetic_value<T, BasicJsonType>(*m_doc, *m_node);
     }
@@ -814,7 +874,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_null()))
         {
-            detail::view::throw_type_error(detail::exception_id::type_mismatch, "type must be null, but is ", type_name());
+            detail::view::throw_type_error(302, "type must be null, but is ", type_name());
         }
         return nullptr;
     }
@@ -1123,7 +1183,7 @@ class basic_json_document
     {
         if (NLOHMANN_VIEW_UNLIKELY(!m_data || m_data->discarded))
         {
-            detail::view::throw_type_error(detail::exception_id::document_image_unsupported, "cannot save a discarded json_document");
+            detail::view::throw_type_error(320, "cannot save a discarded json_document");
         }
         return detail::view::save_image(*m_data);
     }
@@ -1224,7 +1284,7 @@ class basic_json_document
                 const std::size_t idx = pointer_index(token);
                 if (idx >= 0xFFFFFFFFu)
                 {
-                    detail::view::throw_array_index_out_of_range(idx);
+                    detail::view::throw_out_of_range(401, detail::concat("array index ", std::to_string(idx), " is out of range"));
                 }
                 for (std::size_t i = 0; i < idx; ++i)
                 {
@@ -1280,7 +1340,7 @@ class basic_json_document
     {
         if (ptr.empty())
         {
-            detail::view::throw_out_of_range(detail::exception_id::patch_on_root, "JSON pointer has no parent");
+            detail::view::throw_out_of_range(405, "JSON pointer has no parent");
         }
         const view_type parent = root().at(ptr.parent_pointer());
         const auto& token = ptr.back();
@@ -1300,7 +1360,7 @@ class basic_json_document
         static_assert(Editable, "only an editable document can be edited: use basic_json_document<BasicJsonType, true> (json_editable_document)");
         if (NLOHMANN_VIEW_UNLIKELY(!m_data || m_data->discarded))
         {
-            detail::view::throw_invalid_iterator(detail::exception_id::iterator_from_other_value, "view does not belong to this document");
+            detail::view::throw_invalid_iterator(202, "view does not belong to this document");
         }
         return detail::view::editor<BasicJsonType, view_type>(*m_data);
     }
@@ -1317,7 +1377,7 @@ class basic_json_document
     {
         if (idx < 0)
         {
-            detail::view::throw_array_index_out_of_range(idx);
+            detail::view::throw_out_of_range(401, detail::concat("array index ", std::to_string(idx), " is out of range"));
         }
         return static_cast<std::size_t>(idx);
     }
@@ -1528,7 +1588,8 @@ class basic_json_document
         // NOLINTBEGIN(readability-avoid-nested-conditional-operator): a constant expression of C++11
         append_input_impl(buf, std::forward<T>(input), std::integral_constant < int, detail::is_contiguous_byte_container<D>::value ? 0
                           : std::is_base_of<std::istream, D>::value ? 1
-                          : detail::view::is_adapter_input<D>::value ? 2 : 3 > {});
+                          : detail::view::is_adapter_input<D>::value ? 2
+                          : detail::view::is_c_stream<D>::value ? 4 : 3 > {});
         // NOLINTEND(readability-avoid-nested-conditional-operator)
     }
 
@@ -1550,6 +1611,19 @@ class basic_json_document
         detail::view::append_adapter(buf, std::move(input.ia));
     }
 
+#ifndef JSON_NO_IO
+    static void append_input_impl(std::string& buf, std::FILE* file, std::integral_constant<int, 4> /*C stream*/)
+    {
+        if (file == nullptr)
+        {
+            // (as before: the library's adapter decides what a null stream yields)
+            detail::view::append_adapter(buf, detail::input_adapter(file));
+            return;
+        }
+        detail::view::append_file(buf, file);
+    }
+#endif
+
     template<typename T>
     static void append_input_impl(std::string& buf, T&& input, std::integral_constant<int, 3> /*other*/)
     {

include/nlohmann/ordered_map.hpp

@@ -125,19 +125,6 @@ private:
         Container::pop_back();
     }
 
-    /// @brief remove the entry with the given key; returns the number of removed entries
-    template<class K>
-    size_type erase_impl(const K& key)
-    {
-        const auto it = find_impl(*this, key);
-        if (it != this->end())
-        {
-            erase_at(it);
-            return 1;
-        }
-        return 0;
-    }
-
 public:
     template<class V, detail::enable_if_t<
                  detail::is_constructible<T, V>::value, int> = 0>
@@ -227,14 +214,26 @@ public:
 
     size_type erase(const key_type& key)
     {
-        return erase_impl(key);
+        const auto it = find_impl(*this, key);
+        if (it != this->end())
+        {
+            erase_at(it);
+            return 1;
+        }
+        return 0;
     }
 
     template<class KeyType, detail::enable_if_t<
                  detail::is_usable_as_key_type<key_compare, key_type, KeyType>::value, int> = 0>
     size_type erase(KeyType && key) // NOLINT(cppcoreguidelines-missing-std-forward)
     {
-        return erase_impl(key);
+        const auto it = find_impl(*this, key);
+        if (it != this->end())
+        {
+            erase_at(it);
+            return 1;
+        }
+        return 0;
     }
 
     iterator erase(iterator pos)

src/modules/json.cppm

@@ -60,6 +60,7 @@ inline namespace json_literals
 namespace detail
 {
     using NLOHMANN_JSON_NAMESPACE::detail::json_sax_dom_callback_parser;
+    using NLOHMANN_JSON_NAMESPACE::detail::json_sax_dom_parser;
     using NLOHMANN_JSON_NAMESPACE::detail::unknown_size;
 } // namespace detail
 

tests/src/unit-class_lexer.cpp

@@ -2042,118 +2042,3 @@ TEST_CASE("string scanning kernels")
     CHECK(nlohmann::detail::read_eight_bytes(bytes.data() + 8) == 0xFF0F0E0D0C0B0A09u);
     CHECK(nlohmann::detail::read_eight_bytes(reinterpret_cast<const char*>(bytes.data()) + 3) == 0x0B0A090807060504u);
 }
-
-TEST_CASE("find_ascii_copyable_run agrees with is_ascii_copyable for every byte")
-{
-    // the SWAR mask in find_ascii_copyable_run() encodes the predicate a
-    // second time; check every byte value at every position of a 24-byte buffer
-    // (three words) and for several lengths, with the byte at the end or inside
-    for (unsigned int value = 0; value < 256; ++value)
-    {
-        for (std::size_t position = 0; position < 24; ++position)
-        {
-            std::array<unsigned char, 24> buffer{};
-            buffer.fill(static_cast<unsigned char>('a'));
-            buffer[position] = static_cast<unsigned char>(value);
-            const bool copyable = nlohmann::detail::is_ascii_copyable(static_cast<unsigned char>(value));
-            for (const std::size_t n :
-                    {
-                        position, position + 1, std::size_t{24}
-                    })
-            {
-                if (n > 24)
-                {
-                    continue;
-                }
-                const std::size_t expected = (copyable || n <= position) ? n : position;
-                CAPTURE(value)
-                CAPTURE(position)
-                CAPTURE(n)
-                CHECK(nlohmann::detail::find_ascii_copyable_run(buffer.data(), n) == expected);
-            }
-        }
-    }
-}
-
-TEST_CASE("UTF-8 validators accept the same sequences")
-{
-    // The library checks UTF-8 in several places: detail::decode (serializer),
-    // the per-lead-byte switch of the lexer (json::accept), validate_one_utf8
-    // (bulk string scan), utf8_shape, and the byte path of the BON8 reader.
-    // They must accept exactly the same sequences (RFC 3629, section 4).
-    using nlohmann::json;
-
-    // bytes for the third and fourth position: the first two pairs are checked
-    // against all validators, the others only against the cheap ones
-    const std::array<std::array<unsigned char, 2>, 6> tails =
-    {
-        {
-            {{0x80, 0x80}}, {{0xBF, 0xBF}}, {{0x7F, 0x80}}, {{0xC0, 0x80}}, {{0x80, 0x7F}}, {{0x80, 0xC0}}
-        }
-    };
-
-    for (unsigned lead = 0x80; lead <= 0xFF; ++lead)
-    {
-        const auto shape = nlohmann::detail::utf8_shape(static_cast<std::uint8_t>(lead));
-        for (unsigned second = 0; second <= 0xFF; ++second)
-        {
-            for (std::size_t t = 0; t < tails.size(); ++t)
-            {
-                const std::array<unsigned char, 4> bytes = {{static_cast<unsigned char>(lead), static_cast<unsigned char>(second), tails[t][0], tails[t][1]}};
-
-                // expectation from the shape: the sequence is bytes[0..length)
-                const std::size_t length = shape.length;
-                bool expected = length >= 2 && second >= shape.second_lo && second <= shape.second_hi;
-                for (std::size_t i = 2; expected && i < length; ++i)
-                {
-                    expected = bytes[i] >= 0x80 && bytes[i] <= 0xBF;
-                }
-
-                // the DFA of the serializer
-                bool dfa = length >= 2;
-                if (dfa)
-                {
-                    std::uint8_t state = nlohmann::detail::UTF8_ACCEPT;
-                    std::uint32_t codep = 0;
-                    for (std::size_t i = 0; i < length; ++i)
-                    {
-                        nlohmann::detail::decode(state, codep, bytes[i]);
-                    }
-                    dfa = state == nlohmann::detail::UTF8_ACCEPT;
-                }
-
-                // the bulk path: exactly the sequence, and one byte short
-                const std::size_t bulk = nlohmann::detail::validate_one_utf8(bytes.data(), length);
-                const std::size_t bulk_short = length > 0 ? nlohmann::detail::validate_one_utf8(bytes.data(), length - 1) : 0;
-
-                CAPTURE(lead)
-                CAPTURE(second)
-                CAPTURE(t)
-                CHECK((dfa == expected && bulk == (expected ? length : 0) && bulk_short == 0));
-
-                if (t < 2 && length >= 2)
-                {
-                    // the lexer's byte path
-                    const std::string sequence(reinterpret_cast<const char*>(bytes.data()), length); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-                    CHECK(json::accept("\"" + sequence + "\"") == expected);
-
-                    // the byte path of the BON8 reader (a string ends at 0xFF)
-                    if (lead >= 0xC2 && lead <= 0xF7)
-                    {
-                        std::vector<std::uint8_t> packed(bytes.begin(), bytes.begin() + static_cast<std::ptrdiff_t>(length));
-                        packed.push_back(0xFF);
-                        const json j = json::from_bon8(packed, true, false);
-                        if (expected)
-                        {
-                            CHECK(j == json(sequence));
-                        }
-                        else
-                        {
-                            CHECK_FALSE((j.is_string() && j.get<std::string>() == sequence));
-                        }
-                    }
-                }
-            }
-        }
-    }
-}

tests/src/unit-class_parser.cpp

@@ -2952,3 +2952,81 @@ TEST_CASE("diagnostic positions: value lifetime, input adapters, and SAX")
     }
 }
 #endif
+
+TEST_CASE("accept() agrees with parse() on floats around the overflow limit")
+{
+    // accept() does not convert a float that cannot overflow; the tokens
+    // around the limit (and beyond it) must still be rejected exactly as
+    // parse() rejects them
+    const std::vector<const char*> numbers =
+    {
+        "1e0", "123.456e-5", "1e-400", "-1e-400", "1e307", "1e308", "1e309", "-1e309",
+        "10e307", "100e307", "0.1e309", "0.1e310", "1E+308", "1E+309",
+        "1.7976931348623157e308", "1.7976931348623159e308", "1.8e308", "-1.7976931348623157e308",
+        "12345678901234567e291", "12345678901234567e292", "123456789012345678e290", "123456789012345678e291",
+        "1234567890123456789e289", "1234567890123456789e290", "9999999999999999999e289", "9999999999999999999e290",
+        "0.00000000000000000001e328", "0.00000000000000000001e329"
+    };
+
+    for (const char* number : numbers)
+    {
+        for (const std::string& text :
+                {
+                    std::string(number), "[" + std::string(number) + "]", "{\"a\":" + std::string(number) + "}"
+                })
+        {
+            INFO(text);
+            const bool parses = !json::parse(text, nullptr, false).is_discarded();
+            CHECK(json::accept(text) == parses);
+        }
+    }
+}
+
+namespace
+{
+// a DOM parser that reports parse errors without throwing, as in the sax_no_exception example
+template<typename BasicJsonType>
+class quiet_dom_parser : public nlohmann::detail::json_sax_dom_parser<BasicJsonType, nlohmann::detail::string_input_adapter_type>
+{
+  public:
+    explicit quiet_dom_parser(BasicJsonType& j)
+        : nlohmann::detail::json_sax_dom_parser<BasicJsonType, nlohmann::detail::string_input_adapter_type>(j, false)
+    {}
+
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const nlohmann::detail::exception& /*unused*/)
+    {
+        return false;
+    }
+};
+
+template<typename BasicJsonType>
+std::string read_before_error(const std::string& text)
+{
+    BasicJsonType j;
+    quiet_dom_parser<BasicJsonType> sax(j);
+    CHECK(!BasicJsonType::sax_parse(text, &sax));
+    return j.dump();
+}
+} // namespace
+
+TEST_CASE("a json_sax_dom_parser keeps the values read before a parse error")
+{
+    // a json_sax_dom_parser that a user constructs stores every value in place, so a
+    // handler that does not throw on a parse error sees what was read before it
+    const std::vector<std::pair<std::string, std::string>> cases =
+    {
+        {"[1,2,3,]", "[1,2,3]"},
+        {"[[1,[2,3],4],[5,", "[[1,[2,3],4],[5]]"},
+        {R"({"a":1,"b":[1,2,{"c":)", R"({"a":1,"b":[1,2,{"c":null}]})"},
+        {R"({"a":1,"a":)", R"({"a":1})"},
+        {"[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,]", "[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]"},
+        {R"({"k0":0,"k1":1,"k2":{"x":[true,)", R"({"k0":0,"k1":1,"k2":{"x":[true]}})"},
+        {R"([{},[],{"a":[]},x)", R"([{},[],{"a":[]}])"},
+    };
+    for (const auto& c : cases)
+    {
+        CAPTURE(c.first)
+        CHECK(read_before_error<json>(c.first) == c.second);
+        CHECK(read_before_error<nlohmann::ordered_json>(c.first) == c.second);
+    }
+}

tests/src/unit-json_view.cpp

@@ -185,6 +185,33 @@ TEST_CASE("json_view")
         // duplicate keys: the last value, at the position of the first key
         CHECK(materialized<json_document>(R"({"a":1,"b":2,"a":3})") == json::parse(R"({"a":1,"b":2,"a":3})"));
         CHECK(materialized<ordered_json_document>(R"({"a":1,"b":2,"a":3})").dump() == R"({"a":3,"b":2})");
+        // scalars (made without the handler), and nesting around the depth up to which the stack of open containers is local
+        for (const char* scalar :
+                {"null", "true", "false", "0", "-7", "18446744073709551615", "1.5e300", "-0.0", "\"\"", "\"short\"", "\"a string that is longer than fifteen bytes\"", R"("\u00e4\n")"
+                })
+        {
+            CAPTURE(scalar)
+            CHECK(materialized<json_document>(scalar) == json::parse(scalar));
+            const std::string in_array = std::string("[1,") + scalar + "]";
+            const json_document d = json_document::parse(in_array);
+            CHECK(d.root()[1].materialize() == json::parse(scalar));
+            CHECK(d.root()[1].get<json>() == json::parse(scalar));
+        }
+        for (const std::size_t levels :
+                {
+                    std::size_t{1}, std::size_t{15}, std::size_t{16}, std::size_t{17}, std::size_t{32}, std::size_t{33}
+                })
+        {
+            CAPTURE(levels)
+            const std::string nested = std::string(levels, '[') + R"({"k":[1,{"j":2}]})" + std::string(levels, ']');
+            CHECK(materialized<json_document>(nested) == json::parse(nested));
+            std::string wide = R"({"a":)";
+            wide += nested;
+            wide += R"(,"b":)";
+            wide += nested;
+            wide += "}";
+            CHECK(materialized<json_document>(wide) == json::parse(wide));
+        }
         // very deep nesting (iterative, as parse())
         const std::string deep = std::string(100000, '[') + std::string(100000, ']');
         // (one check per step, so that a failure shows which step it is)
@@ -410,6 +437,31 @@ TEST_CASE("json_view")
         std::istringstream rvalue_source("[1]");
         CHECK(json_document::parse_copy(std::move(rvalue_source)).owns_source());
 
+        // a C stream is read in blocks as well (more than one block, and a
+        // text whose length is a multiple of the block size)
+        for (const std::size_t extra :
+                {
+                    std::size_t{0}, std::size_t{1}
+                })
+        {
+            std::FILE* long_file = std::tmpfile(); // NOLINT(cppcoreguidelines-owning-memory)
+            if (long_file != nullptr)
+            {
+                std::string padded = text;
+                padded.append(((4096 - (padded.size() % 4096)) % 4096) + extra, ' ');
+                CHECK(std::fwrite(padded.data(), 1, padded.size(), long_file) == padded.size());
+                CHECK(std::fseek(long_file, 0, SEEK_SET) == 0);
+                const json_document from_long_file = json_document::parse(long_file);
+                CHECK(from_long_file.source() == padded);
+                CHECK(from_long_file.root().materialize() == json::parse(text));
+                CHECK(std::fclose(long_file) == 0); // NOLINT(cppcoreguidelines-owning-memory)
+            }
+        }
+        {
+            json_document from_null;
+            CHECK_THROWS_AS(from_null = json_document::parse(static_cast<std::FILE*>(nullptr)), json::parse_error&);
+        }
+
         // a stream without a buffer is an empty input
         std::istream no_buffer(nullptr);
         CHECK(json_document::parse(no_buffer, false).is_discarded());
@@ -1006,6 +1058,49 @@ TEST_CASE("json_view element access and iteration")
 #endif
     }
 
+    SECTION("arrays whose elements have no subtrees: index and back()")
+    {
+        // (the elements are adjacent in the index; an array, an object, or an
+        // empty container anywhere makes the lookup skip element by element)
+        const std::vector<std::string> texts =
+        {
+            "[]", "[1]", "[1,2,3]", "[1,\"two\",3.5,true,null,-7,18446744073709551615]", "[[]]", "[{}]", "[1,[2],3]",
+            "[1,2,{\"a\":3}]", "[[1,2],3,4]", "[1,2,3,[4,5,6,7,8],9,10,11,12]", "[{\"a\":[1]},2]", R"(["a\u00e4","b"])"
+        };
+        for (const std::string& text : texts)
+        {
+            CAPTURE(text)
+            const json_document d = json_document::parse(text);
+            const json_view v = d.root();
+            const json expected = json::parse(text);
+            for (std::size_t i = 0; i < expected.size(); ++i)
+            {
+                CHECK(v[i].materialize() == expected[i]);
+                CHECK(v.at(i).materialize() == expected[i]);
+            }
+            CHECK(v[expected.size()].is_discarded());
+            if (!expected.empty())
+            {
+                CHECK(v.back().materialize() == expected.back());
+            }
+        }
+        // a long array (the direct lookup is not limited to short ones), also with a container at its end
+        std::string text = "[0";
+        for (int i = 1; i < 1000; ++i)
+        {
+            text += "," + std::to_string(i);
+        }
+        const json_document scalars = json_document::parse(text + "]");
+        CHECK(scalars.root()[999].get<int>() == 999);
+        CHECK(scalars.root()[500].get<int>() == 500);
+        CHECK(scalars.root().at(1).get<int>() == 1);
+        CHECK(scalars.root().back().get<int>() == 999);
+        const json_document container_last = json_document::parse(text + ",[1000]]");
+        CHECK(container_last.root()[999].get<int>() == 999);
+        CHECK(container_last.root()[1000][0].get<int>() == 1000);
+        CHECK(container_last.root().back()[0].get<int>() == 1000);
+    }
+
     SECTION("iterators")
     {
         const json_document d = json_document::parse(R"({"x":[1,{"y":2}],"z":null})");
@@ -1045,6 +1140,28 @@ TEST_CASE("json_view element access and iteration")
         CHECK((*first++).key() == "0");
         CHECK((*first).key() == "1");
         CHECK(++first == items.end());
+
+        // the keys of array elements are their indexes, whether or not they are asked for
+        std::string numbers = "[0";
+        for (int i = 1; i < 1234; ++i)
+        {
+            numbers += "," + std::to_string(i);
+        }
+        const json_document array = json_document::parse(numbers + "]");
+        std::size_t position = 0;
+        for (const auto& item : array.root().items())
+        {
+            CHECK(item.value().get<std::size_t>() == position);
+            if (position % 3 != 0) // (not for every item: values alone do not make the key)
+            {
+                CHECK(item.key() == std::to_string(position));
+                CHECK(item.key().data() == item.key().data()); // (the same text every time)
+                const json_view::item copy = item;
+                CHECK(copy.key() == std::to_string(position));
+            }
+            ++position;
+        }
+        CHECK(position == 1234);
 #ifdef JSON_HAS_CPP_17
         std::string pairs;
         for (const auto [key, value] : d.root().items())
@@ -1383,7 +1500,17 @@ TEST_CASE("json_view values")
         CHECK(exception_of([&] { static_cast<void>(v.value("s", 0)); }) == without_path(exception_of([&] { static_cast<void>(j.value("s", 0)); })));
         CHECK(exception_of([&] { static_cast<void>(v["n"].value("x", 0)); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value("x", 0)); })));
         CHECK(exception_of([&] { static_cast<void>(v["n"].value(json::json_pointer("/x"), 0)); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value(json::json_pointer("/x"), 0)); })));
+        // string defaults: the member is not a string, or the value is neither an object nor an array
+        CHECK(exception_of([&] { static_cast<void>(v.value("n", "default")); }) == without_path(exception_of([&] { static_cast<void>(j.value("n", "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v["n"].value("x", "default")); }) == without_path(exception_of([&] { static_cast<void>(j["n"].value("x", "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v.value(json::json_pointer("/n"), "default")); }) == without_path(exception_of([&] { static_cast<void>(j.value(json::json_pointer("/n"), "default")); })));
+        CHECK(exception_of([&] { static_cast<void>(v["s"].value(json::json_pointer("/x"), "default")); }) == without_path(exception_of([&] { static_cast<void>(j["s"].value(json::json_pointer("/x"), "default")); })));
 #endif
+        // (defaults and members longer than the short string optimization)
+        CHECK(v.value("s", "a default longer than fifteen characters") == "text");
+        CHECK(v.value("missing", "a default longer than fifteen characters") == "a default longer than fifteen characters");
+        CHECK(v.value(json::json_pointer("/s"), "a default longer than fifteen characters") == "text");
+        CHECK(v.value(json::json_pointer("/zz"), "a default longer than fifteen characters") == "a default longer than fifteen characters");
     }
 }
 

tests/src/unit-json_view_builder.cpp

@@ -523,6 +523,58 @@ TEST_CASE("json_view builder: strings across vector blocks")
     }
 }
 
+TEST_CASE("json_view builder: escapes between runs of text")
+{
+    // The text between escapes is copied 16 bytes at a time where there are
+    // that many bytes left, and with the UTF-8 check where there is
+    // non-ASCII text. Runs of every length from 0 to 40 between valid and
+    // invalid escapes, UTF-8 sequences, and control characters, in strings
+    // that are cut at all places near the end of the text.
+    const std::array<const char*, 9> valid = {{"\\n", "\\\"", "\\\\", "\\/", "\\t", "\\u00e4", "\\u20ac", "\\ud83d\\ude00", "\\u0000"}};
+    const std::array<const char*, 9> invalid = {{"\\x", "\\ud800", "\\udc00", "\\u12G4", "\\u12", "\\ud83dx", "\\ud83d\\u0041", "\\", "\x01"}};
+    const std::array<const char*, 6> utf8 = {{"\xc3\xa4", "\xe2\x82\xac", "\xf0\x9f\x98\x80", "\xc3", "\xff", "\x80"}};
+    std::mt19937 rng(2026); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
+    for (std::size_t run = 0; run <= 40; ++run)
+    {
+        for (int i = 0; i < 60; ++i)
+        {
+            std::string content = std::string(rng() % 20, 'a');
+            const auto pieces = 1 + (rng() % 6);
+            for (unsigned k = 0; k < pieces; ++k)
+            {
+                content += valid[rng() % valid.size()];
+                content += std::string(k == 0 ? run : rng() % 41, static_cast<char>('b' + (rng() % 20)));
+                switch (rng() % 8)
+                {
+                    case 0:
+                        content += utf8[rng() % 3];
+                        break;
+                    case 1:
+                        content += utf8[rng() % utf8.size()];
+                        break;
+                    case 2:
+                        content += invalid[rng() % invalid.size()];
+                        break;
+                    default:
+                        break;
+                }
+            }
+            check_string(content);
+            check_string(content.substr(0, content.size() - (rng() % 4)));
+        }
+    }
+    // the text before the first escape, and runs and escapes at the end of the text
+    for (std::size_t before = 0; before <= 40; ++before)
+    {
+        for (const char* escape : valid)
+        {
+            check_string(std::string(before, 'a') + escape);
+            check_string(std::string(before, 'a') + escape + std::string(before % 19, 'z'));
+            check_string(std::string(before, 'a') + escape + escape + std::string(before % 19, 'z'));
+        }
+    }
+}
+
 TEST_CASE("json_view node integer bits")
 {
     using nlohmann::detail::view::integer_bits;

tests/src/unit-json_view_dump.cpp

@@ -21,6 +21,7 @@ using nlohmann::ordered_json_view;
 using json_view_test::generator;
 using json_view_test::has_duplicate_keys;
 
+#include <algorithm>
 #include <array>
 #include <cmath>
 #include <cstddef>
@@ -29,6 +30,7 @@ using json_view_test::has_duplicate_keys;
 #include <iomanip>
 #include <map>
 #include <random>
+#include <set>
 #include <sstream>
 #include <string>
 #include <vector>
@@ -186,6 +188,133 @@ TEST_CASE("json_view dump")
         CHECK(deep_document.root().dump() == deep);
     }
 
+    SECTION("ensure_ascii: a character that needs an escape at each position of a string")
+    {
+        // string lengths around the width of the vector steps, in a string value, a key, and a value near the end of the text
+        for (const char* const special :
+                {
+                    "\xC3\xA9", "\xE4\xB8\xAD", "\xF0\x9F\x98\x80", "\x7F", "\\n", "\\u0001", "\\\"", "\\\\"
+                })
+        {
+            for (std::size_t length = 0; length <= 40; ++length)
+            {
+                for (std::size_t position = 0; position <= length; ++position)
+                {
+                    std::string content(length, 'a');
+                    content.insert(position, special);
+                    const std::array<std::string, 3> texts =
+                    {
+                        {
+                            "\"" + content + "\"",
+                            "[\"" + content + "\"]",
+                            "{\"" + content + "\":1}",
+                        }
+                    };
+                    for (const std::string& text : texts)
+                    {
+                        CAPTURE(text)
+                        const ordered_json_document d = ordered_json_document::parse(text);
+                        const ordered_json j = ordered_json::parse(text);
+                        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+                        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
+                        CHECK(d.root().dump() == j.dump());
+                    }
+                }
+            }
+        }
+    }
+
+    SECTION("ensure_ascii: every character of the Basic Multilingual Plane and some beyond")
+    {
+        // (the two- and three-byte sequences, including the ranges that need a check: E0, ED, EF BF BF)
+        std::string text = "[";
+        std::size_t in_chunk = 0;
+        const auto append = [&](std::uint32_t cp)
+        {
+            if (cp < 0x80)
+            {
+                if (cp < 0x20 || cp == '"' || cp == '\\')
+                {
+                    return;
+                }
+                text += static_cast<char>(cp);
+            }
+            else if (cp < 0x800)
+            {
+                text += static_cast<char>(0xC0 | (cp >> 6));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+            else if (cp < 0x10000)
+            {
+                text += static_cast<char>(0xE0 | (cp >> 12));
+                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+            else
+            {
+                text += static_cast<char>(0xF0 | (cp >> 18));
+                text += static_cast<char>(0x80 | ((cp >> 12) & 0x3F));
+                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+        };
+        for (std::uint32_t cp = 0x20; cp < 0x10400; ++cp)
+        {
+            if (cp >= 0xD800 && cp < 0xE000)
+            {
+                continue;
+            }
+            if (in_chunk == 0)
+            {
+                text += text.size() > 1 ? ",\"" : "\"";
+            }
+            append(cp);
+            if (++in_chunk == 37)
+            {
+                text += "\"";
+                in_chunk = 0;
+            }
+        }
+        text += in_chunk != 0 ? "\"]" : "]";
+        const ordered_json_document d = ordered_json_document::parse(text);
+        const ordered_json j = ordered_json::parse(text);
+        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
+        CHECK(d.root().dump() == j.dump());
+        CHECK(d.root().dump(2) == j.dump(2));
+    }
+
+    SECTION("deep nesting, indented")
+    {
+        // indentations of up to and beyond the width of the writer's fixed-size copy
+        for (const int depth :
+                {
+                    1, 5, 20, 70, 300
+                })
+        {
+            std::string text;
+            for (int i = 0; i < depth; ++i)
+            {
+                text += i % 2 == 0 ? "[1," : R"({"k":2,"\u00e9":)";
+            }
+            text += "[]";
+            for (int i = depth - 1; i >= 0; --i)
+            {
+                text += i % 2 == 0 ? "]" : "}";
+            }
+            const ordered_json_document d = ordered_json_document::parse(text);
+            const ordered_json j = ordered_json::parse(text);
+            for (const int indent :
+                    {
+                        0, 1, 2, 3, 8
+                    })
+            {
+                CHECK(d.root().dump(indent) == j.dump(indent));
+                CHECK(d.root().dump(indent, '\t') == j.dump(indent, '\t'));
+            }
+        }
+    }
+
     SECTION("the output buffer of a small value is small")
     {
         // an escaped key after the value: its node lies in the arena, so the
@@ -598,6 +727,152 @@ TEST_CASE("json_view large objects")
         CHECK(without_collisions.memory_usage() >= with_collisions.memory_usage() + (table_size * sizeof(std::uint32_t)));
     }
 
+    SECTION("keys that differ in their last bytes are spread over the table")
+    {
+        // The hash must spread the usual families of keys (numbered names, hex
+        // strings, dates, short names): a key farther than index_max_displacement
+        // from its home slot would leave the object without a table. The keys
+        // are placed with linear probing, as the table does.
+        const auto max_displacement = [](const std::vector<std::string>& keys)
+        {
+            std::size_t slots = 16;
+            while (slots < 2 * keys.size())
+            {
+                slots *= 2;
+            }
+            std::vector<bool> used(slots, false);
+            std::size_t farthest = 0;
+            for (const std::string& key : keys)
+            {
+                std::size_t i = nlohmann::detail::conditional_static_cast<std::size_t>(nlohmann::detail::view::key_hash(key.data(), key.size())) & (slots - 1);
+                std::size_t distance = 0;
+                while (used[i])
+                {
+                    i = (i + 1) & (slots - 1);
+                    ++distance;
+                }
+                used[i] = true;
+                farthest = (std::max)(farthest, distance);
+            }
+            return farthest;
+        };
+        // the keys of a printf-like pattern with one %d, %0Nd or %0Nx, formatted with a stream
+        // (a format string that is not a literal is a Flawfinder error)
+        const auto numbered = [](const char* format, int count, int step)
+        {
+            const std::string pattern(format);
+            const std::size_t percent = pattern.find('%');
+            std::size_t conversion = percent + 1;
+            std::size_t width = 0;
+            while (pattern[conversion] >= '0' && pattern[conversion] <= '9')
+            {
+                width = (width * 10) + static_cast<std::size_t>(pattern[conversion] - '0');
+                ++conversion;
+            }
+            const bool hex = pattern[conversion] == 'x';
+            std::vector<std::string> keys;
+            for (int i = 0; i < count; ++i)
+            {
+                std::ostringstream key;
+                key << pattern.substr(0, percent) << std::setfill('0') << std::setw(static_cast<int>(width))
+                    << (hex ? std::hex : std::dec) << (i * step) << pattern.substr(conversion + 1);
+                keys.push_back(key.str());
+            }
+            return keys;
+        };
+        for (const char* format :
+                {"key%d", "%d", "item_%04d", "a%05d", "%03dxyz", "id%d", "user_%d", "%d_suffix", "0x%04x", "A%07d", "12345678%d", "1234567%d", "123456789%d",
+                 "configuration_parameter_value_%04d_extra", "2026-01-%02dT00:00:00Z"
+                })
+        {
+            CAPTURE(format)
+            CHECK(max_displacement(numbered(format, std::string(format).find("%02d") != std::string::npos ? 60 : 1000, 1)) < nlohmann::detail::view::index_max_displacement); // NOLINT(abseil-string-find-str-contains)
+            CHECK(max_displacement(numbered(format, 600, 7)) < nlohmann::detail::view::index_max_displacement);
+        }
+        std::mt19937_64 rng(7); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        for (const std::size_t length :
+                {
+                    std::size_t{1}, std::size_t{2}, std::size_t{3}, std::size_t{5}, std::size_t{7}, std::size_t{8}, std::size_t{9}, std::size_t{12}, std::size_t{16}, std::size_t{17}, std::size_t{33}
+                })
+        {
+            CAPTURE(length)
+            std::set<std::string> distinct;
+            // (there are 26 and 676 keys of one and two letters)
+            std::size_t wanted = 700;
+            if (length == 1)
+            {
+                wanted = 26;
+            }
+            else if (length == 2)
+            {
+                wanted = 500;
+            }
+            while (distinct.size() < wanted)
+            {
+                std::string key(length, 'a');
+                for (char& c : key)
+                {
+                    c = static_cast<char>('a' + (rng() % 26));
+                }
+                distinct.insert(key);
+            }
+            CHECK(max_displacement(std::vector<std::string>(distinct.begin(), distinct.end())) < nlohmann::detail::view::index_max_displacement);
+        }
+    }
+
+    SECTION("keys of every length that differ in one byte")
+    {
+        // In a large object, a key is found by comparing its bytes with those of the member the
+        // table points to: up to 16 bytes as two overlapping words, longer ones with memcmp.
+        // Keys of every length from 0 to 40, and keys that differ from them in one byte.
+        std::mt19937_64 rng(2026); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        std::vector<std::string> keys;
+        std::set<std::string> distinct;
+        for (std::size_t length = 0; length <= 40; ++length)
+        {
+            for (int copy = 0; copy < 5; ++copy)
+            {
+                std::string key(length, 'a');
+                for (char& c : key)
+                {
+                    c = static_cast<char>('a' + (rng() % 26));
+                }
+                if (distinct.insert(key).second)
+                {
+                    keys.push_back(key);
+                }
+            }
+        }
+        std::string text = "{";
+        for (std::size_t i = 0; i < keys.size(); ++i)
+        {
+            text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i);
+        }
+        text += "}";
+        REQUIRE(keys.size() >= 128); // (a table is built for 128 members)
+        const json_document d = json_document::parse(text);
+        const json_view v = d.root();
+        for (std::size_t i = 0; i < keys.size(); ++i)
+        {
+            CAPTURE(keys[i])
+            CHECK(v[keys[i]].get<std::size_t>() == i);
+            CHECK(v.at(keys[i]).get<std::size_t>() == i);
+            CHECK(v.contains(keys[i]));
+            for (std::size_t at = 0; at < keys[i].size(); ++at)
+            {
+                std::string other = keys[i];
+                other[at] = other[at] == 'z' ? 'y' : 'z';
+                CAPTURE(other)
+                CHECK(v.contains(other) == (distinct.count(other) != 0));
+            }
+            CHECK(v.contains(keys[i] + "a") == (distinct.count(keys[i] + "a") != 0));
+            if (!keys[i].empty())
+            {
+                CHECK(v.contains(keys[i].substr(1)) == (distinct.count(keys[i].substr(1)) != 0));
+            }
+        }
+    }
+
     SECTION("shrink_to_fit releases the tables' spare capacity")
     {
         const auto make_text = [](int objects, int members)

tests/src/unit-json_view_edit.cpp

@@ -661,6 +661,115 @@ TEST_CASE("json_view edits: replacing arrays and objects by scalars")
     CHECK(d.root().materialize() == expected);
 }
 
+TEST_CASE("json_view edits: arrays whose elements have no subtrees")
+{
+    // such an array is indexed directly while it is in its parsed layout; edits
+    // that replace elements by scalars keep it, others move it
+    json_editable_document d = json_editable_document::parse("[10,20,30,40]");
+    json expected = json::array({10, 20, 30, 40});
+    const auto check = [&]
+    {
+        CHECK(d.root().size() == expected.size());
+        for (std::size_t i = 0; i < expected.size(); ++i)
+        {
+            CHECK(d.root()[i].materialize() == expected[i]);
+            CHECK(d.root().at(i).materialize() == expected[i]);
+        }
+        CHECK(d.root()[expected.size()].is_discarded());
+        CHECK(d.root().back().materialize() == expected.back());
+        CHECK(d.root().dump() == expected.dump());
+    };
+    check();
+    d.set(d.root()[1], "x");
+    expected[1] = "x";
+    check();
+    d.set(d.root()[3], 2.5);
+    expected[3] = 2.5;
+    check();
+    d.set(d.root()[2], json::array({1, 2}));
+    expected[2] = json::array({1, 2});
+    check();
+    d.push_back(d.root(), 50);
+    expected.push_back(50);
+    check();
+    d.insert(d.root(), 0, true);
+    expected.insert(expected.begin(), true);
+    check();
+    d.erase(d.root(), 1);
+    expected.erase(expected.begin() + 1);
+    check();
+    d.set(d.root()[2], nullptr);
+    expected[2] = nullptr;
+    check();
+}
+
+TEST_CASE("json_view edits: materializing values nested deeper than the document was parsed")
+{
+    // the stack of open containers of materialize() is sized from the nesting of the parsed text;
+    // a value added by an edit can be deeper than that (and than the stack that is local to the call)
+    json_editable_document d = json_editable_document::parse("[1,[2]]");
+    json expected = json::array({1, json::array({2})});
+    json nested = 3;
+    for (int level = 0; level < 40; ++level)
+    {
+        nested = json::array({nested, json{{"k", level}}});
+    }
+    d.push_back(d.root(), nested);
+    expected.push_back(nested);
+    CHECK(d.root().materialize() == expected);
+    CHECK(d.root()[2].materialize() == nested);
+    d.set(d.root()[1][0], nested);
+    expected[1][0] = nested;
+    CHECK(d.root().materialize() == expected);
+    CHECK(d.root().get<json>() == expected);
+}
+
+TEST_CASE("json_view edits: an editable document before and after its first edit")
+{
+    // until the first edit, an editable document is read like a read-only one; views made before the edit
+    // keep working after it
+    const std::string text = R"({"a":[1,2,{"x":"y"},4],"b":{"c":true,"d":null},"e":"text","f":[]})";
+    const json_document read_only = json_document::parse(text);
+    json_editable_document d = json_editable_document::parse(text);
+    const auto root = d.root();
+    const auto same_as_read_only = [&]
+    {
+        CHECK(root.dump() == read_only.root().dump());
+        CHECK(root.dump(2) == read_only.root().dump(2));
+        CHECK(root.materialize() == read_only.root().materialize());
+        CHECK(root["a"][2]["x"].get_string() == "y");
+        CHECK(root["a"].at(3).get<int>() == 4);
+        CHECK(root["a"].back().get<int>() == 4);
+        CHECK(root.contains("b"));
+        CHECK(!root.contains("zz"));
+        CHECK(root.find("e")->get_string() == "text");
+        CHECK(root.find("zz") == root.end());
+        CHECK(root["b"]["c"].get<bool>());
+        CHECK(root.value("e", "none") == "text");
+        std::size_t count = 0;
+        for (const auto m : root["a"])
+        {
+            CHECK(m.materialize() == read_only.root()["a"][count].materialize());
+            ++count;
+        }
+        CHECK(count == 4);
+    };
+    same_as_read_only();
+    // an edit that changes a scalar in place, then one that moves an array
+    d.set(root["e"], "other");
+    CHECK(root["e"].get_string() == "other");
+    CHECK(root["a"][2]["x"].get_string() == "y");
+    CHECK(root["a"].back().get<int>() == 4);
+    d.push_back(root["f"], 7);
+    CHECK(root["f"][0].get<int>() == 7);
+    CHECK(root["f"].back().get<int>() == 7);
+    CHECK(root.dump() == R"({"a":[1,2,{"x":"y"},4],"b":{"c":true,"d":null},"e":"other","f":[7]})");
+    d.set(root["a"], 2, json::array({1, 2}));
+    CHECK(root["a"][2][1].get<int>() == 2);
+    CHECK(root["a"].dump() == "[1,2,[1,2],4]");
+    CHECK(root.materialize() == json::parse(R"({"a":[1,2,[1,2],4],"b":{"c":true,"d":null},"e":"other","f":[7]})"));
+}
+
 namespace
 {
 // reads of "a" in an object that repeats it: the first member wins, however the

tests/src/unit-json_view_image.cpp

@@ -682,6 +682,26 @@ TEST_CASE("json_view images: ownership")
 #if !defined(JSON_NOEXCEPTION)
 TEST_CASE("json_view images: errors")
 {
+    SECTION("invalid UTF-8 of a decoded string: the compact dump writes it, the others throw")
+    {
+        const json_document d = json_document::parse(R"({"k\n":"\u00e9x"})");
+        std::vector<std::uint8_t> image = d.save();
+        const std::size_t arena = text_at(image) + header_size_field(image, 16) + 1;
+        image[arena + 3] = 0x28; // the key is "k\n"; the value starts at 3: 0xC3 0x28 is invalid
+        const json_document loaded = json_document::load(image, image_check::bounds);
+        CHECK(loaded.root().dump().size() == 13);
+        for (const int indent :
+                {
+                    0, 2
+                })
+        {
+            CHECK_THROWS_AS(loaded.root().dump(indent), json::type_error);
+            CHECK_THROWS_AS(loaded.root().dump(indent, ' ', true), json::type_error);
+        }
+        CHECK_THROWS_AS(loaded.root().dump(-1, ' ', true), json::type_error);
+        CHECK_THROWS_WITH_AS(loaded.root().dump(2), "[json.exception.type_error.316] invalid UTF-8 byte at index 1: 0x28", json::type_error&);
+    }
+
     SECTION("a literal as the root: dump() after loading")
     {
         for (const char* text :

tests/src/unit-ordered_json.cpp

@@ -12,6 +12,11 @@
 using nlohmann::json;
 using nlohmann::ordered_json;
 
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <string>
+
 TEST_CASE("ordered_json")
 {
     json j;
@@ -237,3 +242,276 @@ TEST_CASE("regression test for issue #5673 - ordered_json::emplace with a non-rv
         CHECK(oj.dump() == "{\"a\":1}");
     }
 }
+
+namespace
+{
+// the sizes around which the DOM parser changes how it stores the elements of
+// an array (16) and the members of an object in a vector (32, and 64 for the
+// key index)
+const std::array<std::size_t, 17> container_sizes = {{0, 1, 2, 3, 15, 16, 17, 18, 31, 32, 33, 34, 63, 64, 65, 66, 200}};
+
+template<typename Json>
+std::string array_text(const std::size_t n, const std::size_t depth)
+{
+    std::string text = "[";
+    for (std::size_t i = 0; i < n; ++i)
+    {
+        text += (i == 0 ? "" : ",");
+        // alternate scalars, empty containers and nested containers
+        switch (i % 4)
+        {
+            case 0:
+                text += std::to_string(i);
+                break;
+            case 1:
+                text += "\"s" + std::to_string(i) + "\"";
+                break;
+            case 2:
+                text += depth == 0 ? "[]" : array_text<Json>(n / 2, depth - 1);
+                break;
+            default:
+                text += depth == 0 ? "{}" : "{\"a\":" + array_text<Json>(n / 3, depth - 1) + ",\"b\":null}";
+                break;
+        }
+    }
+    return text + "]";
+}
+
+template<typename Json>
+std::string object_text(const std::size_t n, const std::size_t depth, const bool duplicates)
+{
+    std::string text = "{";
+    for (std::size_t i = 0; i < n; ++i)
+    {
+        text += (i == 0 ? "" : ",");
+        text += "\"key" + std::to_string(i) + "\":";
+        switch (i % 4)
+        {
+            case 0:
+                text += std::to_string(i);
+                break;
+            case 1:
+                text += depth == 0 ? "[]" : array_text<Json>(n / 2, depth - 1);
+                break;
+            case 2:
+                text += depth == 0 ? "{}" : object_text<Json>(n / 2, depth - 1, duplicates);
+                break;
+            default:
+                text += "\"value\"";
+                break;
+        }
+    }
+    if (duplicates)
+    {
+        // keys that are there already, the first and the last one, with other values
+        text += n == 0 ? "" : ",";
+        text += R"("key0":[1,2],"key)";
+        text += std::to_string(n - 1);
+        text += R"(":{"again":true})";
+    }
+    return text + "}";
+}
+
+template<typename Json>
+void check_same_dump(const std::string& text)
+{
+    // the text is what dump() writes for the parsed value, and the value
+    // survives a second round trip: arrays keep their elements in order, an
+    // ordered_json keeps its members in order of appearance
+    const Json parsed = Json::parse(text);
+    const Json again = Json::parse(parsed.dump());
+    CHECK(parsed == again);
+    CHECK(parsed.dump() == again.dump());
+    CHECK(Json::accept(text));
+}
+} // namespace
+
+TEST_CASE("parsing containers of sizes around the limits of the DOM parser")
+{
+    SECTION("arrays")
+    {
+        for (const std::size_t n : container_sizes)
+        {
+            const std::string text = array_text<json>(n, 2);
+            INFO("size ", n);
+
+            const json parsed = json::parse(text);
+            CHECK(parsed.is_array());
+            CHECK(parsed.size() == n);
+            for (std::size_t i = 0; i < n; i += 4)
+            {
+                CHECK(parsed[i] == i);
+            }
+            check_same_dump<json>(text);
+            check_same_dump<ordered_json>(text);
+            CHECK(ordered_json::parse(text).dump() == parsed.dump());
+        }
+    }
+
+    SECTION("objects")
+    {
+        for (const bool duplicates :
+                {
+                    false, true
+                })
+        {
+            for (const std::size_t n : container_sizes)
+            {
+                const std::string text = object_text<json>(n, 2, duplicates);
+                INFO("size ", n, " duplicates ", duplicates);
+
+                const json parsed = json::parse(text);
+                const ordered_json ordered = ordered_json::parse(text);
+                CHECK(parsed.is_object());
+                CHECK(ordered.is_object());
+                CHECK(parsed.size() == ordered.size());
+                // the same members, in the order of their first appearance
+                std::size_t i = 0;
+                for (auto it = ordered.begin(); it != ordered.end(); ++it, ++i)
+                {
+                    if (i < n)
+                    {
+                        CHECK(it.key() == "key" + std::to_string(i));
+                    }
+                    CHECK(parsed.at(it.key()) == json(it.value()));
+                }
+                if (duplicates && n > 1)
+                {
+                    // the later value replaced the earlier one in its place
+                    CHECK(ordered.at("key0") == ordered_json::parse("[1,2]"));
+                    CHECK(ordered.at("key" + std::to_string(n - 1)) == ordered_json::parse("{\"again\":true}"));
+                    CHECK(ordered.begin().key() == "key0");
+                    CHECK(ordered.size() == n);
+                }
+                check_same_dump<json>(text);
+                check_same_dump<ordered_json>(text);
+            }
+        }
+    }
+
+    SECTION("objects with many different and repeated keys")
+    {
+        // 300 members of which a third repeat an earlier key
+        std::string text = "{";
+        for (std::size_t i = 0; i < 300; ++i)
+        {
+            text += (i == 0 ? "" : ",");
+            text += "\"k" + std::to_string(i % 200) + "\":" + std::to_string(i);
+        }
+        text += '}';
+
+        const ordered_json ordered = ordered_json::parse(text);
+        const json parsed = json::parse(text);
+        CHECK(ordered.size() == 200);
+        CHECK(parsed.size() == 200);
+        std::size_t i = 0;
+        for (auto it = ordered.begin(); it != ordered.end(); ++it, ++i)
+        {
+            CHECK(it.key() == "k" + std::to_string(i));
+            // the last value written
+            CHECK(it.value() == (i < 100 ? i + 200 : i));
+            CHECK(parsed.at(it.key()) == json(it.value()));
+        }
+    }
+}
+
+namespace
+{
+// a deterministic source of structure for parsing tests: builds a JSON text
+// and, at the same time, the value it has to parse to
+class tree_generator
+{
+  public:
+    explicit tree_generator(std::uint32_t seed) : state(seed) {}
+
+    template<typename Json>
+    Json make(std::string& text, const std::size_t depth)
+    {
+        switch (next(depth == 0 ? 5 : 9))
+        {
+            case 0:
+                text += "null";
+                return Json(nullptr);
+            case 1:
+                text += "true";
+                return Json(true);
+            case 2:
+            {
+                const int n = static_cast<int>(next(2000)) - 1000;
+                text += std::to_string(n);
+                return Json(n);
+            }
+            case 3:
+                text += "\"text\"";
+                return Json("text");
+            case 4:
+                text += "2.5";
+                return Json(2.5);
+            case 5:
+            case 6:
+            case 7:
+            {
+                Json array = Json::array();
+                text += '[';
+                const std::size_t n = size();
+                for (std::size_t i = 0; i < n; ++i)
+                {
+                    text += (i == 0 ? "" : ",");
+                    array.push_back(make<Json>(text, depth - 1));
+                }
+                text += ']';
+                return array;
+            }
+            default:
+            {
+                Json object = Json::object();
+                text += '{';
+                const std::size_t n = size();
+                for (std::size_t i = 0; i < n; ++i)
+                {
+                    const std::string key = "k" + std::to_string(i);
+                    text += (i == 0 ? "\"" : ",\"") + key + "\":";
+                    object[key] = make<Json>(text, depth - 1);
+                }
+                text += '}';
+                return object;
+            }
+        }
+    }
+
+  private:
+    std::uint32_t next(const std::uint32_t bound)
+    {
+        state = (state * 1664525U) + 1013904223U;
+        return (state >> 8) % bound;
+    }
+
+    std::size_t size()
+    {
+        return container_sizes[next(static_cast<std::uint32_t>(container_sizes.size()))];
+    }
+
+    std::uint32_t state;
+};
+} // namespace
+
+TEST_CASE("parsing random trees of arrays and objects")
+{
+    for (std::uint32_t seed = 1; seed <= 150; ++seed)
+    {
+        INFO("seed ", seed);
+
+        std::string text;
+        std::string ordered_text;
+        const json expected = tree_generator(seed).make<json>(text, 3);
+        const auto ordered_expected = tree_generator(seed).make<ordered_json>(ordered_text, 3);
+        CHECK(text == ordered_text);
+
+        CHECK(json::parse(text) == expected);
+        CHECK(json::accept(text));
+        const ordered_json ordered = ordered_json::parse(text);
+        CHECK(ordered == ordered_expected);
+        CHECK(ordered.dump() == ordered_expected.dump());
+        CHECK(json::parse(text).dump() == expected.dump());
+    }
+}