Merge branch 'json-view/22-view-dump-fast' into json-view/15-view-bench

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

.gitignore

@@ -47,3 +47,6 @@ nlohmann_json.spdx
 
 # Bazel-related
 MODULE.bazel.lock
+
+# GCC module cache
+/gcm.cache/

README.md

@@ -1402,7 +1402,7 @@ THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR I
 
 - The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2008-2009 [Björn Hoehrmann](https://bjoern.hoehrmann.de/) <bjoern@hoehrmann.de>
 - The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2009 [Florian Loitsch](https://florian.loitsch.com/)
-- The class contains a port of the shortest double-to-decimal conversion of [Żmij](https://github.com/vitaut/zmij) by Victor Zverovich, which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2025 [Victor Zverovich](https://github.com/vitaut)
+- The class contains a port of the shortest double-to-decimal conversion of [Żmij](https://github.com/vitaut/zmij) by Victor Zverovich, including the conversion of the digits to text by Xiang JunBo and the SIMD instruction sequence of Dougall Johnson, which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright &copy; 2025 [Victor Zverovich](https://github.com/vitaut)
 - The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).
 - The class contains parts of [Google Abseil](https://github.com/abseil/abseil-cpp) which is licensed under the [Apache 2.0 License](https://opensource.org/licenses/Apache-2.0).
 - The class contains an adapted version of the Eisel-Lemire algorithm, its table of powers of five, and its digit comparison for long numbers from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright &copy; 2021 The fast_float authors

docs/docset/docSet.sql

@@ -186,7 +186,6 @@ INSERT INTO searchIndex(name, type, path) VALUES ('basic_json_view::items', 'Met
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json_view::materialize', 'Method', 'api/basic_json_view/materialize/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json_view::number_format', 'Enum', 'api/basic_json_view/number_format/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json_view::number_token', 'Method', 'api/basic_json_view/number_token/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('basic_json_view::operator bool', 'Method', 'api/basic_json_view/operator_bool/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json_view::operator<<', 'Operator', 'api/basic_json_view/operator_ltlt/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json_view::operator[]', 'Operator', 'api/basic_json_view/operator[]/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json_view::operator==', 'Operator', 'api/basic_json_view/operator_eq/index.html');

docs/mkdocs/docs/api/basic_json/number_float_t.md

@@ -23,10 +23,10 @@ type to use.
 ## Template parameters
 
 `NumberFloatType`
-:   the type to store floating-point numbers. The parser converts `#!cpp float`, `#!cpp double`, and a
-    `#!cpp long double` that is IEEE 754 binary64 itself and other `#!cpp long double` formats with
-    `#!cpp std::from_chars` or `#!cpp std::strtold`, and serialization falls back to `#!cpp std::snprintf`, so the
-    type must be `#!cpp float`, `#!cpp double`, or `#!cpp long double`. The
+:   the type to store floating-point numbers. The type must be `#!cpp float`, `#!cpp double`, or
+    `#!cpp long double`. The parser converts `#!cpp float`, `#!cpp double`, and a `#!cpp long double` that is IEEE 754
+    binary64 itself. It converts other `#!cpp long double` formats with `#!cpp std::from_chars` where available, or
+    with `#!cpp std::strtold` otherwise. Serialization falls back to `#!cpp std::snprintf`. The
     [binary formats](../../features/binary_formats/index.md) additionally require `#!cpp float` or `#!cpp double`,
     because they have no encoding for `#!cpp long double`. See
     [Template Parameter Requirements](../../features/types/template_parameters.md#numberfloattype).

docs/mkdocs/docs/api/basic_json_document/accept.md

@@ -43,6 +43,11 @@ input's own copy (for inputs that are always read into a buffer) throws.
 
 Linear in the length of the input.
 
+## Notes
+
+An integer argument that is not a `#!cpp bool` where the flags are expected, such as `#!cpp accept(ptr, len)`, does not
+compile; see [`parse`](parse.md#notes).
+
 ## Examples
 
 ??? example

docs/mkdocs/docs/api/basic_json_document/erase.md

@@ -86,8 +86,8 @@ view of a *different* document (overloads 1-2 only; overload 3 always starts fro
 
 !!! info "Duplicate keys"
 
-    Overload 1. removes *every* member with `key`, not just the first -- unlike [`set`](set.md), which assigns the
-    first occurrence and drops the rest. This is why it returns a count rather than a single view: there may be
+    Overload 1. removes *every* member with `key`, not just the last one that lookups find -- unlike [`set`](set.md),
+    which assigns that member and drops the rest. This is why it returns a count rather than a single view: there may be
     more than one member removed, or none.
 
 Like [`set`](set.md) and [`push_back`](push_back.md), `erase` never moves an element's *value*: a view still

docs/mkdocs/docs/api/basic_json_document/index.md

@@ -48,6 +48,7 @@ bookkeeping edits need, and calling any of them on one fails to compile (`#!cpp
 
 - **view_type** - the type of view returned by [`root()`](root.md) (`#!cpp basic_json_view<BasicJsonType, Editable>`)
 - **value_t** - the JSON type enumeration, see [`basic_json::value_t`](../basic_json/value_t.md)
+- **image_check** - how [`load()`](load.md) validates an image (`full`, `bounds`, `none`), see [`image_check`](load.md#image_check)
 
 ## Member functions
 

docs/mkdocs/docs/api/basic_json_document/load.md

@@ -85,9 +85,13 @@ Otherwise throws [`parse_error.116`](../../home/exceptions.md#jsonexceptionparse
 
 ## Complexity
 
-Linear in the number of nodes, which are always copied into the document. With `#!cpp check == image_check::full`,
-additionally linear in the combined length of the text and the decoded strings; `#!cpp image_check::bounds` and
-`#!cpp image_check::none` do not read them.
+Linear in the number of nodes, which are always copied into the document. `#!cpp image_check::none` does not read
+the text or the decoded strings. `#!cpp image_check::bounds` reads one byte of the text for each float token (its sign,
+to check the recorded digits against the token's length), and nothing else of the text or the decoded strings.
+
+With `#!cpp image_check::full`, linear in the size of the image (the nodes, the text, and the decoded strings), plus
+sorting the ranges of the strings and of the float tokens (at most one per node): the contents of each distinct range
+are checked once, however many nodes refer to it.
 
 ## Notes
 
@@ -108,7 +112,7 @@ How thoroughly `load()` validates `image` before trusting it.
 
 | value    | checks                                                                                                    | guarantees |
 |----------|--------------------------------------------------------------------------------------------------------------|------------|
-| `full`   | everything the parser itself guarantees: structure and bounds; that every string is valid UTF-8 (and, for a string still in the source text, that it contains no quote, backslash, or control character); and that every number token is well-formed and matches the value stored for it | reading and serializing a checked image is safe and always produces valid JSON, exactly as for a parsed document |
+| `full`   | everything the parser itself guarantees: structure and bounds; that every string is valid UTF-8 (and, for a string still in the source text, that it contains no quote, backslash, or control character); and that every number token is well-formed and matches the value stored for it; strings and float tokens may share a range only if the ranges are identical (as nodes that share a value do), and never overlap otherwise | reading and serializing a checked image is safe and always produces valid JSON, exactly as for a parsed document |
 | `bounds` | structure and bounds only -- that every offset and count in the node index stays inside the image            | reading and serializing stay memory-safe, but a crafted image can hold strings that are not valid UTF-8 or that serialize to invalid JSON ([`dump()`](../basic_json_view/dump.md) writes them unchanged or throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316)), and numbers whose values differ from their text |
 | `none`   | nothing                                                                                                       | images from a trusted source only -- reading a damaged image is undefined behavior |
 
@@ -136,6 +140,9 @@ so those stay safe on a damaged one. It does *not* guarantee that the image desc
 that a `full` check would have rejected can make [`dump()`](../basic_json_view/dump.md) write invalid UTF-8 or invalid
 JSON, or throw `type_error.316`, and a number can read back with a value that does not match how it is spelled.
 Reserve `bounds` for images you already trust to be well-formed, and use it only to skip the extra scan.
+An [editable document](../json_editable_document.md) does not take such a string over either:
+[`set`](set.md), [`push_back`](push_back.md) and [`insert`](insert.md) throw `type_error.316` when they copy it from
+a view of the loaded document, and leave the editable document unchanged.
 
 ## Examples
 

docs/mkdocs/docs/api/basic_json_document/parse.md

@@ -19,24 +19,33 @@ static basic_json_document parse(IteratorType first, IteratorType last,
 1. Deserialize from a compatible input, borrowing or owning it depending on its value category and type (see Notes).
 2. Deserialize from a pair of input iterators.
 
-Both overloads accept exactly what [`BasicJsonType::parse()`](../basic_json/parse.md) accepts, with the same
+Both overloads accept the same JSON text as [`BasicJsonType::parse()`](../basic_json/parse.md), with the same
 `ignore_comments`/`ignore_trailing_commas` options, but build a [`basic_json_document`](index.md) (a flat index into
-the input) instead of a tree of `BasicJsonType` values.
+the input) instead of a tree of `BasicJsonType` values. The input must be byte-oriented (see the template parameters
+below): not every input type of `BasicJsonType::parse()` is supported.
 
 ## Template parameters
 
 `InputType`
-:   A compatible input, for instance:
+:   A byte-oriented input, one of:
 
-    - a `#!cpp std::string`, `#!cpp std::string_view`, or a C-style array of characters
-    - a pointer to a null-terminated string of single byte characters
+    - a `#!cpp std::string`, `#!cpp std::string_view`, or a C-style array of single-byte characters
+    - a pointer to a null-terminated string of single-byte characters (`#!cpp char`, `#!cpp signed char`,
+      `#!cpp unsigned char`, `#!cpp std::uint8_t`)
     - a container for which `#!cpp obj.data()` and `#!cpp obj.size()` give contiguous single-byte access, e.g.
       `#!cpp std::vector<char>` or `#!cpp std::vector<std::uint8_t>`
-    - an `#!cpp std::istream` object, or anything else [`BasicJsonType::parse()`](../basic_json/parse.md) accepts
+    - an `#!cpp std::istream` object
+    - a wide string object (`#!cpp std::wstring`, `#!cpp std::u16string`, `#!cpp std::u32string`), which is converted
+      to UTF-8
+
+    Other inputs are not supported: a `#!cpp FILE*`, and pointers to or arrays of wide characters (`#!cpp wchar_t`,
+    `#!cpp char16_t`, `#!cpp char32_t`) are rejected at compile time by a `#!cpp static_assert`. (Use
+    [`BasicJsonType::parse()`](../basic_json/parse.md) for these.)
 
 `IteratorType`
-:   a compatible iterator type, for instance a pair of pointers such as `ptr` and `ptr + len`, or a pair of
-    `#!cpp std::string::iterator`
+:   an input iterator type, for instance a pair of pointers such as `ptr` and `ptr + len`, or a pair of
+    `#!cpp std::string::iterator`; the iterators of single-byte characters are borrowed or read like the byte inputs
+    above, those of wide characters are converted to UTF-8
 
 ## Parameters
 
@@ -70,8 +79,8 @@ discarded; see [`is_discarded`](is_discarded.md).
 Throws the same exception [`BasicJsonType::parse()`](../basic_json/parse.md) throws for the same input and options --
 the same exception id, message, and position -- because on a failing input the library's own parser is run on the
 same bytes to produce the diagnostic. Additionally throws
-[`out_of_range.416`](../../home/exceptions.md#jsonexceptionout_of_range416) if the input is 4 GiB or larger, a size
-[`BasicJsonType::parse()`](../basic_json/parse.md) does not reject.
+[`out_of_range.416`](../../home/exceptions.md#jsonexceptionout_of_range416) if the input is 4294967280 bytes (4 GiB
+minus 16 bytes) or larger, a size [`BasicJsonType::parse()`](../basic_json/parse.md) does not reject.
 
 ## Complexity
 
@@ -84,8 +93,8 @@ Linear in the length of the input.
 | `input`                                                                             | ownership                                                    |
 |--------------------------------------------------------------------------------------|--------------------------------------------------------------|
 | lvalue byte container (`std::string`, `std::vector<char>`, ...), `std::string_view`, C string, character array | **borrowed** -- `input` must outlive the document |
-| rvalue `#!cpp std::string`                                                            | **owned**, moved in without a copy                            |
-| rvalue byte container other than `#!cpp std::string`                                  | **owned**, copied                                             |
+| non-const rvalue `#!cpp std::string`                                                  | **owned**, moved in without a copy                            |
+| other rvalue byte container (including a `#!cpp const` rvalue `#!cpp std::string`)  | **owned**, copied                                             |
 | stream, wide string, or anything else read through the general input adapter          | **owned**, read into a buffer (a stream is read to its end)   |
 
 For overload (2), a pair of pointers to single-byte integers (e.g. `#!cpp const char*`, `#!cpp std::uint8_t*`) is
@@ -100,6 +109,12 @@ See [`owns_source`](owns_source.md) to check which happened after a call, and th
 **Numbers.** As for [`BasicJsonType::parse()`](../basic_json/parse.md), an integer literal too large for the 64-bit
 integer type becomes a floating-point value.
 
+**No lengths.** An integer argument that is not a `#!cpp bool` where the flags are expected -- for example
+`#!cpp parse(ptr, len)` -- does not compile (the overload is deleted). Such a call would convert `len` to
+`allow_exceptions` and read `ptr` as a null-terminated string, past the end of a buffer that has none. To parse a
+buffer of a given length, pass a pair of pointers: `#!cpp parse(ptr, ptr + len)`. The same holds for
+[`parse_copy`](parse_copy.md), [`accept`](accept.md), and [`read`](read.md).
+
 ## Examples
 
 ??? example "Example: (1) borrowed vs. owned input, and errors identical to `BasicJsonType::parse()`"

docs/mkdocs/docs/api/basic_json_document/parse_copy.md

@@ -51,6 +51,9 @@ Linear in the length of the input.
 only differs in that the input is always copied rather than sometimes borrowed. Prefer [`parse()`](parse.md) when the
 input's lifetime already covers the document's, since it avoids the copy for borrowed inputs.
 
+An integer argument that is not a `#!cpp bool` where the flags are expected, such as `#!cpp parse_copy(ptr, len)`, does not
+compile; see [`parse`](parse.md#notes).
+
 ## Examples
 
 ??? example

docs/mkdocs/docs/api/basic_json_document/read.md

@@ -54,6 +54,9 @@ page at a time, and every page costs a page fault the first time it is written.
 a 55 MB document into a reused document took about 40 % less time than parsing it into a fresh one. Programs that parse
 many documents of similar size should therefore keep one document and call `read()`.
 
+An integer argument that is not a `#!cpp bool` where the flags are expected, such as `#!cpp read(ptr, len)`, does not
+compile; see [`parse`](parse.md#notes).
+
 ## Examples
 
 ??? example

docs/mkdocs/docs/api/basic_json_document/root.md

@@ -1,10 +1,15 @@
 # <small>nlohmann::basic_json_document::</small>root
 
 ```cpp
-view_type root() const noexcept;
+// (1)
+view_type root() const& noexcept;
+
+// (2)
+view_type root() const&& = delete;
 ```
 
-Returns a view of the root value of the document.
+1. Returns a view of the root value of the document.
+2. Deleted: the view of a temporary document would dangle.
 
 ## Return value
 
@@ -21,6 +26,16 @@ Constant.
 
 ## Notes
 
+**Lifetime.** A view refers into the document, so the document must outlive it. `root()` can therefore only be called
+on a document that has a name (an lvalue); calling it on a temporary does not compile:
+
+```cpp
+auto v = json_document::parse(text).root();  // error: the document is destroyed at the end of the statement
+
+auto doc = json_document::parse(text);       // OK: keep the document alive
+auto v = doc.root();
+```
+
 `root()` is a cheap handle into the document's index, not a copy of anything; call it as often as needed. The
 returned view is valid under the same conditions as any other view of the document -- see
 [Object inspection](../basic_json_view/index.md) -- in particular, it is invalidated by the next

docs/mkdocs/docs/api/basic_json_document/set.md

@@ -23,7 +23,8 @@ has `set`; calling it on a read-only `basic_json_document` fails to compile (`#!
 
 1. Replaces the value `target` refers to with `value`.
 2. Sets the member `key` of the object `object` to `value`: assigns it if `object` already has a member with this
-   key -- the first one, should the key occur more than once, and the later duplicates are then dropped (see the
+   key -- the last one, should the key occur more than once (the member
+   [`operator[]`](../basic_json_view/operator%5B%5D.md) returns), and the other duplicates are then dropped (see the
    [Notes](#notes) below) -- or appends a new member at the end otherwise. A [null](../basic_json_view/is_null.md)
    `object` first becomes an empty object.
 3. Assigns `value` to the element at index `idx` of the array `array`, which must already exist (`#!cpp idx <
@@ -31,7 +32,10 @@ has `set`; calling it on a read-only `basic_json_document` fails to compile (`#!
 4. Sets the value the JSON pointer `ptr` refers to, relative to [`root()`](root.md), to `value`. The *parent* of the
    target must already exist: an object member is set as in 2. (added if it does not exist yet), an array element is
    assigned as in 3., and a last reference token of `#!cpp "-"`, or equal to the size of the array, appends `value`
-   instead, exactly as [`push_back`](push_back.md) would. An empty `ptr` sets [`root()`](root.md) itself, as in 1.
+   instead, exactly as [`push_back`](push_back.md) would. A [null](../basic_json_view/is_null.md) parent becomes what
+   [`basic_json::operator[]`](../basic_json/operator%5B%5D.md) with a JSON pointer makes of it: an array if the last
+   reference token is `#!cpp "-"` or consists of digits only (for an index beyond 0, the array is first filled with
+   null values up to that index), an object otherwise. An empty `ptr` sets [`root()`](root.md) itself, as in 1.
 
 In every overload, `value` is accepted three ways: a [`basic_json_view`](../basic_json_view/index.md) of *any*
 document -- read-only or editable, and it does not have to be `target`'s/`object`'s/`array`'s own document -- which
@@ -85,7 +89,8 @@ invalid argument, or `#!cpp std::bad_alloc`) leaves the document completely unch
 for the encoding that is not reclaimed. A failure of a later allocation -- while an edited array or object switches
 from its parsed layout to a growable block, see [Notes](#notes) -- can still leave a partial effect, such as a
 [null](../basic_json_view/is_null.md) `object`/`array` argument already turned into an empty object/array even
-though `value` itself was not linked in.
+though `value` itself was not linked in. Likewise, a failure of `value` in 4. leaves a null parent that is set with an
+index beyond 0 already filled with the null values before the index.
 
 ## Exceptions
 
@@ -111,8 +116,10 @@ though `value` itself was not linked in.
    [`parse_error.106`](../../home/exceptions.md#jsonexceptionparse_error106) (a leading `#!cpp '0'`),
    [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) (not a number),
    [`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) (too large for `size_type`), or
-   [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) (an empty token). Also throws what 1.
-   throws for `value`.
+   [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) (an empty token); the same errors are
+   thrown for a null parent and a token of digits (the parent is not changed then), and
+   [`out_of_range.401`](../../home/exceptions.md#jsonexceptionout_of_range401) if the index is 4294967295 or more.
+   Also throws what 1. throws for `value`.
 
 Every overload also throws [`type_error.319`](../../home/exceptions.md#jsonexceptiontype_error319) if `value` is (or
 contains) a binary value -- `BasicJsonType` can hold one, but a `json_document` cannot -- and
@@ -125,24 +132,28 @@ document") if `target`/`object`/`array` is a [discarded](../basic_json_view/is_d
 1. Linear in the size of `value` (encoding it into the document's storage): constant for a scalar, linear in the
    number of nested values for an array or object. If `target` is itself an array or object that spans more than one
    node in its parent's original, unedited layout, and `value` is a scalar, replacing it additionally costs time
-   linear in the number of elements of that parent, the *first* time -- see [Notes](#notes).
+   linear in the size of the document, the *first* time (the parent of `target` is looked up from
+   [`root()`](root.md), and then switches to links) -- see [Notes](#notes). Once the parent has links, `target` is
+   replaced in constant time: setting every element of a large array one after the other is linear overall. To avoid
+   the lookup altogether, use 3. (or 2. for an object), which know the parent.
 2. Linear in the number of members of `object`, to find an existing member with `key`, plus the complexity of 1. for
    `value`.
 3. Constant, plus the complexity of 1. for `value`.
 4. Linear in the number of reference tokens of `ptr` and, for each token, in the number of members of the object at
    that level or the index into the array (as [`at`](../basic_json_view/at.md)), plus the complexity of 2. or 3. for
-   the last token.
+   the last token; for a null parent and an index, linear in the index.
 
 ## Notes
 
 !!! info "Duplicate keys"
 
-    If `object` already has more than one member with `key` (2.), the *first* one is assigned `value` and every
-    later member with the same key is removed -- so that a lookup, an iteration, and
-    [`materialize()`](../basic_json_view/materialize.md) of `object` afterward all agree on a single value for
-    `key`, the same way [`operator[]`](../basic_json_view/operator%5B%5D.md) already picks the first occurrence of a
-    duplicate key for reading. See the [Notes on duplicate keys](../basic_json_view/operator%5B%5D.md#notes) of
-    `operator[]`.
+    If `object` already has more than one member with `key` (2.), `value` is assigned to the *last* one -- the member
+    [`operator[]`](../basic_json_view/operator%5B%5D.md), [`at`](../basic_json_view/at.md), and
+    [`find`](../basic_json_view/find.md) return for reading, so that a view taken from `object["key"]` before the call
+    shows `value` afterward -- and every other member with the same key is removed. The key stays at the
+    position of its *first* occurrence, where [`materialize()`](../basic_json_view/materialize.md) puts it as well. A
+    lookup, an iteration, and `materialize()` of `object` afterward therefore all agree on a single member for `key`. See the
+    [Notes on duplicate keys](../basic_json_view/operator%5B%5D.md#notes) of `operator[]`.
 
 Setting a member (2.) or an element (3., through 4.) of an array or object whose elements have not been edited
 before switches it from its parsed layout to a growable block holding links to its elements; a later

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

@@ -8,15 +8,18 @@ basic_json_view at(const string_t& key) const;
 
 // (2)
 basic_json_view at(size_type idx) const;
-basic_json_view at(int idx) const;
+template<typename IntegerType>
+basic_json_view at(IntegerType idx) const;
 
 // (3)
 basic_json_view at(const json_pointer& ptr) const;
 ```
 
-1. Returns the value of the object member with key `key` -- the first one, should the key occur more than once (see
+1. Returns the value of the object member with key `key` -- the last one, should the key occur more than once (see
    [Notes on duplicate keys](operator[].md#notes)).
-2. Returns the array element at index `idx`.
+2. Returns the array element at index `idx`. The template accepts every integer type except `#!cpp bool` and
+   `#!cpp std::size_t` and forwards to the `size_type` overload, as for [`operator[]`](operator[].md); a negative
+   `idx` is out of range.
 3. Returns the value a JSON pointer `ptr` refers to, starting at this value.
 
 ## Parameters
@@ -32,7 +35,7 @@ basic_json_view at(const json_pointer& ptr) const;
 
 ## Return value
 
-1. the value of the first member with key `key`
+1. the value of the last member with key `key`
 2. the element at index `idx`
 3. the value `ptr` resolves to, starting at this value
 
@@ -72,8 +75,8 @@ None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics
 ## Complexity
 
 1. Linear in the number of members: as for [`ordered_json`](../ordered_json.md), members are compared one after
-   another, in document order, stopping at the first match. Each comparison first checks the key's length --
-   already known from the index, without reading the key bytes -- before comparing its content.
+   another, in document order, scanning all of them, since the last match is wanted. Each comparison first checks the
+   key's length -- already known from the index, without reading the key bytes -- before comparing its content.
    Objects with 128 or more members get a hash index 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

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

@@ -4,8 +4,8 @@
 basic_json_view() noexcept = default;
 ```
 
-Creates an invalid (discarded) view: [`type()`](type.md) is `#!cpp value_t::discarded`,
-[`is_discarded()`](is_discarded.md) is `#!cpp true`, and `#!cpp explicit operator bool()` is `#!cpp false`.
+Creates an invalid (discarded) view: [`type()`](type.md) is `#!cpp value_t::discarded` and
+[`is_discarded()`](is_discarded.md) is `#!cpp true`.
 
 This is the only constructor a caller can use directly. Every other view is obtained from a
 [`basic_json_document`](../basic_json_document/index.md), via [`root()`](../basic_json_document/root.md) or by
@@ -44,7 +44,6 @@ placeholder for "no value yet" and later be assigned a real view.
 ## See also
 
 - [is_discarded](is_discarded.md) - return whether the view is invalid
-- [operator bool](operator_bool.md) - return whether the view refers to a value
 - [root](../basic_json_document/root.md) - the view of a document's root value
 
 ## Version history

docs/mkdocs/docs/api/basic_json_view/begin.md

@@ -24,7 +24,7 @@ Constant.
 
 For an object, iteration visits **every** member, including all occurrences of a duplicate key -- unlike
 [`operator[]`](operator[].md), [`at`](at.md), [`find`](find.md), [`contains`](contains.md), and [`count`](count.md),
-which all resolve to the *first* member with a given key. See the
+which all resolve to the *last* member with a given key. See the
 [Notes on duplicate keys](operator[].md#notes) of `operator[]`.
 
 Because objects are iterated in document order rather than sorted by key, the order seen here can differ from what

docs/mkdocs/docs/api/basic_json_view/contains.md

@@ -33,8 +33,8 @@ No-throw guarantee: this function never throws exceptions.
 ## Complexity
 
 1. Linear in the number of members: as for [`ordered_json`](../ordered_json.md), members are compared one after
-   another, in document order, stopping at the first match. Each comparison first checks the key's length -- already
-   known from the index, without reading the key bytes -- before comparing its content.
+   another, in document order, scanning all of them, since the last match is wanted. Each comparison first checks the
+   key's length -- already known from the index, without reading the key bytes -- before comparing its content.
    Objects with 128 or more members get a hash index while parsing, so that a lookup in them takes constant time
    on average.
 2. Linear in the number of reference tokens of `ptr` and, for each token, in the number of members of the object at

docs/mkdocs/docs/api/basic_json_view/count.md

@@ -23,9 +23,9 @@ No-throw guarantee: this function never throws exceptions.
 
 ## Complexity
 
-Linear in the number of members: as for [`ordered_json`](../ordered_json.md), members are compared one after
-another, in document order, stopping at the first match. Each comparison first checks the key's length -- already
-known from the index, without reading the key bytes -- before comparing its content.
+Linear in the number of members: as for [`ordered_json`](../ordered_json.md), members are compared one after another,
+in document order, scanning all of them, since the last match is wanted. Each comparison first checks the key's length
+-- already known from the index, without reading the key bytes -- before comparing its content.
 Objects with 128 or more members get a hash index while parsing, so that a lookup in them takes constant time on
 average.
 
@@ -38,7 +38,7 @@ Unlike [`BasicJsonType::count()`](../basic_json/count.md), whose return value ca
 an `ObjectType` that allows multiple entries per key, `count()` here never does: it is exactly
 [`contains()`](contains.md) as `#!cpp 0`/`#!cpp 1`. This holds even if the source text has a duplicate key -- see the
 [Notes on duplicate keys](operator[].md#notes) of `operator[]` -- because a `#!cpp count() > 1` result would require
-counting every member with a matching key, not just finding the first one.
+counting every member with a matching key (the lookup functions resolve to the *last* one).
 
 ## Examples
 

docs/mkdocs/docs/api/basic_json_view/find.md

@@ -6,7 +6,7 @@ iterator find(const char* key) const;
 iterator find(const string_t& key) const;
 ```
 
-Finds a member with key `key` -- the first one, should the key occur more than once (see
+Finds a member with key `key` -- the last one, should the key occur more than once (see
 [Notes on duplicate keys](operator[].md#notes)). If the value is not an object, or no member has this key,
 [`end()`](end.md) is returned.
 
@@ -25,9 +25,9 @@ No-throw guarantee: this function never throws exceptions.
 
 ## Complexity
 
-Linear in the number of members: as for [`ordered_json`](../ordered_json.md), members are compared one after
-another, in document order, stopping at the first match. Each comparison first checks the key's length -- already
-known from the index, without reading the key bytes -- before comparing its content.
+Linear in the number of members: as for [`ordered_json`](../ordered_json.md), members are compared one after another,
+in document order, scanning all of them, since the last match is wanted. Each comparison first checks the key's length
+-- already known from the index, without reading the key bytes -- before comparing its content.
 Objects with 128 or more members get a hash index while parsing, so that a lookup in them takes constant time on
 average.
 

docs/mkdocs/docs/api/basic_json_view/get.md

@@ -87,9 +87,9 @@ exception thrown while converting through `materialize()` (the last bullet) is d
 !!! info "Duplicate keys"
 
     `#!cpp std::map`/`#!cpp std::unordered_map` conversions keep the *last* value of a repeated key, like
-    [`materialize()`](materialize.md) and [`BasicJsonType::parse()`](../basic_json/parse.md) do. This is the opposite
-    of [`operator[]`](operator[].md)/[`at`](at.md)/[`find`](find.md)/[`contains`](contains.md), which resolve to the
-    *first* occurrence (see the [Notes on duplicate keys](operator[].md#notes)).
+    [`materialize()`](materialize.md) and [`BasicJsonType::parse()`](../basic_json/parse.md) do. This is the member
+    [`operator[]`](operator[].md)/[`at`](at.md)/[`find`](find.md)/[`contains`](contains.md) resolve to, too (see the
+    [Notes on duplicate keys](operator[].md#notes)).
 
 !!! info "No pointers, references, or implicit conversion"
 

docs/mkdocs/docs/api/basic_json_view/index.md

@@ -85,7 +85,6 @@ still refers to it -- including ones taken before the change -- reads the new va
 - [**is_primitive**](is_primitive.md) - return whether the type is primitive
 - [**is_structured**](is_structured.md) - return whether the type is structured
 - [**is_discarded**](is_discarded.md) - return whether the view is invalid
-- [**operator bool**](operator_bool.md) - return whether the view refers to a value
 
 ### Element access
 

docs/mkdocs/docs/api/basic_json_view/is_discarded.md

@@ -9,6 +9,10 @@ view (see [(constructor)](basic_json_view.md)), and for [`root()`](../basic_json
 that is itself [discarded](../basic_json_document/is_discarded.md) -- in particular, the root of a failed
 [`parse()`](../basic_json_document/parse.md) with `allow_exceptions` set to `#!cpp false`.
 
+A discarded view is also what [`operator[]`](operator[].md) returns for a missing key, an index out of range, or a
+JSON pointer that cannot be resolved, and for any access on a view that is itself discarded (so a chain such as
+`#!cpp v["a"]["b"]` is safe). [`at`](at.md) throws instead.
+
 ## Return value
 
 `#!cpp true` if the view is discarded, `#!cpp false` otherwise.
@@ -23,8 +27,9 @@ Constant.
 
 ## Notes
 
-`#!cpp v.is_discarded()` and `#!cpp !static_cast<bool>(v)` are equivalent; use whichever reads better at the call
-site.
+A `basic_json_view` is not convertible to `#!cpp bool`: such a conversion would mean "refers to a value", whereas
+`basic_json` converts to the `#!cpp bool` it holds, so the same code would silently behave differently. Test
+`#!cpp !v.is_discarded()` explicitly.
 
 ## Examples
 
@@ -45,7 +50,7 @@ site.
 
 ## See also
 
-- [operator bool](operator_bool.md) - return whether the view refers to a value
+- [operator[]](operator[].md) - access specified element; yields a discarded view where an element is missing
 - [(constructor)](basic_json_view.md) - the default constructor creates a discarded view
 - [is_discarded (basic_json_document)](../basic_json_document/is_discarded.md) - return whether the last parse failed
 - [`BasicJsonType::is_discarded`](../basic_json/is_discarded.md) - the corresponding function of `basic_json`

docs/mkdocs/docs/api/basic_json_view/items.md

@@ -48,7 +48,7 @@ Constant.
 
 As for [`begin()`](begin.md)/[`end()`](end.md), `items()` visits **every** member of an object, including all
 occurrences of a duplicate key -- unlike [`operator[]`](operator[].md), [`at`](at.md), [`find`](find.md),
-[`contains`](contains.md), and [`count`](count.md), which resolve to the *first* member with a given key. See the
+[`contains`](contains.md), and [`count`](count.md), which resolve to the *last* member with a given key. See the
 [Notes on duplicate keys](operator[].md#notes) of `operator[]`.
 
 !!! danger "Lifetime issues"
@@ -63,8 +63,8 @@ occurrences of a duplicate key -- unlike [`operator[]`](operator[].md), [`at`](a
 
     The example below shows a settings object whose source text records every update to a key as a duplicate
     member, in the order they happened. `items()` walks all of them, so the update history is visible, while
-    [`operator[]`](operator[].md) only ever sees the *first* one and [`materialize()`](materialize.md) -- like
-    [`BasicJsonType::parse()`](../basic_json/parse.md) -- keeps only the *last*.
+    [`operator[]`](operator[].md) sees the *last* one, and so does [`materialize()`](materialize.md) -- like
+    [`BasicJsonType::parse()`](../basic_json/parse.md).
 
     ```cpp
     --8<-- "examples/basic_json_view__items.cpp"

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

@@ -8,16 +8,19 @@ basic_json_view operator[](const string_t& key) const;
 
 // (2)
 basic_json_view operator[](size_type idx) const;
-basic_json_view operator[](int idx) const;
+template<typename IntegerType>
+basic_json_view operator[](IntegerType idx) const;
 
 // (3)
 basic_json_view operator[](const json_pointer& ptr) const;
 ```
 
-1. Returns the value of the object member with key `key` -- the first one, should the key occur more than once (see
+1. Returns the value of the object member with key `key` -- the last one, should the key occur more than once (see
    the [Notes](#notes) below) -- or a [discarded](is_discarded.md) view if there is no such member.
-2. Returns the array element at index `idx`, or a [discarded](is_discarded.md) view if `idx` is out of range. (The
-   `#!cpp int` overload only exists so that an integer literal is not ambiguous between this overload and 1.)
+2. Returns the array element at index `idx`, or a [discarded](is_discarded.md) view if `idx` is out of range. The
+   template accepts every integer type except `#!cpp bool` and `#!cpp std::size_t` (`#!cpp int`, `#!cpp unsigned`,
+   `#!cpp long`, `#!cpp std::int64_t`, ...) and forwards to the `size_type` overload, so that an integer argument is
+   not ambiguous between that overload and 1; a negative `idx` is out of range.
 3. Returns the value a JSON pointer `ptr` refers to, starting at this value, or a [discarded](is_discarded.md) view
    wherever resolving it further is not possible without inserting into or extending the document (see
    [Return value](#return-value) and [Exceptions](#exceptions) below).
@@ -35,10 +38,12 @@ basic_json_view operator[](const json_pointer& ptr) const;
 
 ## Return value
 
-1. the value of the first member with key `key`, or a discarded view if `#!cpp is_object()` is `#!cpp false` or no
-   member has this key
-2. the element at index `idx`, or a discarded view if `#!cpp is_array()` is `#!cpp false` or `#!cpp idx >= size()`
-3. the value `ptr` resolves to, starting at this value, or a discarded view for exactly the reference tokens where the
+1. the value of the last member with key `key`, or a discarded view if no member has this key (or if this view is
+   [discarded](is_discarded.md))
+2. the element at index `idx`, or a discarded view if `#!cpp idx >= size()` or `idx` is negative (or if this view is
+   [discarded](is_discarded.md))
+3. the value `ptr` resolves to, starting at this value, or a discarded view (also if this view is
+   [discarded](is_discarded.md)) for exactly the reference tokens where the
    **const** overload of [`BasicJsonType::operator[]`](../basic_json/operator%5B%5D.md) invokes undefined behavior for
    the same pointer and the same document: an object member that does not exist, or an array index that is out of
    range
@@ -49,10 +54,12 @@ Strong exception safety: if an exception is thrown, there are no changes to the
 
 ## Exceptions
 
-1. Throws [`type_error.305`](../../home/exceptions.md#jsonexceptiontype_error305) if the value is not an object --
+1. Throws [`type_error.305`](../../home/exceptions.md#jsonexceptiontype_error305) if the value is not an object and
+   not [discarded](is_discarded.md) --
    the same exception, with the same message, that the **const** overload of
    [`BasicJsonType::operator[]`](../basic_json/operator%5B%5D.md) throws for a string argument on a non-object value.
-2. Throws [`type_error.305`](../../home/exceptions.md#jsonexceptiontype_error305) if the value is not an array --
+2. Throws [`type_error.305`](../../home/exceptions.md#jsonexceptiontype_error305) if the value is not an array and
+   not [discarded](is_discarded.md) --
    the same exception, with the same message, that the **const** overload of
    [`BasicJsonType::operator[]`](../basic_json/operator%5B%5D.md) throws for a numeric argument on a non-array value.
 3. Throws the same exceptions, with the same messages, that the **const** overload of
@@ -73,9 +80,9 @@ None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics
 ## Complexity
 
 1. Linear in the number of members: as for [`ordered_json`](../ordered_json.md), members are compared one after
-   another, in document order, stopping at the first match. Each comparison first checks the key's length --
-   already known from the index, without reading the key bytes -- before comparing its content, so a key of a
-   different length than `key` is rejected without touching the source text.
+   another, in document order, scanning all of them, since the last match is wanted. Each comparison first checks the
+   key's length -- already known from the index, without reading the key bytes -- before comparing its content, so a
+   key of a different length than `key` is rejected without touching the source text.
    Objects with 128 or more members get a hash index 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
@@ -86,20 +93,30 @@ None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics
 ## Notes
 
 Unlike `BasicJsonType::operator[]`, which is undefined behavior (guarded by a
-[runtime assertion](../../features/assertions.md)) for a missing key on a **const** value, this operator always
-returns a safe, testable result: a [discarded](is_discarded.md) view, which is `#!cpp false` in a boolean context.
+[runtime assertion](../../features/assertions.md)) for a missing key on a **const** value, this operator returns a
+safe, testable result for a missing key or an index out of range: a [discarded](is_discarded.md) view, which is
+tested with [`is_discarded`](is_discarded.md).
 There is also no non-const overload that inserts a missing key or extends an array -- a view never modifies the
 document.
 
+!!! info "Chained access"
+
+    `#!cpp operator[]` on a [discarded](is_discarded.md) view returns a discarded view and does not throw, so a chain
+    like `#!cpp v["a"]["b"][0]` is safe even if `"a"` or `"b"` is missing: the first missing step makes the whole
+    result discarded, which is tested once at the end. Type errors on values that are *not* discarded still throw: a
+    key on an array or a primitive, or an index on an object or a primitive, is `type_error.305` as for
+    `BasicJsonType`. [`at`](at.md) still throws for a discarded view, as it does for a missing key.
+
 !!! info "Duplicate keys"
 
     If the source text has an object with a duplicate key, `#!cpp operator[]` (and [`at`](at.md), [`find`](find.md),
-    [`contains`](contains.md), [`count`](count.md)) all resolve to the *first* member with that key, because a
-    lookup can stop as soon as it finds a match. This is different from
-    [`materialize()`](materialize.md) (and [`BasicJsonType::parse()`](../basic_json/parse.md)), which replay every
-    member in order and so end up keeping the *last* value for a repeated key -- there is no reason for them to stop
-    early. [`begin()`](begin.md)/[`end()`](end.md) and [`items()`](items.md) iterate over *all* members, including
-    duplicates, in document order. See the example below and [`size()`](size.md#notes).
+    [`contains`](contains.md), [`count`](count.md), [`value`](value.md), and JSON pointer resolution) all resolve to
+    the *last* member with that key. This is the member [`materialize()`](materialize.md) (and
+    [`BasicJsonType::parse()`](../basic_json/parse.md)) keeps, so a lookup in the view and in the materialized value
+    agree. [`begin()`](begin.md)/[`end()`](end.md) and [`items()`](items.md) iterate over *all* members, including
+    duplicates, in document order. A lookup in an object without a hash index scans all members for this: it cannot
+    stop at the first match. The hash index of a larger object (128 members or more) leads to the last member of a key
+    as well. See the example below and [`size()`](size.md#notes).
 
 !!! info "JSON pointer resolution"
 

docs/mkdocs/docs/api/basic_json_view/operator_bool.md

@@ -1,46 +0,0 @@
-# <small>nlohmann::basic_json_view::</small>operator bool
-
-```cpp
-explicit operator bool() const noexcept;
-```
-
-Returns whether this view refers to a value, i.e. the negation of [`is_discarded()`](is_discarded.md). Being
-`#!cpp explicit`, this conversion is only considered in a boolean context (`#!cpp if (v)`, `#!cpp !v`, `#!cpp v &&
-...`), not for implicit conversions to other types.
-
-## Return value
-
-`#!cpp true` if the view refers to a value, `#!cpp false` if it is [discarded](is_discarded.md).
-
-## Exception safety
-
-No-throw guarantee: this function never throws exceptions.
-
-## Complexity
-
-Constant.
-
-## Examples
-
-??? example
-
-    The example below classifies several parsed documents by the type of their root value, without materializing any
-    of them into a `BasicJsonType` value.
-
-    ```cpp
-    --8<-- "examples/basic_json_view__type_predicates.cpp"
-    ```
-
-    Output:
-
-    ```json
-    --8<-- "examples/basic_json_view__type_predicates.output"
-    ```
-
-## See also
-
-- [is_discarded](is_discarded.md) - return whether the view is invalid
-
-## Version history
-
-- Added in version 3.13.0.

docs/mkdocs/docs/api/basic_json_view/value.md

@@ -12,7 +12,7 @@ T value(const json_pointer& ptr, const T& default_value) const;
 string_t value(const json_pointer& ptr, const char* default_value) const;
 ```
 
-1. Returns the value of the object member with key `key` -- the first one, should the key occur more than once (see
+1. Returns the value of the object member with key `key` -- the last one, should the key occur more than once (see
    [Notes on duplicate keys](operator[].md#notes)) -- converted to `T`, or `default_value` if there is no such member.
 2. Returns the value a JSON pointer `ptr` refers to, starting at this value, converted to `T`, or `default_value` if
    `ptr` cannot be resolved.
@@ -39,7 +39,7 @@ equivalent) deduce `string_t`, not `const char*`, for their return type and for
 
 ## Return value
 
-1. the first member with key `key`, converted to `T`, or `default_value`
+1. the last member with key `key`, converted to `T`, or `default_value`
 2. the value `ptr` resolves to, converted to `T`, or `default_value`
 
 ## Exception safety
@@ -68,8 +68,8 @@ None of these exceptions carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics
 ## Complexity
 
 1. Linear in the number of members: as for [`operator[]`](operator[].md#complexity), members are compared one after
-   another, in document order, stopping at the first match. Plus the complexity of converting the found member to
-   `T` (see [`get`](get.md)).
+   another, in document order, scanning all of them, since the last match is wanted. Plus the complexity of converting
+   the found member to `T` (see [`get`](get.md)).
    Objects with 128 or more members get a hash index while parsing, so that a lookup in them takes constant time
    on average.
 2. Linear in the number of reference tokens of `ptr` and, for each token, in the number of members of the object at

docs/mkdocs/docs/examples/basic_json_view__basic_json_view.cpp

@@ -8,10 +8,10 @@ int main()
     // the default constructor is the only public one: it creates an invalid
     // (discarded) view, useful as a "no value yet" placeholder
     nlohmann::json_view v;
-    std::cout << static_cast<bool>(v) << ' ' << v.is_discarded() << '\n';
+    std::cout << v.is_discarded() << '\n';
 
     // views are trivially copyable handles (two pointers); the document owns
     // the actual data
     nlohmann::json_view copy = v;
-    std::cout << static_cast<bool>(copy) << '\n';
+    std::cout << copy.is_discarded() << '\n';
 }

docs/mkdocs/docs/examples/basic_json_view__basic_json_view.output

@@ -1,2 +1,2 @@
-false true
-false
+true
+true

docs/mkdocs/docs/examples/basic_json_view__items.cpp

@@ -7,8 +7,8 @@ int main()
 {
     // a settings object whose source text records every update to a key as
     // a duplicate member. items() visits all of them, in document order, so
-    // the update history is visible; operator[] only ever sees the first
-    // one, and materialize() -- like basic_json::parse() -- keeps the last
+    // the update history is visible; operator[] and materialize() -- like
+    // basic_json::parse() -- see the last one
     json_document updates = json_document::parse(R"({"retries": 1, "timeout": 30, "retries": 5})");
     const auto settings = updates.root();
 
@@ -17,6 +17,6 @@ int main()
         std::cout << item.key() << '=' << item.value().materialize().dump() << '\n';
     }
 
-    std::cout << "first \"retries\" seen by operator[]: " << settings["retries"].materialize().dump() << '\n';
+    std::cout << "last \"retries\" seen by operator[]: " << settings["retries"].materialize().dump() << '\n';
     std::cout << "last \"retries\" kept by materialize(): " << settings.materialize()["retries"].dump() << '\n';
 }

docs/mkdocs/docs/examples/basic_json_view__items.output

@@ -1,5 +1,5 @@
 retries=1
 timeout=30
 retries=5
-first "retries" seen by operator[]: 1
+last "retries" seen by operator[]: 5
 last "retries" kept by materialize(): 5

docs/mkdocs/docs/examples/basic_json_view__operator[].cpp

@@ -22,17 +22,19 @@ int main()
         std::cout << user["name"].materialize().dump();
 
         // operator[] on a missing object key gives a discarded view -- test
-        // it with a plain "if". The const overload of json::operator[]
+        // it with is_discarded(). The const overload of json::operator[]
         // would instead be undefined behavior (guarded by an assertion) for
         // a missing key
-        if (const auto email = user["email"])
+        const auto email = user["email"];
+        if (!email.is_discarded())
         {
             std::cout << " <" << email.materialize().dump() << ">";
         }
 
         // the same holds for an array index past the end: a discarded view,
         // not undefined behavior
-        if (const auto first_tag = user["tags"][0])
+        const auto first_tag = user["tags"][0];
+        if (!first_tag.is_discarded())
         {
             std::cout << " #" << first_tag.materialize().dump();
         }

docs/mkdocs/docs/examples/basic_json_view__operator[]_json_pointer.cpp

@@ -25,7 +25,8 @@ int main()
     // a missing key or an out-of-range index along the path gives a
     // discarded view, exactly where const json::operator[] would be
     // undefined behavior for the same pointer
-    if (const auto missing = root[json_pointer("/region/servers/5/metrics/cpu")])
+    const auto missing = root[json_pointer("/region/servers/5/metrics/cpu")];
+    if (!missing.is_discarded())
     {
         std::cout << missing.materialize().dump() << '\n';
     }

docs/mkdocs/docs/examples/basic_json_view__type_predicates.cpp

@@ -35,8 +35,8 @@ int main()
     // parse without exceptions, are both discarded
     nlohmann::json_view invalid;
     json_document failed = json_document::parse("not json", /* allow_exceptions */ false);
-    std::cout << static_cast<bool>(invalid) << ' ' << invalid.is_discarded() << '\n';
-    std::cout << static_cast<bool>(failed.root()) << ' ' << failed.root().is_discarded() << '\n';
+    std::cout << invalid.is_discarded() << '\n';
+    std::cout << failed.root().is_discarded() << '\n';
 
     // type() returns the same value_t enumeration as basic_json::type()
     std::cout << (d_object.root().type() == nlohmann::json::value_t::object) << '\n';

docs/mkdocs/docs/examples/basic_json_view__type_predicates.output

@@ -7,6 +7,6 @@ true
 true true
 true false
 false
-false true
-false true
+true
+true
 true

docs/mkdocs/docs/features/json_view.md

@@ -81,6 +81,9 @@ Moving the document itself is fine and does **not** invalidate its views: the in
 that keeps its address across the move. Take a fresh view from [`root()`](../api/basic_json_document/root.md)
 whenever any of the other conditions above was not met.
 
+Because a view dies with its document, [`root()`](../api/basic_json_document/root.md) is not callable on a temporary
+document: `#!cpp auto v = json_document::parse(text).root();` does not compile. Give the document a name first.
+
 ??? example "Example: borrowed and owned documents, and when views become invalid"
 
     ```cpp
@@ -113,7 +116,7 @@ whenever any of the other conditions above was not met.
 
 - **Only 64-bit integers.** `basic_json_document<BasicJsonType>` requires `BasicJsonType::number_integer_t` and
   `number_unsigned_t` to both be 64 bits wide; this is a compile-time `#!cpp static_assert`.
-- **A 4 GiB input limit.** An input of 4 GiB or more throws
+- **A 4 GiB input limit.** An input of 4294967280 bytes (4 GiB minus 16 bytes) or more throws
   [`out_of_range.416`](../home/exceptions.md#jsonexceptionout_of_range416), a limit
   `#!cpp basic_json::parse()` does not have.
 - **A stream is always read to its end.** There is no partial/streaming read of an `#!cpp std::istream`.
@@ -126,14 +129,21 @@ whenever any of the other conditions above was not met.
   members in the order they appear in the source text. `basic_json`'s default `object_t` is a `std::map`, which
   sorts by key, so iterating a [`materialize()`](../api/basic_json_view/materialize.md)d value can print members in
   a different order than iterating the view they came from.
+- **Chained access is safe.** [`operator[]`](../api/basic_json_view/operator%5B%5D.md) with a missing key, an index
+  out of range, or an unresolvable JSON pointer returns a [discarded](../api/basic_json_view/is_discarded.md) view, and
+  `operator[]` on a discarded view returns a discarded view without throwing: `#!cpp v["a"]["b"][0]` can be tested
+  once at the end. Type errors on values that exist (a key on an array, an index on an object) still throw, and
+  [`at`](../api/basic_json_view/at.md) throws for every missing value.
 - **Duplicate keys are visible.** If an object in the source text repeats a key,
   [`begin()`](../api/basic_json_view/begin.md)/[`end()`](../api/basic_json_view/end.md) and
   [`items()`](../api/basic_json_view/items.md) visit *every* occurrence (and [`size()`](../api/basic_json_view/size.md)
   counts all of them), while [`operator[]`](../api/basic_json_view/operator%5B%5D.md),
   [`at`](../api/basic_json_view/at.md), [`find`](../api/basic_json_view/find.md),
   [`contains`](../api/basic_json_view/contains.md), and [`count`](../api/basic_json_view/count.md) resolve to the
-  *first* occurrence, since a lookup can stop as soon as it finds a match. `basic_json::parse()` (and so
-  [`materialize()`](../api/basic_json_view/materialize.md)) instead keeps only the *last* value for a repeated key.
+  *last* occurrence -- the one `basic_json::parse()` (and so
+  [`materialize()`](../api/basic_json_view/materialize.md)) keeps for a repeated key -- which makes a lookup scan all
+  members instead of stopping at a match (objects with 128 members or more get a hash index that leads to the last
+  occurrence directly).
   See the [Notes on duplicate keys](../api/basic_json_view/operator%5B%5D.md#notes) of `operator[]`.
 - **No [`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md) path.** Exceptions thrown by `basic_json_view`'s own
   element access and lookup functions never carry the JSON Pointer path `JSON_DIAGNOSTICS` would otherwise add: the

docs/mkdocs/docs/features/types/template_parameters.md

@@ -353,16 +353,21 @@ using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;
 ### Always required
 
 - A member type `value_type` that is one byte wide and `char`-compatible. The library stores and processes UTF-8
-  encoded `char` data and passes `data()` to functions that take a `#!cpp const char*`, such as `#!cpp std::strtod`.
+  encoded `char` data and passes `data()` to functions that take a `#!cpp const char*`, such as `#!cpp std::strtold`
+  (only used to parse a `#!cpp long double` that is not IEEE 754 binary64, see
+  [`NumberFloatType`](#numberfloattype)).
   `#!cpp std::wstring`, `#!cpp std::u16string`, and `#!cpp std::u32string` are **not** valid choices; see the FAQ on
   [wide string handling](../../home/faq.md#wide-string-handling).
 - Constructors: default, copy, move, from `#!cpp const char*` (which must not be `#!cpp explicit`), from
   `#!cpp (const char*, size_type)`, and from `#!cpp (size_type, char)`; and copy or move assignment.
 - Member functions `size()`, `clear()`, `resize(n, c)`, `data()`, `push_back(char)`, and `operator[]`
   (const and non-const, returning references). `c_str()` and `back()` are **not** required.
-- `data()` must return a pointer to a contiguous, **null-terminated** buffer -- the parser may hand it to
-  `#!cpp std::strtod`, which reads up to the null character. A type whose `data()` is not null-terminated does not
-  fail to compile; it can silently misparse floating-point numbers.
+- `data()` must return a pointer to a contiguous, **null-terminated** buffer. `#!cpp float`, `#!cpp double`, and a
+  `#!cpp long double` that is IEEE 754 binary64 are converted by the library itself and do not depend on this. For any
+  other `NumberFloatType` (a `#!cpp long double` of another format), the parser falls back to `#!cpp std::strtold` when
+  `#!cpp std::from_chars` is not available or declines the token, and `std::strtold` reads up to the null character. A type whose `data()`
+  is not null-terminated does not fail to compile; with such a `NumberFloatType` it can silently misparse
+  floating-point numbers.
 - `append(const char*, size_type)`, used by [`dump`](../../api/basic_json/dump.md), and `append(const StringType&)`,
   used by the CBOR reader for indefinite-length strings. The library's internal string concatenation additionally has
   to append a `#!cpp char` and a `#!cpp const char*`; for each it selects between `append(arg)`, `#!cpp operator+=`,

docs/mkdocs/docs/home/architecture.md

@@ -210,12 +210,13 @@ packet-beta
 - **Navigation** needs no pointers: the elements of an array or object follow its node, and the node after a value's
   subtree is `next` nodes further for an array or object, and the next node otherwise (`document_data::after`). Views
   step from element to element this way and skip whole subtrees in constant time.
-- **Offsets** are 32 bits wide, so a document is limited to 4 GiB (`out_of_range.416`).
+- **Offsets** are 32 bits wide, so a document is limited to 4294967279 bytes, 4 GiB minus 16 bytes (a margin below
+  2^32 for positions one scanner step past the end of the text; `out_of_range.416`).
 - **Large objects** (128 members or more) get a hash index after parsing
   ([`detail/view/object_index.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/view/object_index.hpp)):
   an open-addressing table whose slots hold the distance from the object's node to a key's node, so that a lookup does
-  not compare every key. The object's `extra` holds the number of its table. Only 65,535 tables fit into `extra`;
-  objects beyond them are searched linearly.
+  not compare every key. Of duplicate keys the table leads to the last, as a linear search does. The object's `extra`
+  holds the number of its table. Only 65,535 tables fit into `extra`; objects beyond them are searched linearly.
 
 For example, `#!json {"a": [1, 2.5]}` becomes five nodes. Each node's elements follow it, and `next` leads from an
 array or object past its subtree:

docs/mkdocs/docs/home/exceptions.md

@@ -824,8 +824,9 @@ does not list an enumerator and it is therefore converted like the first listed
 
 ### json.exception.type_error.319
 
-[`basic_json_document::set`](../api/basic_json_document/set.md) and
-[`basic_json_document::push_back`](../api/basic_json_document/push_back.md) can store any `basic_json` value except
+[`basic_json_document::set`](../api/basic_json_document/set.md),
+[`basic_json_document::push_back`](../api/basic_json_document/push_back.md), and
+[`basic_json_document::insert`](../api/basic_json_document/insert.md) can store any `basic_json` value except
 a binary one: a `json_document` has no representation for [binary values](../features/binary_values.md), which only
 ever arise from parsing a binary format or from an explicit [`json::binary`](../api/basic_json/binary.md) value, not
 from JSON text.
@@ -1103,7 +1104,7 @@ MessagePack's ext type and BSON's binary subtype are each stored in a single byt
 
 [`basic_json_document::parse()`](../api/basic_json_document/parse.md) and the other parsing functions of
 [`basic_json_document`](../api/basic_json_document/index.md) index a value's position in the source text in 32 bits,
-so they do not support an input of 4 GiB or more. The same 32-bit limit applies to an **editable** document's own
+so they do not support an input of 4294967280 bytes (4 GiB minus 16 bytes) or more. The same 32-bit limit applies to an **editable** document's own
 storage: [`set`](../api/basic_json_document/set.md) and [`push_back`](../api/basic_json_document/push_back.md) throw
 this exception once the strings and number tokens written by edits reach 4 GiB in total, or once more than
 4294967295 arrays/objects have had an element set or appended to them. The same limit applies to an
@@ -1113,7 +1114,7 @@ count, the text, or the decoded strings it would write would individually reach
 !!! failure "Example messages"
 
     ```
-    [json.exception.out_of_range.416] input of 4 GiB or more is not supported by json_document
+    [json.exception.out_of_range.416] input of 4294967280 bytes or more is not supported by json_document
     ```
     ```
     [json.exception.out_of_range.416] edits of 4 GiB or more are not supported by json_document

docs/mkdocs/docs/home/license.md

@@ -18,7 +18,7 @@ The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed und
 
 The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright © 2009 [Florian Loitsch](https://florian.loitsch.com/)
 
-The class contains a port of the shortest double-to-decimal conversion of [Żmij](https://github.com/vitaut/zmij) by Victor Zverovich, which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright © 2025 [Victor Zverovich](https://github.com/vitaut)
+The class contains a port of the shortest double-to-decimal conversion of [Żmij](https://github.com/vitaut/zmij) by Victor Zverovich, including the conversion of the digits to text by Xiang JunBo and the SIMD instruction sequence of Dougall Johnson, which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright © 2025 [Victor Zverovich](https://github.com/vitaut)
 
 The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).
 

docs/mkdocs/mkdocs.yml

@@ -289,7 +289,6 @@ nav:
           - 'materialize': api/basic_json_view/materialize.md
           - 'number_format': api/basic_json_view/number_format.md
           - 'number_token': api/basic_json_view/number_token.md
-          - 'operator bool': api/basic_json_view/operator_bool.md
           - 'operator<<': api/basic_json_view/operator_ltlt.md
           - 'operator[]': api/basic_json_view/operator[].md
           - 'operator==': api/basic_json_view/operator_eq.md

include/nlohmann/detail/abi_config.hpp

@@ -15,10 +15,11 @@ namespace detail
 {
 
 /*!
-@brief the configuration macros that change the library's behavior
+@brief the configuration macros that json_view.hpp reads
 
 json.hpp undefines these macros at its end (see macro_unscope.hpp), so code
-that builds on the library after it (json_view.hpp) reads them here. Like the
+that builds on the library after it (json_view.hpp) reads them here. A macro
+is added when the view starts to depend on it. Like the
 macros, they are part of the ABI namespace, so they always match the
 basic_json they are used with.
 */
@@ -26,8 +27,6 @@ struct abi_config
 {
     /// JSON_STRICT_NUL_HANDLING: a null byte is an error, not the end of input
     static constexpr bool strict_nul_handling = JSON_STRICT_NUL_HANDLING != 0;
-    /// JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
-    static constexpr bool legacy_discarded_value_comparison = JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON != 0;
 };
 
 }  // namespace detail

include/nlohmann/detail/bit_ops.hpp

@@ -9,8 +9,9 @@
 #pragma once
 
 #include <cstdint> // uint64_t
-#if !defined(__SIZEOF_INT128__) && defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
-    #include <intrin0.h> // __umulh, _umul128
+#include <cstring> // memcpy
+#if defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64)) && (!defined(__SIZEOF_INT128__) || (!defined(__GNUC__) && !defined(__clang__)))
+    #include <intrin0.h> // __umulh, _umul128, _BitScanForward64, _BitScanReverse64
 #endif
 
 #include <nlohmann/detail/macro_scope.hpp> // JSON_HEDLEY_ALWAYS_INLINE, NLOHMANN_JSON_NAMESPACE_BEGIN
@@ -28,6 +29,10 @@ inline int count_leading_zeros(std::uint64_t x) noexcept
 {
 #if defined(__GNUC__) || defined(__clang__)
     return __builtin_clzll(x);
+#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
+    unsigned long index = 0;
+    _BitScanReverse64(&index, x);
+    return 63 - static_cast<int>(index);
 #else
     int n = 0;
     for (int shift = 32; shift != 0; shift >>= 1)
@@ -47,6 +52,10 @@ inline int count_trailing_zeros(std::uint64_t x) noexcept
 {
 #if defined(__GNUC__) || defined(__clang__)
     return __builtin_ctzll(x);
+#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
+    unsigned long index = 0;
+    _BitScanForward64(&index, x);
+    return static_cast<int>(index);
 #else
     int n = 0;
     for (int shift = 32; shift != 0; shift >>= 1)
@@ -94,15 +103,21 @@ inline uint128_parts full_multiplication(std::uint64_t a, std::uint64_t b) noexc
 #endif
 }
 
-/// eight bytes as a little-endian word (compilers fold this into one load on
-/// little-endian targets; always inlined, as GCC otherwise calls it in the
-/// number loops)
+/// eight bytes as a little-endian word (a single load on little-endian
+/// targets; always inlined, as GCC otherwise calls it in the number loops)
 JSON_HEDLEY_ALWAYS_INLINE std::uint64_t read_eight_bytes(const unsigned char* b) noexcept
 {
+#if defined(_MSC_VER) || defined(__x86_64__) || defined(__i386__) || (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
+    // the byte order already matches (all MSVC targets are little-endian)
+    std::uint64_t result = 0;
+    std::memcpy(&result, b, sizeof(result));
+    return result;
+#else
     return static_cast<std::uint64_t>(b[0]) | (static_cast<std::uint64_t>(b[1]) << 8u)
            | (static_cast<std::uint64_t>(b[2]) << 16u) | (static_cast<std::uint64_t>(b[3]) << 24u)
            | (static_cast<std::uint64_t>(b[4]) << 32u) | (static_cast<std::uint64_t>(b[5]) << 40u)
            | (static_cast<std::uint64_t>(b[6]) << 48u) | (static_cast<std::uint64_t>(b[7]) << 56u);
+#endif
 }
 
 /// eight bytes as a little-endian word

include/nlohmann/detail/conversions/to_chars.hpp

@@ -4,6 +4,7 @@
 // |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 //
 // SPDX-FileCopyrightText: 2009 Florian Loitsch <https://florian.loitsch.com/>
+// SPDX-FileCopyrightText: 2025 Victor Zverovich <https://github.com/vitaut/zmij>
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT
 
@@ -939,88 +940,6 @@ void grisu2(char* buf, int& len, int& decimal_exponent, FloatType value)
     grisu2(buf, len, decimal_exponent, w.minus, w.w, w.plus);
 }
 
-/*!
-@brief the shortest digits of a positive finite float (other than double): Grisu2
-*/
-template<typename FloatType>
-JSON_HEDLEY_NON_NULL(1)
-void shortest_digits(char* buf, int& len, int& decimal_exponent, FloatType value)
-{
-    grisu2(buf, len, decimal_exponent, value);
-}
-
-/*!
-@brief the shortest digits of a positive finite double: the conversion of
-Zmij (see zmij.hpp), which always finds the shortest digits that read back as
-the same value (Grisu2 does not for about one double in a thousand), and the
-closest of them if there are several
-
-v = buf * 10^decimal_exponent, as for grisu2()
-*/
-JSON_HEDLEY_NON_NULL(1)
-inline void shortest_digits(char* buf, int& len, int& decimal_exponent, double value)
-{
-    static_assert(std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53,
-                  "internal error: the conversion of Zmij needs IEEE 754 binary64 doubles");
-    JSON_ASSERT(std::isfinite(value));
-    JSON_ASSERT(value > 0);
-
-    std::uint64_t bits = 0;
-    std::memcpy(&bits, &value, sizeof(bits));
-    zmij::decimal d = zmij::to_decimal(bits);
-    // without trailing zeros (up to 16): 8, 4, 2, 1 at a time
-    while (d.significand % 100000000 == 0)
-    {
-        d.significand /= 100000000;
-        d.exponent += 8;
-    }
-    if (d.significand % 10000 == 0)
-    {
-        d.significand /= 10000;
-        d.exponent += 4;
-    }
-    if (d.significand % 100 == 0)
-    {
-        d.significand /= 100;
-        d.exponent += 2;
-    }
-    if (d.significand % 10 == 0)
-    {
-        d.significand /= 10;
-        d.exponent += 1;
-    }
-    // at most 17 digits, written from the back two at a time
-    static constexpr const char* pairs =
-        "00010203040506070809101112131415161718192021222324252627282930313233343536373839"
-        "40414243444546474849505152535455565758596061626364656667686970717273747576777879"
-        "8081828384858687888990919293949596979899";
-    std::array<char, 20> digits{};
-    std::size_t n = digits.size();
-    while (d.significand >= 100)
-    {
-        const std::uint64_t two_digits = d.significand % 100; // a variable: GCC calls a cast of the remainder useless where std::uint64_t is std::size_t
-        const auto i = static_cast<std::size_t>(two_digits) * 2;
-        d.significand /= 100;
-        n -= 2;
-        digits[n] = pairs[i];
-        digits[n + 1] = pairs[i + 1];
-    }
-    if (d.significand >= 10)
-    {
-        const auto i = static_cast<std::size_t>(d.significand) * 2;
-        n -= 2;
-        digits[n] = pairs[i];
-        digits[n + 1] = pairs[i + 1];
-    }
-    else
-    {
-        digits[--n] = static_cast<char>('0' + d.significand);
-    }
-    len = static_cast<int>(digits.size() - n);
-    std::memcpy(buf, digits.data() + n, static_cast<std::size_t>(len));
-    decimal_exponent = d.exponent;
-}
-
 /*!
 @brief appends a decimal representation of e to buf
 @return a pointer to the element following the exponent.
@@ -1465,11 +1384,30 @@ inline char* write_short_decimal(char* first, std::uint64_t digits, int exp) noe
     return write_short_decimal(first, digits, count, exp);
 }
 
-/// a positive finite float (other than double): Grisu2 and format_buffer()
+/*!
+@brief whether FloatType is an IEEE 754 binary64 type (a double, or a long double
+that has the same format, as with MSVC and on Apple's Arm CPUs)
+
+These are the types the conversion of Zmij (see zmij.hpp) is used for; all
+others (binary32, or a format the library does not know) use Grisu2.
+*/
+template<typename FloatType>
+constexpr bool has_binary64_format() noexcept
+{
+    return std::numeric_limits<FloatType>::is_iec559
+           && std::numeric_limits<FloatType>::digits == 53
+           && std::numeric_limits<FloatType>::max_exponent == 1024
+           && sizeof(FloatType) == sizeof(std::uint64_t);
+}
+
+template<typename FloatType>
+struct is_binary64 : std::integral_constant<bool, has_binary64_format<FloatType>()> {};
+
+/// a positive finite float (other than binary64): Grisu2 and format_buffer()
 template<typename FloatType>
 JSON_HEDLEY_NON_NULL(1, 2)
 JSON_HEDLEY_RETURNS_NON_NULL
-char* write_positive(char* first, const char* last, FloatType value)
+char* write_positive_grisu2(char* first, const char* last, FloatType value)
 {
     JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10);
     static_cast<void>(last); // (only used in the assertion)
@@ -1480,7 +1418,7 @@ char* write_positive(char* first, const char* last, FloatType value)
     // len is the length of the buffer, i.e., the number of decimal digits.
     int len = 0;
     int decimal_exponent = 0;
-    shortest_digits(first, len, decimal_exponent, value);
+    grisu2(first, len, decimal_exponent, value);
 
     JSON_ASSERT(len <= std::numeric_limits<FloatType>::max_digits10);
 
@@ -1496,15 +1434,16 @@ char* write_positive(char* first, const char* last, FloatType value)
     return format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
 }
 
-/// a positive finite double: the shortest digits (Zmij), laid out by
+/// a positive finite binary64 number: the shortest digits (Zmij), laid out by
 /// write_shortest() (through a local buffer if [first, last) is shorter than
 /// the 41 bytes it may write)
+template<typename FloatType>
 JSON_HEDLEY_NON_NULL(1, 2)
 JSON_HEDLEY_RETURNS_NON_NULL
-inline char* write_positive(char* first, const char* last, double value)
+char* write_positive_zmij(char* first, const char* last, FloatType value)
 {
-    static_assert(std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53,
-                  "internal error: the conversion of Zmij needs IEEE 754 binary64 doubles");
+    static_assert(is_binary64<FloatType>::value,
+                  "internal error: the conversion of Zmij needs IEEE 754 binary64 numbers");
     std::uint64_t bits = 0;
     std::memcpy(&bits, &value, sizeof(bits));
     const zmij::shortest_decimal d = zmij::to_shortest(bits);
@@ -1519,6 +1458,34 @@ inline char* write_positive(char* first, const char* last, double value)
     return first + len;
 }
 
+/// a positive finite binary64 number: Zmij (as a long double has the format of
+/// a double here, its bits are those of the double of the same value)
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
+char* write_positive(char* first, const char* last, FloatType value, std::true_type /*is_binary64*/)
+{
+    return write_positive_zmij(first, last, value);
+}
+
+/// a positive finite float of any other format: Grisu2
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
+char* write_positive(char* first, const char* last, FloatType value, std::false_type /*is_binary64*/)
+{
+    return write_positive_grisu2(first, last, value);
+}
+
+/// a positive finite float: Zmij for binary64 numbers, Grisu2 otherwise
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
+char* write_positive(char* first, const char* last, FloatType value)
+{
+    return write_positive(first, last, value, is_binary64<FloatType> {});
+}
+
 }  // namespace dtoa_impl
 
 /*!

include/nlohmann/detail/conversions/zmij.hpp

@@ -36,13 +36,6 @@ computed from the compressed tables of Zmij beyond it.
 namespace zmij
 {
 
-/// significand * 10^exponent
-struct decimal
-{
-    std::uint64_t significand;
-    int exponent;
-};
-
 /// the compressed powers of ten of Zmij
 inline const std::array<std::uint64_t, 28>& pow10_minor() noexcept
 {
@@ -221,18 +214,6 @@ JSON_HEDLEY_ALWAYS_INLINE shortest_decimal to_shortest(std::uint64_t bits) noexc
     return shortest_decimal{integral, dec_exp, static_cast<unsigned char>(digit), !round_up && !round_down};
 }
 
-/// The shortest decimal in the rounding interval of a positive finite double
-/// given by its bits, as one number. The significand can end in zeros.
-inline decimal to_decimal(std::uint64_t bits) noexcept
-{
-    const shortest_decimal d = to_shortest(bits);
-    if (d.has_digit)
-    {
-        return decimal{(d.integral * 10) + d.digit, d.exponent};
-    }
-    return decimal{d.integral, d.exponent + 1};
-}
-
 }  // namespace zmij
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/view/builder.hpp

@@ -9,7 +9,7 @@
 
 #pragma once
 
-#include <algorithm> // find, find_if, max
+#include <algorithm> // find, find_if, max, min
 #include <array> // array
 #include <cstddef> // size_t, ptrdiff_t
 #include <cstdint> // int64_t, uint8_t, uint16_t, uint32_t, uint64_t
@@ -202,8 +202,18 @@ class builder
         const std::uint64_t done = static_cast<std::uint64_t>(at - b) + 1;
         const std::uint64_t guess = static_cast<std::uint64_t>(n) * static_cast<std::uint64_t>(e - b + 1) / done;
         const std::uint64_t grown = guess + (guess / 4) + 64; // a variable: GCC calls a cast of the sum useless where std::uint64_t is std::size_t
+        // (n is below 2^32: the input is smaller than 4 GiB; the sum cannot wrap)
+        const std::uint64_t wanted = (std::max)(grown, static_cast<std::uint64_t>(n) + (n / 2) + 64);
+        const std::uint64_t limit = document_data::max_nodes();
         doc.tape_size = n;
-        doc.reserve((std::max)(static_cast<std::size_t>(grown), n + (n / 2) + 64));
+        // LCOV_EXCL_START (a node array that fills the address space)
+        if (NLOHMANN_VIEW_UNLIKELY(n >= limit))
+        {
+            document_data::throw_bad_alloc(); // no room for another node
+        }
+        // LCOV_EXCL_STOP
+        // (a count beyond the limit is cut: the index does not grow beyond what can be addressed)
+        doc.reserve(static_cast<std::size_t>((std::min)(wanted, limit)));
         return doc.tape;
     }
 
@@ -816,7 +826,10 @@ indent_done:
             n->flags = flags;
             n->extra = extra;
             n->off = static_cast<std::uint32_t>(off);
-            set_integer_bits(*n, second);
+            // len is the low half of the second word, next the high half
+            // (not a native word over both, which swaps them on big-endian)
+            n->len = static_cast<std::uint32_t>(second);
+            n->next = static_cast<std::uint32_t>(second >> 32);
 #endif
             return n;
         }

include/nlohmann/detail/view/document_data.hpp

@@ -13,9 +13,10 @@
 #include <cstdint> // uint8_t, uint32_t
 #include <cstring> // memcpy
 #include <functional> // less
+#include <limits> // numeric_limits
 #include <map> // map
 #include <memory> // unique_ptr
-#include <new> // operator new, placement new
+#include <new> // bad_alloc, operator new, placement new
 #include <string> // string
 #include <vector> // vector
 
@@ -123,13 +124,30 @@ struct document_data
         tape_cap = inline_cap;
     }
 
-    /// make room for n nodes; keeps the first tape_size nodes
+    /// the largest node count whose size in bytes fits a std::size_t
+    static constexpr std::size_t max_nodes() noexcept
+    {
+        return (std::numeric_limits<std::size_t>::max)() / sizeof(node);
+    }
+
+    [[noreturn]] NLOHMANN_VIEW_NOINLINE static void throw_bad_alloc()
+    {
+        NLOHMANN_VIEW_THROW(std::bad_alloc());
+    }
+
+    /// make room for n nodes; keeps the first tape_size nodes (throws
+    /// std::bad_alloc for a count that does not fit the address space,
+    /// instead of wrapping around in n * sizeof(node))
     void reserve(std::size_t n)
     {
         if (n <= tape_cap)
         {
             return;
         }
+        if (NLOHMANN_VIEW_UNLIKELY(n > max_nodes()))
+        {
+            throw_bad_alloc();
+        }
         node* fresh = static_cast<node*>(::operator new (n * sizeof(node)));
         if (tape_size != 0)
         {

include/nlohmann/detail/view/edit.hpp

@@ -17,6 +17,7 @@
 #include <string> // string, to_string
 #include <type_traits> // decay, enable_if, integral_constant, is_arithmetic, is_convertible, is_floating_point, is_same, is_signed
 #include <utility> // forward
+#include <vector> // vector
 
 #include <nlohmann/json.hpp>
 #include <nlohmann/detail/view/document_data.hpp>
@@ -151,25 +152,23 @@ class editor
         {
             become_empty(o, value_t::object);
         }
-        // an existing member: assign it (and drop later duplicates, so that
-        // lookups, iteration, and materialize() agree)
+        // an existing member: assign the one that lookups find (the last
+        // one, should the key occur more than once), and drop the others, so
+        // that lookups, iteration, and materialize() agree. The key stays at
+        // the position of its first occurrence, as materialize() puts it.
         node* slot = nullptr;
-        bool duplicates = false;
+        std::size_t matches = 0;
         for (const node* k = nav::first(m_doc, o), *end = nav::end(m_doc, o); k != end; k = document_data::after(k + 1))
         {
             if (key_equals(*k, key))
             {
-                if (slot != nullptr)
-                {
-                    duplicates = true;
-                    break;
-                }
                 slot = const_cast<node*>(nav::value(k + 1)); // NOLINT(cppcoreguidelines-pro-type-const-cast): the nodes belong to this document
+                ++matches;
             }
         }
         if (slot != nullptr)
         {
-            if (duplicates)
+            if (matches > 1)
             {
                 erase_members(o, key, true);
             }
@@ -315,27 +314,38 @@ class editor
         return k.len == key.size() && (key.size() == 0 || std::memcmp(m_doc.str(k), key.data(), key.size()) == 0);
     }
 
-    /// remove the members with this key (all, or all but the first) from an object
-    std::size_t erase_members(node* o, string_view_t key, bool keep_first)
+    /// Remove the members with this key from an object: all of them, or all
+    /// but one. That one stays where the first occurrence is, but holds the
+    /// value of the last (the one that lookups find, which views may refer to).
+    std::size_t erase_members(node* o, string_view_t key, bool keep_one)
     {
         node* const h = block_of(m_doc, o, 0);
+        node last_value{}; // the entry of the value of the last member
+        node* const end = h + h->next;
+        if (keep_one)
+        {
+            for (node* r = h + 1; r != end; r += 2)
+            {
+                if (key_equals(*r, key))
+                {
+                    last_value = r[1];
+                }
+            }
+        }
         node* w = h + 1;
         std::size_t erased = 0;
         bool kept = false;
-        for (node* r = h + 1, *end = h + h->next; r != end; r += 2)
+        for (node* r = h + 1; r != end; r += 2)
         {
             const bool match = key_equals(*r, key);
-            if (match && (kept || !keep_first))
+            if (match && (kept || !keep_one))
             {
                 ++erased;
                 continue;
             }
+            w[0] = r[0];
+            w[1] = match ? last_value : r[1];
             kept = kept || match;
-            if (w != r)
-            {
-                w[0] = r[0];
-                w[1] = r[1];
-            }
             w += 2;
         }
         h->next = static_cast<std::uint32_t>(w - h);
@@ -347,9 +357,10 @@ class editor
     /// turn a null into an empty array/object in place
     static void become_empty(node* n, value_t k) noexcept
     {
+        const std::uint8_t linked = n->flags & node_flags::linked;
         *n = node{};
         n->kind = static_cast<std::uint8_t>(k);
-        n->flags = node_flags::is_new;
+        n->flags = static_cast<std::uint8_t>(node_flags::is_new | linked);
         n->next = 1;
     }
 
@@ -357,13 +368,17 @@ class editor
     /// include slot (if known).
     void assign(node* slot, const encoded& e, node* parent, bool parent_known)
     {
+        // an entry of a moved sequence links to the slot: it can take any extent
+        const std::uint8_t linked = slot->flags & node_flags::linked;
         if (e.region == nullptr)
         {
-            if (is_container(*slot) && slot->next > 1 && slot != m_doc.tape)
+            if (is_container(*slot) && slot->next > 1 && slot != m_doc.tape && linked == 0)
             {
                 // The slot spans its old elements in the enclosing sequence, but
                 // a scalar is one node: the enclosing container first switches to
-                // links (then the extent of the slot no longer matters).
+                // links (then the extent of the slot no longer matters). Looking
+                // for the container is linear in the size of the document, so
+                // links (which are marked in the slot) avoid it.
                 node* const p = parent_known ? parent : find_parent(m_doc, slot);
                 if (p != nullptr && ((p->flags & node_flags::moved) == 0 || moved_capacity(m_doc, p) == 0))
                 {
@@ -371,6 +386,7 @@ class editor
                 }
             }
             *slot = e.scalar;
+            slot->flags = static_cast<std::uint8_t>(slot->flags | linked);
             return;
         }
         // an array/object: the slot keeps its extent (so that the enclosing
@@ -379,11 +395,21 @@ class editor
         const node* const r = e.region;
         const std::uint32_t extent = is_container(*slot) ? slot->next : 1;
         const bool was_moved = (slot->flags & node_flags::moved) != 0;
+        // Everything that can throw happens before the slot changes: a slot
+        // that is a container without the moved flag would show its old
+        // elements. reserve_moved() makes the set_moved() below, which sets
+        // the flag, safe; the entry of `regions` exists already (encode()
+        // added it), so that the assignment at the end does not allocate.
+        if (!was_moved)
+        {
+            reserve_moved(m_doc);
+        }
         slot->kind = r->kind;
         slot->extra = 0;
         slot->len = r->len;
         slot->next = extent;
-        slot->flags = was_moved ? static_cast<std::uint8_t>(node_flags::moved | node_flags::is_new) : std::uint8_t{0};
+        // (set_moved() adds the moved flag to a slot that does not have it yet)
+        slot->flags = static_cast<std::uint8_t>((was_moved ? node_flags::moved | node_flags::is_new : 0) | linked);
         set_moved(m_doc, slot, e.region, 0);
         edit_state_of(m_doc).regions[e.region] = slot;
     }
@@ -600,6 +626,8 @@ class editor
         switch (static_cast<value_t>(n.kind))
         {
             case value_t::string:
+                // (an editable document only holds valid UTF-8, whatever the check of the other document was)
+                check_utf8(from.str(n), n.len);
                 return string_node(from.str(n), n.len);
             case value_t::number_integer:
             case value_t::number_unsigned:
@@ -663,100 +691,197 @@ class editor
         }
     }
 
+    // The subtrees are walked with an explicit stack (as materialize() does):
+    // the nesting depth is limited by memory only, not by the call stack.
+
     /// number of nodes of a subtree (containers, keys, scalars)
     template<bool E>
     static std::size_t count_nodes(const document_data& d, const node* n)
     {
-        if (!is_container(*n))
+        using walk = navigation<E>;
+        struct frame
         {
-            return 1;
-        }
-        const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
-        std::size_t r = 1;
-        for (const node* c = navigation<E>::first(d, n), *end = navigation<E>::end(d, n); c != end;)
+            const node* pos; ///< next element, or key of the next member
+            const node* end;
+            bool object;
+        };
+        std::vector<frame> open;
+        std::size_t r = 0;
+        for (;;)
         {
-            const node* const v = object ? c + 1 : c;
-            r += (object ? 1 : 0) + count_nodes<E>(d, navigation<E>::value(v));
-            c = document_data::after(v);
+            ++r;
+            if (is_container(*n))
+            {
+                open.push_back(frame{walk::first(d, n), walk::end(d, n), n->kind == static_cast<std::uint8_t>(value_t::object)});
+            }
+            // the next value: close finished containers, then step over the key
+            for (;;)
+            {
+                if (open.empty())
+                {
+                    return r;
+                }
+                frame& f = open.back();
+                if (f.pos == f.end)
+                {
+                    open.pop_back();
+                    continue;
+                }
+                const node* v = f.pos;
+                if (f.object)
+                {
+                    ++r; // the key
+                    ++v;
+                }
+                f.pos = document_data::after(v);
+                n = walk::value(v);
+                break;
+            }
         }
-        return r;
     }
 
-    /// copy a subtree (of any document) as a contiguous sequence; returns its end
+    /// copy a subtree (of any document) as a contiguous sequence of
+    /// count_nodes() nodes
     template<bool E>
-    node* fill_nodes(const document_data& d, const node* n, node* out)
+    void fill_nodes(const document_data& d, const node* n, node* out)
     {
-        if (!is_container(*n))
+        using walk = navigation<E>;
+        struct frame
         {
-            *out = copy_scalar(d, *n);
-            return out + 1;
-        }
-        node* const self = out++;
-        *self = plain_node(static_cast<value_t>(n->kind));
-        self->len = n->len;
-        const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
-        for (const node* c = navigation<E>::first(d, n), *end = navigation<E>::end(d, n); c != end;)
+            const node* pos; ///< next element, or key of the next member
+            const node* end;
+            bool object;
+            node* self;      ///< the container in the copy
+        };
+        std::vector<frame> open;
+        for (;;)
         {
-            if (object)
+            if (is_container(*n))
             {
-                *out++ = copy_scalar(d, *c);
-                ++c;
+                node* const self = out++;
+                *self = plain_node(static_cast<value_t>(n->kind));
+                self->len = n->len;
+                open.push_back(frame{walk::first(d, n), walk::end(d, n), n->kind == static_cast<std::uint8_t>(value_t::object), self});
+            }
+            else
+            {
+                *out++ = copy_scalar(d, *n);
+            }
+            // the next value: close finished containers, then copy the key
+            for (;;)
+            {
+                if (open.empty())
+                {
+                    return;
+                }
+                frame& f = open.back();
+                if (f.pos == f.end)
+                {
+                    f.self->next = static_cast<std::uint32_t>(out - f.self);
+                    open.pop_back();
+                    continue;
+                }
+                const node* v = f.pos;
+                if (f.object)
+                {
+                    *out++ = copy_scalar(d, *v);
+                    ++v;
+                }
+                f.pos = document_data::after(v);
+                n = walk::value(v);
+                break;
             }
-            out = fill_nodes<E>(d, navigation<E>::value(c), out);
-            c = document_data::after(c);
         }
-        self->next = static_cast<std::uint32_t>(out - self);
-        return out;
     }
 
     static std::size_t count_nodes(const BasicJsonType& j)
     {
-        std::size_t r = 1;
-        if (j.is_object())
+        using iterator = typename BasicJsonType::const_iterator;
+        struct frame
         {
-            for (const auto& member : j.items())
+            iterator pos;
+            iterator end;
+            bool object;
+        };
+        std::vector<frame> open;
+        const BasicJsonType* n = &j;
+        std::size_t r = 0;
+        for (;;)
+        {
+            ++r;
+            if (n->is_structured())
             {
-                r += 1 + count_nodes(member.value());
+                open.push_back(frame{n->cbegin(), n->cend(), n->is_object()});
+            }
+            for (;;)
+            {
+                if (open.empty())
+                {
+                    return r;
+                }
+                frame& f = open.back();
+                if (f.pos == f.end)
+                {
+                    open.pop_back();
+                    continue;
+                }
+                r += f.object ? 1 : 0; // the key
+                n = &*f.pos;
+                ++f.pos;
+                break;
             }
         }
-        else if (j.is_array())
-        {
-            for (const auto& e : j)
-            {
-                r += count_nodes(e);
-            }
-        }
-        return r;
     }
 
-    node* fill_nodes(const BasicJsonType& j, node* out)
+    void fill_nodes(const BasicJsonType& j, node* out)
     {
-        if (!j.is_structured())
+        using iterator = typename BasicJsonType::const_iterator;
+        struct frame
         {
-            *out = json_scalar(j);
-            return out + 1;
-        }
-        node* const self = out++;
-        *self = plain_node(j.type());
-        self->len = static_cast<std::uint32_t>(j.size());
-        if (j.is_object())
+            iterator pos;
+            iterator end;
+            bool object;
+            node* self; ///< the container in the copy
+        };
+        std::vector<frame> open;
+        const BasicJsonType* n = &j;
+        for (;;)
         {
-            for (const auto& member : j.items())
+            if (n->is_structured())
             {
-                check_utf8(member.key().data(), member.key().size());
-                *out++ = string_node(member.key().data(), member.key().size());
-                out = fill_nodes(member.value(), out);
+                node* const self = out++;
+                *self = plain_node(n->type());
+                self->len = static_cast<std::uint32_t>(n->size());
+                open.push_back(frame{n->cbegin(), n->cend(), n->is_object(), self});
+            }
+            else
+            {
+                *out++ = json_scalar(*n);
+            }
+            for (;;)
+            {
+                if (open.empty())
+                {
+                    return;
+                }
+                frame& f = open.back();
+                if (f.pos == f.end)
+                {
+                    f.self->next = static_cast<std::uint32_t>(out - f.self);
+                    open.pop_back();
+                    continue;
+                }
+                if (f.object)
+                {
+                    const auto& key = f.pos.key();
+                    check_utf8(key.data(), key.size());
+                    *out++ = string_node(key.data(), key.size());
+                }
+                n = &*f.pos;
+                ++f.pos;
+                break;
             }
         }
-        else
-        {
-            for (const auto& e : j)
-            {
-                out = fill_nodes(e, out);
-            }
-        }
-        self->next = static_cast<std::uint32_t>(out - self);
-        return out;
     }
 
     document_data& m_doc;

include/nlohmann/detail/view/edit_storage.hpp

@@ -63,6 +63,23 @@ inline node* alloc_nodes(document_data& d, std::size_t k)
     return r;
 }
 
+/// The capacity of the edit arena after it grows by n bytes (`used` of `cap`
+/// are taken): doubled, or what is needed plus some room, but never more than
+/// the 4 GiB - 1 bytes that the 32-bit offsets of nodes can address. An error
+/// if n more bytes do not fit even then.
+inline std::size_t text_capacity(std::size_t cap, std::size_t used, std::size_t n)
+{
+    constexpr std::size_t limit = 0xFFFFFFFFu;
+    if (NLOHMANN_VIEW_UNLIKELY(used > limit || n > limit - used))
+    {
+        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});
+    const std::size_t doubled = cap > limit / 2 ? limit : cap * 2;
+    return (std::max)(doubled, wanted);
+}
+
 /// copy n bytes into the edit arena and return their offset; a new buffer
 /// leaves the old one alive, so that string views into it remain valid
 inline std::uint32_t append_text(document_data& d, const char* s, std::size_t n)
@@ -70,11 +87,7 @@ inline std::uint32_t append_text(document_data& d, const char* s, std::size_t n)
     document_data::edit_state& e = edit_state_of(d);
     if (NLOHMANN_VIEW_UNLIKELY(e.text_cap - e.text_used < n))
     {
-        const std::size_t cap = (std::max)(e.text_cap * 2, e.text_used + n + 256);
-        if (cap > 0xFFFFFFFFu)
-        {
-            throw_out_of_range(416, "edits of 4 GiB or more are not supported by json_document"); // LCOV_EXCL_LINE (4 GiB)
-        }
+        const std::size_t cap = text_capacity(e.text_cap, e.text_used, n);
         std::unique_ptr<char[]> fresh(new char[cap]); // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
         if (e.text_used != 0)
         {
@@ -101,16 +114,12 @@ inline std::size_t moved_capacity(const document_data& d, const node* n) noexcep
     return d.edits->moved_cap[n->off];
 }
 
-/// let container n take its elements from `seq` (header node first)
-inline void set_moved(document_data& d, node* n, node* seq, std::size_t cap)
+/// Make room for one more moved container. This is the part of set_moved()
+/// that can throw: a caller that changes a node before it calls set_moved()
+/// calls this first, so that a failure leaves the node as it was.
+inline void reserve_moved(document_data& d)
 {
     document_data::edit_state& e = edit_state_of(d);
-    if ((n->flags & node_flags::moved) != 0)
-    {
-        e.moved[n->off] = seq;
-        e.moved_cap[n->off] = cap;
-        return;
-    }
     if (e.moved.size() >= 0xFFFFFFFFu)
     {
         throw_out_of_range(416, "more than 4294967295 edited arrays and objects are not supported by json_document"); // LCOV_EXCL_LINE
@@ -121,6 +130,20 @@ inline void set_moved(document_data& d, node* n, node* seq, std::size_t cap)
         e.moved.reserve((2 * e.moved.size()) + 16);
         e.moved_cap.reserve((2 * e.moved.size()) + 16);
     }
+}
+
+/// let container n take its elements from `seq` (header node first); cannot
+/// throw if n is moved already or reserve_moved() was called
+inline void set_moved(document_data& d, node* n, node* seq, std::size_t cap)
+{
+    document_data::edit_state& e = edit_state_of(d);
+    if ((n->flags & node_flags::moved) != 0)
+    {
+        e.moved[n->off] = seq;
+        e.moved_cap[n->off] = cap;
+        return;
+    }
+    reserve_moved(d);
     e.moved.push_back(seq);
     e.moved_cap.push_back(cap);
     n->off = static_cast<std::uint32_t>(e.moved.size() - 1);
@@ -146,6 +169,7 @@ inline node* block_of(document_data& d, node* n, std::size_t extra)
         set_moved(d, n, nh, cap);
         return nh;
     }
+    reserve_moved(d); // (so that set_moved() below cannot throw: the links are marked before)
     const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
     const std::size_t used = 1 + (static_cast<std::size_t>(n->len) * (object ? 2 : 1));
     const std::size_t cap = used + extra;
@@ -161,7 +185,7 @@ inline node* block_of(document_data& d, node* n, std::size_t extra)
         {
             *o++ = *c++; // the key
         }
-        make_link(*o, document_data::deref(c));
+        make_link(*o, const_cast<node*>(document_data::deref(c))); // NOLINT(cppcoreguidelines-pro-type-const-cast): the nodes belong to the document
         ++o;
         c = document_data::after(c);
     }

include/nlohmann/detail/view/errors.hpp

@@ -66,9 +66,8 @@ template<typename BasicJsonType>
 {
     if (f.code == error_code::input_too_large)
     {
-        // LCOV_EXCL_START (4 GiB)
-        NLOHMANN_VIEW_THROW(out_of_range::create(416, "input of 4 GiB or more is not supported by json_document", nullptr));
-        // LCOV_EXCL_STOP
+        // (the limit is detail::view::max_input_size: 4 GiB minus 16 bytes)
+        NLOHMANN_VIEW_THROW(out_of_range::create(416, "input of 4294967280 bytes or more is not supported by json_document", nullptr));
     }
     const BasicJsonType accepted = BasicJsonType::parse(src, src + size, nullptr, true, ignore_comments, ignore_trailing_commas);
     // LCOV_EXCL_START (only if parse() accepts what the view rejects: a bug)

include/nlohmann/detail/view/image.hpp

@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <algorithm> // sort
 #include <array> // array
 #include <cstddef> // size_t
 #include <cstdint> // int64_t, uint8_t, uint16_t, uint32_t, uint64_t
@@ -252,17 +253,25 @@ inline std::vector<std::uint8_t> save_image(const document_data& d)
     return image;
 }
 
-/// whether a number node matches its token the way the parser records it
-/// (after the bounds check)
-inline bool check_number(const node& n, const unsigned char* text)
+/// the parts of a number token that the checks need
+struct number_token
+{
+    const unsigned char* int_start;
+    std::size_t int_digits;
+    std::size_t frac_digits;
+    std::int64_t exponent;
+    bool negative;
+    bool is_float; ///< a fraction or an exponent
+};
+
+/// whether [s, s + len) is a JSON number (the grammar the parser accepts)
+inline bool scan_number_token(const unsigned char* s, std::size_t len, number_token& t)
 {
-    const std::size_t len = number_length(n);
-    const unsigned char* const s = text + n.off;
     const unsigned char* const e = s + len;
     const unsigned char* p = s;
-    const bool negative = *p == '-';
-    p += negative ? 1 : 0;
-    const unsigned char* const int_start = p;
+    t.negative = p != e && *p == '-';
+    p += t.negative ? 1 : 0;
+    t.int_start = p;
     if (p == e)
     {
         return false;
@@ -282,9 +291,9 @@ inline bool check_number(const node& n, const unsigned char* text)
     {
         return false;
     }
-    const auto int_digits = static_cast<std::size_t>(p - int_start);
-    std::size_t frac_digits = 0;
-    bool is_float = false;
+    t.int_digits = static_cast<std::size_t>(p - t.int_start);
+    t.frac_digits = 0;
+    t.is_float = false;
     if (p != e && *p == '.')
     {
         const unsigned char* const f0 = ++p;
@@ -296,10 +305,10 @@ inline bool check_number(const node& n, const unsigned char* text)
         {
             return false;
         }
-        frac_digits = static_cast<std::size_t>(p - f0);
-        is_float = true;
+        t.frac_digits = static_cast<std::size_t>(p - f0);
+        t.is_float = true;
     }
-    std::int64_t exponent = 0;
+    t.exponent = 0;
     if (p != e && (*p | 0x20u) == 'e')
     {
         ++p;
@@ -311,56 +320,171 @@ inline bool check_number(const node& n, const unsigned char* text)
         }
         while (p != e && is_digit(*p))
         {
-            exponent = exponent < 100000 ? (exponent * 10) + (*p - '0') : exponent;
+            t.exponent = t.exponent < 100000 ? (t.exponent * 10) + (*p - '0') : t.exponent;
             ++p;
         }
-        exponent = exp_negative ? -exponent : exponent;
-        is_float = true;
+        t.exponent = exp_negative ? -t.exponent : t.exponent;
+        t.is_float = true;
     }
-    if (p != e)
+    return p == e;
+}
+
+/// the digit layout the parser records for a float token (compaction
+/// writes "many" instead; the caller accepts both)
+inline std::uint16_t float_layout(const number_token& t)
+{
+    return static_cast<std::uint16_t>((t.int_digits < 255 ? t.int_digits : 255) | ((t.frac_digits < 255 ? t.frac_digits : 255) << 8u));
+}
+
+/// whether a float token (well-formed, per scan_number_token) is finite as
+/// double; parse() rejects floats that overflow, and as there, only a number
+/// whose magnitude could reach 1e308 needs the conversion
+inline bool float_token_finite(const unsigned char* s, std::size_t len, const number_token& t)
+{
+    if (static_cast<std::int64_t>(t.int_digits) + t.exponent > 300)
+    {
+        node n{};
+        n.kind = static_cast<std::uint8_t>(value_t::number_float);
+        n.len = static_cast<std::uint32_t>(len);
+        const auto v = float_value<double>(reinterpret_cast<const char*>(s), n); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+        return v <= (std::numeric_limits<double>::max)() && v >= -(std::numeric_limits<double>::max)();
+    }
+    return true;
+}
+
+/// whether an integer node matches its token the way the parser records it
+/// (after the bounds check; the token has at most 256 characters)
+inline bool check_integer(const node& n, const unsigned char* text)
+{
+    const std::size_t len = number_length(n);
+    const unsigned char* const s = text + n.off;
+    number_token t{};
+    if (!scan_number_token(s, len, t))
     {
         return false;
     }
-    if (n.kind == static_cast<std::uint8_t>(value_t::number_float))
-    {
-        // the digit layout the parser records (or "many", as compaction
-        // writes it), and a finite value
-        const auto layout = static_cast<std::uint16_t>((int_digits < 255 ? int_digits : 255) | ((frac_digits < 255 ? frac_digits : 255) << 8u));
-        if (n.extra != layout && n.extra != 0xFFFFu)
-        {
-            return false;
-        }
-        // parse() rejects floats that overflow; as there, only a number whose
-        // magnitude could reach 1e308 needs the conversion
-        if (static_cast<std::int64_t>(int_digits) + exponent > 300)
-        {
-            const auto v = float_value<double>(reinterpret_cast<const char*>(s), n); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
-            return v <= (std::numeric_limits<double>::max)() && v >= -(std::numeric_limits<double>::max)();
-        }
-        return true;
-    }
-    // integers: the token's value is the stored one; number_integer nodes of
-    // edits can be non-negative (as basic_json keeps the type of a value)
+    // the token's value is the stored one; number_integer nodes of edits can
+    // be non-negative (as basic_json keeps the type of a value)
     const bool integer = n.kind == static_cast<std::uint8_t>(value_t::number_integer);
-    if (is_float || int_digits > 20 || (negative && !integer))
+    if (t.is_float || t.int_digits > 20 || (t.negative && !integer))
     {
         return false;
     }
     // (at most 19 digits cannot overflow; 20 digits are compared with 2^64 - 1)
-    if (int_digits == 20 && std::memcmp(int_start, "18446744073709551615", 20) > 0)
+    if (t.int_digits == 20 && std::memcmp(t.int_start, "18446744073709551615", 20) > 0)
     {
         return false;
     }
     std::uint64_t m = 0;
-    for (const unsigned char* d = int_start; d != int_start + int_digits; ++d)
+    for (const unsigned char* d = t.int_start; d != t.int_start + t.int_digits; ++d)
     {
         m = (m * 10) + static_cast<std::uint64_t>(*d - '0');
     }
-    if (integer && m > (negative ? std::uint64_t{1} << 63u : (std::uint64_t{1} << 63u) - 1))
+    if (integer && m > (t.negative ? std::uint64_t{1} << 63u : (std::uint64_t{1} << 63u) - 1))
     {
         return false;
     }
-    return integer_bits(n) == (negative ? 0 - m : m);
+    return integer_bits(n) == (t.negative ? 0 - m : m);
+}
+
+/// a byte range of the text or of the decoded strings
+struct byte_range
+{
+    std::uint32_t off;
+    std::uint32_t len;
+};
+
+/// a float token and the digit layout its node records
+struct float_range
+{
+    std::uint32_t off;
+    std::uint32_t len;
+    std::uint16_t extra;
+};
+
+/// Run check once for each distinct range of ranges (which are within bounds
+/// and not empty). Ranges that are not identical must not overlap: save()
+/// writes every string and token to a place of its own, and nodes that share
+/// a value (copies within a document) share the whole range. This bounds the
+/// work by the size of the text, however many nodes point to the same bytes.
+template<typename Check>
+bool check_distinct_ranges(std::vector<byte_range>& ranges, Check check)
+{
+    std::sort(ranges.begin(), ranges.end(), [](const byte_range & a, const byte_range & b)
+    {
+        return a.off != b.off ? a.off < b.off : a.len < b.len;
+    });
+    std::size_t end = 0;
+    for (std::size_t i = 0; i < ranges.size(); ++i)
+    {
+        const byte_range r = ranges[i];
+        if (i != 0 && r.off == ranges[i - 1].off && r.len == ranges[i - 1].len)
+        {
+            continue;
+        }
+        if (r.off < end || !check(r))
+        {
+            return false;
+        }
+        end = static_cast<std::size_t>(r.off) + r.len;
+    }
+    return true;
+}
+
+/// Check the float nodes: each token once (nodes of the same token must
+/// record layouts that match it), tokens must not overlap.
+inline bool check_float_ranges(std::vector<float_range>& ranges, const unsigned char* text)
+{
+    std::sort(ranges.begin(), ranges.end(), [](const float_range & a, const float_range & b)
+    {
+        return a.off != b.off ? a.off < b.off : (a.len != b.len ? a.len < b.len : a.extra < b.extra);
+    });
+    std::size_t end = 0;
+    std::size_t i = 0;
+    while (i < ranges.size())
+    {
+        const float_range r = ranges[i];
+        if (r.off < end)
+        {
+            return false;
+        }
+        number_token t{};
+        const unsigned char* const s = text + r.off;
+        if (!scan_number_token(s, r.len, t) || !float_token_finite(s, r.len, t))
+        {
+            return false;
+        }
+        // the digit layout the parser records (or "many", as compaction writes it)
+        const std::uint16_t layout = float_layout(t);
+        for (; i < ranges.size() && ranges[i].off == r.off && ranges[i].len == r.len; ++i)
+        {
+            if (ranges[i].extra != layout && ranges[i].extra != 0xFFFFu)
+            {
+                return false;
+            }
+        }
+        end = static_cast<std::size_t>(r.off) + r.len;
+    }
+    return true;
+}
+
+/// the content checks of check_image: source strings as the parser leaves
+/// them (no quotes, backslashes, or control characters), decoded strings
+/// (valid UTF-8), and float tokens
+inline bool check_contents(const unsigned char* text, const unsigned char* arena,
+                           std::vector<byte_range>& source_strings, std::vector<byte_range>& decoded_strings,
+                           std::vector<float_range>& floats)
+{
+    return check_distinct_ranges(source_strings, [text](const byte_range & r)
+    {
+        const unsigned char* const b = text + r.off;
+        return scan_string_run(b, b + r.len) == b + r.len;
+    })
+    && check_distinct_ranges(decoded_strings, [arena](const byte_range & r)
+    {
+        return valid_utf8_prefix(arena + r.off, r.len) == r.len;
+    })
+    && check_float_ranges(floats, text);
 }
 
 /// Check the nodes of a loaded image against its text and decoded strings:
@@ -368,6 +492,12 @@ inline bool check_number(const node& n, const unsigned char* text)
 /// objects; keys; bounds; string contents (source strings as the parser
 /// leaves them: no quotes, backslashes, or control characters; all strings
 /// valid UTF-8); and number tokens.
+///
+/// The structure and the bounds are checked node by node. The contents of
+/// strings and of float tokens are checked afterwards, once for each distinct
+/// range (see check_distinct_ranges), so that the full check is linear in the
+/// size of the image plus the sorting of the ranges, and not in the number of
+/// nodes times the size of the text.
 inline bool check_image(const node* nodes, std::size_t count, const unsigned char* text, std::size_t text_size,
                         const unsigned char* arena, std::size_t arena_size, bool full)
 {
@@ -380,6 +510,9 @@ inline bool check_image(const node* nodes, std::size_t count, const unsigned cha
         bool expect_key;
     };
     std::vector<frame> stack;
+    std::vector<byte_range> source_strings;
+    std::vector<byte_range> decoded_strings;
+    std::vector<float_range> floats;
     const auto check_string = [&](const node & n) -> bool
     {
         if ((n.flags & ~node_flags::escaped) != 0 || n.extra != 0)
@@ -387,18 +520,16 @@ inline bool check_image(const node* nodes, std::size_t count, const unsigned cha
             return false;
         }
         const bool decoded = (n.flags & node_flags::escaped) != 0;
-        const unsigned char* const base = decoded ? arena : text;
         const std::size_t limit = decoded ? arena_size : text_size;
         if (n.off > limit || n.len > limit - n.off)
         {
             return false;
         }
-        if (!full)
+        if (full && n.len != 0)
         {
-            return true;
+            (decoded ? decoded_strings : source_strings).push_back(byte_range{n.off, n.len});
         }
-        const unsigned char* const b = base + n.off;
-        return decoded ? valid_utf8_prefix(b, n.len) == n.len : scan_string_run(b, b + n.len) == b + n.len;
+        return true;
     };
     // bounds of a number token; the recorded digit layout must lie within it
     const auto number_in_bounds = [&](const node & n) -> bool
@@ -440,7 +571,7 @@ inline bool check_image(const node* nodes, std::size_t count, const unsigned cha
         }
         if (i == count)
         {
-            return stack.empty();
+            return stack.empty() && (!full || check_contents(text, arena, source_strings, decoded_strings, floats));
         }
         if (i != 0 && stack.empty())
         {
@@ -482,10 +613,23 @@ inline bool check_image(const node* nodes, std::size_t count, const unsigned cha
             case value_t::number_integer:
             case value_t::number_unsigned:
             case value_t::number_float:
-                if (n.flags != 0 || !number_in_bounds(n) || (full && !check_number(n, text)))
+                if (n.flags != 0 || !number_in_bounds(n))
                 {
                     return false;
                 }
+                if (full)
+                {
+                    // (the contents of float tokens are checked later; the token of an
+                    // integer has at most 256 characters)
+                    if (n.kind == static_cast<std::uint8_t>(value_t::number_float))
+                    {
+                        floats.push_back(float_range{n.off, n.len, n.extra});
+                    }
+                    else if (!check_integer(n, text))
+                    {
+                        return false;
+                    }
+                }
                 break;
             case value_t::array:
             case value_t::object:
@@ -594,6 +738,7 @@ inline void load_image(document_data& d, const std::uint8_t* image, std::size_t
         }
     }
     build_object_indexes(d);
+    std::vector<std::uint32_t>().swap(d.large_objects); // (only needed while building)
     d.discarded = false;
 }
 

include/nlohmann/detail/view/input.hpp

@@ -9,7 +9,7 @@
 #pragma once
 
 #include <string> // basic_string, char_traits, string
-#include <type_traits> // decay, integral_constant, is_array, is_lvalue_reference, is_pointer, is_same, remove_reference
+#include <type_traits> // decay, integral_constant, is_array, is_const, is_integral, is_lvalue_reference, is_pointer, is_same, remove_reference
 #include <utility> // forward
 
 #include <nlohmann/json.hpp>
@@ -28,12 +28,12 @@ namespace view
 /// how a document takes its input
 enum class input_kind
 {
-    move_string,  ///< rvalue std::string: owned without a copy
+    move_string,  ///< non-const rvalue std::string: owned without a copy
     c_string,     ///< const char* (NUL-terminated): borrowed
     char_array,   ///< char array (e.g. a string literal): borrowed
     borrow_range, ///< lvalue contiguous byte container, or std::string_view: borrowed
-    copy_range,   ///< rvalue contiguous byte container: copied
-    adapter,      ///< anything else parse() accepts (streams, wide strings, ...): read into a buffer
+    copy_range,   ///< rvalue contiguous byte container (a const rvalue std::string too): copied
+    adapter,      ///< streams, wide strings, and the rest of what the library's input adapter reads: read into a buffer
 };
 
 template<typename InputType>
@@ -52,13 +52,20 @@ struct classify_input
     static constexpr input_kind value =
         std::is_array<R>::value ? input_kind::char_array
         : std::is_pointer<D>::value ? input_kind::c_string
-        : (is_rvalue && std::is_same<D, std::string>::value) ? input_kind::move_string
+        : (is_rvalue && !std::is_const<R>::value && std::is_same<D, std::string>::value) ? input_kind::move_string
         : (is_bytes && (!is_rvalue || is_string_view)) ? input_kind::borrow_range
         : is_bytes ? input_kind::copy_range
         : input_kind::adapter;
     // NOLINTEND(readability-avoid-nested-conditional-operator)
 };
 
+/// an integer type other than bool: a length passed where a flag is expected
+template<typename T>
+struct is_integer_not_bool : std::is_integral<T> {};
+
+template<>
+struct is_integer_not_bool<bool> : std::false_type {};
+
 /// std::basic_string guarantees a NUL at data()[size()] (the parser's sentinel)
 template<typename T>
 struct is_std_string : std::false_type {};

include/nlohmann/detail/view/lookup.hpp

@@ -11,6 +11,8 @@
 #include <cstddef> // size_t
 #include <cstdint> // uint16_t, uint32_t, uint64_t
 #include <cstring> // memcmp, memcpy
+#include <limits> // numeric_limits
+#include <type_traits> // integral_constant, is_integral, is_same
 
 #include <nlohmann/json.hpp>
 #include <nlohmann/detail/view/document_data.hpp>
@@ -82,8 +84,9 @@ class short_key
     std::uint64_t m_b = 0;
 };
 
-/// the key node of the first member of an object with the given key, or
-/// nullptr; most keys are rejected by their length, from the index alone
+/// the key node of the last member of an object with the given key, or
+/// nullptr (the last one, as materialize() and parse() keep it); most keys are
+/// rejected by their length, from the index alone
 template<bool Editable>
 const node* find_member(const document_data& d, const node* object, const char* key, std::size_t n) noexcept
 {
@@ -94,6 +97,7 @@ const node* find_member(const document_data& d, const node* object, const char*
     }
     const node* const end = nav::end(d, object);
     const auto* const k = reinterpret_cast<const unsigned char*>(key); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    const node* last = nullptr;
     if (NLOHMANN_VIEW_LIKELY(n <= 16))
     {
         const short_key probe(k, n);
@@ -101,19 +105,37 @@ const node* find_member(const document_data& d, const node* object, const char*
         {
             if (m->len == n && probe.matches(reinterpret_cast<const unsigned char*>(d.str(*m)))) // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
             {
-                return m;
+                last = m;
             }
         }
-        return nullptr;
+        return last;
     }
     for (const node* m = nav::first(d, object); m != end; m = document_data::after(m + 1))
     {
         if (m->len == n && std::memcmp(d.str(*m), key, n) == 0)
         {
-            return m;
+            last = m;
         }
     }
-    return nullptr;
+    return last;
+}
+
+/// whether an integer type is accepted as an array index by the view's
+/// operator[] and at(): every integer type but bool and size_t, which has its
+/// own overload
+template<typename T>
+struct is_index_type : std::integral_constant < bool,
+    std::is_integral<T>::value && !std::is_same<T, bool>::value && !std::is_same<T, std::size_t>::value >
+{};
+
+/// an integer as an index: negative values, and values that do not fit a
+/// size_t, map to the largest size_t (out of range for every array)
+template<typename SizeType, typename IntegerType>
+SizeType to_index(IntegerType idx) noexcept
+{
+    const IntegerType zero = 0;
+    const auto result = static_cast<SizeType>(idx);
+    return (idx < zero || static_cast<IntegerType>(result) != idx) ? (std::numeric_limits<SizeType>::max)() : result;
 }
 
 /// the entry of the element of an array at an index below its size (a link

include/nlohmann/detail/view/node.hpp

@@ -29,6 +29,11 @@ static_assert(static_cast<std::uint8_t>(value_t::null) == 0 && static_cast<std::
               && static_cast<std::uint8_t>(value_t::number_unsigned) == 6 && static_cast<std::uint8_t>(value_t::number_float) == 7,
               "the node format depends on the numbering of value_t");
 
+/// The largest input a document accepts, in bytes. Offsets and node counts are
+/// 32 bits wide; the limit keeps 16 bytes (the width of the scanner's steps)
+/// below 2^32, so that a position one step past the end of the text fits.
+static constexpr std::size_t max_input_size = 0xFFFFFFEFu;
+
 /// node flags
 struct node_flags
 {
@@ -38,6 +43,7 @@ struct node_flags
     static constexpr std::uint8_t is_true = 4; ///< boolean value
     static constexpr std::uint8_t moved = 8;   ///< array/object: the elements live in a separate sequence (editable documents)
     static constexpr std::uint8_t is_new = 16; ///< written by an edit: no source position
+    static constexpr std::uint8_t linked = 32; ///< an entry of a moved sequence links to this value (editable documents): its extent in the parsed layout no longer matters
 };
 
 /// kind of an entry of an edited sequence that stands for a value stored
@@ -52,7 +58,7 @@ struct node
 {
     std::uint8_t kind;   ///< value_t, or kind_link
     std::uint8_t flags;  ///< node_flags
-    std::uint16_t extra; ///< numbers: integer digits (low byte) and fraction digits (high byte), 255 = "many"; objects: number of the hash index; otherwise 0
+    std::uint16_t extra; ///< numbers: integer digits (low byte) and fraction digits (high byte), 255 = "many"; objects: number of the hash index (1-based, 0 = none); otherwise 0
     std::uint32_t off;   ///< source offset (string content, number token, literal, bracket); arena offset if escaped/edited; number of the element sequence if moved
     std::uint32_t len;   ///< string: decoded bytes; float: token bytes; array/object: element count
     std::uint32_t next;  ///< array/object: number of nodes of the subtree (its extent in the enclosing sequence)
@@ -72,24 +78,36 @@ NLOHMANN_VIEW_ALWAYS_INLINE const node* link_target(const node& n) noexcept
     return t;
 }
 
-inline void make_link(node& n, const node* target) noexcept
+/// let the entry n stand for the value at target (and mark the value)
+inline void make_link(node& n, node* target) noexcept
 {
+    target->flags = static_cast<std::uint8_t>(target->flags | node_flags::linked);
     n = node{};
     n.kind = kind_link;
     std::memcpy(reinterpret_cast<unsigned char*>(&n) + 8, static_cast<const void*>(&target), sizeof(const node*)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
 }
 
-/// the converted value of an integer node (stored in len/next)
+/// the converted value of an integer node: len is its low half, next its high
+/// half (on little-endian targets the two words are the value in memory)
 NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t integer_bits(const node& n) noexcept
 {
+#if NLOHMANN_VIEW_LITTLE_ENDIAN
     std::uint64_t v = 0;
     std::memcpy(&v, reinterpret_cast<const unsigned char*>(&n) + 8, 8); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
     return v;
+#else
+    return static_cast<std::uint64_t>(n.len) | (static_cast<std::uint64_t>(n.next) << 32);
+#endif
 }
 
 NLOHMANN_VIEW_ALWAYS_INLINE void set_integer_bits(node& n, std::uint64_t v) noexcept
 {
+#if NLOHMANN_VIEW_LITTLE_ENDIAN
     std::memcpy(reinterpret_cast<unsigned char*>(&n) + 8, &v, 8); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+#else
+    n.len = static_cast<std::uint32_t>(v);
+    n.next = static_cast<std::uint32_t>(v >> 32);
+#endif
 }
 
 /// token length of a number node

include/nlohmann/detail/view/object_index.hpp

@@ -22,8 +22,14 @@
 // large objects). An object with document_data::index_min_members members or
 // more gets an open-addressing table after parsing; its node stores the
 // number of the table (1-based) in `extra`. A slot holds the offset of a key
-// node from its object node (0: empty). Of duplicate keys, the first is kept,
-// as for the linear search.
+// node from its object node (0: empty). Of duplicate keys, the last is kept,
+// as for the linear search, and as basic_json::parse() does.
+//
+// The hash is not seeded, so keys chosen to collide could make the build
+// quadratic. A key therefore sits at most index_max_displacement slots away
+// from its home slot; if a key would sit further away, the table is dropped
+// and the object is searched linearly (like a small one). For the same
+// reason, a lookup visits at most index_max_displacement + 1 slots.
 
 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -31,6 +37,11 @@ namespace detail
 namespace view
 {
 
+/// the farthest a key may sit from its home slot (a table with at most half of
+/// its slots in use gives random keys a distance of about 50 for millions of
+/// members; and every member costs at most this many steps while building)
+constexpr std::size_t index_max_displacement = 64;
+
 /// hash of a key: its bytes, eight at a time, in a fixed byte order
 inline std::uint64_t key_hash(const char* s, std::size_t n) noexcept
 {
@@ -68,27 +79,44 @@ inline void build_object_index(document_data& d, node* obj)
     d.index_slots.resize(start + cap, 0);
     std::uint32_t* const slots = d.index_slots.data() + start;
     const std::size_t mask = cap - 1;
+    bool degenerate = false;
     for (const node* k = document_data::first_child(obj), *end = document_data::child_end(obj); k != end; k = document_data::after(k + 1))
     {
         const char* const key = d.str(*k);
         const std::uint64_t hash = key_hash(key, k->len); // (a cast of the call would be useless where std::uint64_t is std::size_t)
         std::size_t i = static_cast<std::size_t>(hash) & mask;
         bool duplicate = false;
+        std::size_t distance = 0;
         while (slots[i] != 0)
         {
             const node* const other = obj + slots[i];
             if (other->len == k->len && (k->len == 0 || std::memcmp(d.str(*other), key, k->len) == 0))
             {
-                duplicate = true; // keep the first
+                duplicate = true; // keep the last: the key's slot now leads to this member
+                slots[i] = static_cast<std::uint32_t>(k - obj);
+                break;
+            }
+            if (++distance > index_max_displacement)
+            {
+                degenerate = true; // too many keys share a home region
                 break;
             }
             i = (i + 1) & mask;
         }
+        if (degenerate)
+        {
+            break;
+        }
         if (!duplicate)
         {
             slots[i] = static_cast<std::uint32_t>(k - obj);
         }
     }
+    if (degenerate)
+    {
+        d.index_slots.resize(start); // no table: the object is searched linearly
+        return;
+    }
     d.indexes.push_back(document_data::object_index{start, static_cast<std::uint32_t>(mask)});
     obj->extra = static_cast<std::uint16_t>(d.indexes.size());
 }
@@ -102,7 +130,7 @@ inline void build_object_indexes(document_data& d)
     }
 }
 
-/// the key node of the first member with this key of an indexed object, or
+/// the key node of the last member with this key of an indexed object, or
 /// nullptr
 inline const node* find_indexed(const document_data& d, const node* obj, const char* key, std::size_t n) noexcept
 {
@@ -110,7 +138,7 @@ inline const node* find_indexed(const document_data& d, const node* obj, const c
     const std::uint32_t* const slots = d.index_slots.data() + ix.start;
     const std::uint64_t hash = key_hash(key, n); // (a cast of the call would be useless where std::uint64_t is std::size_t)
     std::size_t i = static_cast<std::size_t>(hash) & ix.mask;
-    for (;;)
+    for (std::size_t distance = 0; distance <= index_max_displacement; ++distance)
     {
         const std::uint32_t s = slots[i];
         if (s == 0)
@@ -124,6 +152,7 @@ inline const node* find_indexed(const document_data& d, const node* obj, const c
         }
         i = (i + 1) & ix.mask;
     }
+    return nullptr; // (no key sits further from its home slot)
 }
 
 }  // namespace view

include/nlohmann/detail/view/serializer.hpp

@@ -48,7 +48,13 @@ class output_buffer
 
     void finish()
     {
-        m_out.resize(static_cast<std::size_t>(m_pos - m_out.data()));
+        const auto size = static_cast<std::size_t>(m_pos - m_out.data());
+        m_out.resize(size);
+        // do not keep a buffer that was sized for a much larger output
+        if (m_out.capacity() > 1024 && m_out.capacity() / 2 > size)
+        {
+            m_out.shrink_to_fit();
+        }
     }
 
     NLOHMANN_VIEW_ALWAYS_INLINE void reserve(std::size_t n)
@@ -356,16 +362,6 @@ class view_serializer
     }
 
   private:
-    /*!
-    @brief the compact output without ensure_ascii (the default dump())
-
-    The same walk as dump(), with the write position in a local variable
-    (stores through char pointers would otherwise force a reload of the
-    buffer's members after each one), and with strings and number tokens of
-    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.
-    */
     /// 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
@@ -404,6 +400,16 @@ class view_serializer
         return option;
     }
 
+    /*!
+    @brief the compact output without ensure_ascii (the default dump())
+
+    The same walk as dump(), with the write position in a local variable
+    (stores through char pointers would otherwise force a reload of the
+    buffer's members after each one), and with strings and number tokens of
+    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.
+    */
     template<bool SourceNumbers>
     void dump_compact(const node* root)
     {
@@ -525,7 +531,7 @@ class view_serializer
                         room(n->len);
                         copy(src + n->off, n->len);
                     }
-                    else if (std::is_same<number_float_t, double>::value)
+                    else if (enabled(std::is_same<number_float_t, double>::value))
                     {
                         room(64);
                         w = write_double_at(w, *n);
@@ -752,9 +758,14 @@ class view_serializer
             {
                 *w = '-';
                 w += d.negative ? 1 : 0;
-                // (without leading zeros, all digits of the token count)
-                const unsigned char lead = first[d.negative ? 1 : 0];
-                return lead != '0' ? ::nlohmann::detail::dtoa_impl::write_short_decimal(w, d.w, static_cast<int>(int_digits + frac_digits), static_cast<int>(d.exponent))
+                // (without leading zeros, all digits of the token count; the
+                // check also keeps an image that was only checked for bounds,
+                // whose token may not be made of digits, from the counted
+                // overload)
+                const auto& powers = ::nlohmann::detail::dtoa_impl::powers_of_ten_16();
+                const unsigned count = int_digits + frac_digits;
+                return count - 1u < 15u && d.w >= powers[count - 1u] && d.w < powers[count]
+                       ? ::nlohmann::detail::dtoa_impl::write_short_decimal(w, d.w, static_cast<int>(count), static_cast<int>(d.exponent))
                        : ::nlohmann::detail::dtoa_impl::write_short_decimal(w, d.w, static_cast<int>(d.exponent));
             }
             return write_double_value_at(w, decimal_to_float<double>(d)); // (without reading the token again)

include/nlohmann/detail/view/simd.hpp

@@ -35,7 +35,8 @@
 #else
     #define NLOHMANN_VIEW_NEON 0
 #endif
-#if !defined(JSON_VIEW_NO_SIMD) && !NLOHMANN_VIEW_NEON && (defined(__SSE2__) || defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2))
+// (x86 only: other targets can define __SSE2__ as well, e.g., WebAssembly with -msse2, but have no <cpuid.h>)
+#if !defined(JSON_VIEW_NO_SIMD) && !NLOHMANN_VIEW_NEON && (defined(__x86_64__) || defined(__i386__) || defined(_M_X64) || defined(_M_IX86)) && (defined(__SSE2__) || defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2))
     #include <emmintrin.h>
     #define NLOHMANN_VIEW_SSE2 1
 #else

include/nlohmann/json_view.hpp

@@ -7,16 +7,18 @@
 // SPDX-License-Identifier: MIT
 
 /****************************************************************************\
- * Zero-copy, read-only view of a parsed JSON text.                          *
+ * Zero-copy view of a parsed JSON text.                                     *
  *                                                                           *
  * json_document::parse() builds a flat index of the values of a JSON text   *
  * (16 bytes per value) instead of a tree of basic_json values. Strings and  *
  * numbers stay in the source text; only strings with escapes are decoded,   *
  * into one buffer. json_view is a handle to one value of the document, with *
  * the read-only part of the basic_json interface; materialize() turns a     *
- * subtree into the basic_json value that parse() would produce.             *
+ * subtree into the basic_json value that parse() would produce. An editable *
+ * document (json_editable_document) also has set(), push_back(), insert(),  *
+ * and erase(): edits never write to the source text, and views stay valid.  *
  *                                                                           *
- * The source text must outlive a document that borrows it (lvalue byte     *
+ * The source text must outlive a document that borrows it (lvalue byte      *
  * containers, C strings); rvalue strings, streams, and other inputs are     *
  * owned by the document.                                                    *
 \****************************************************************************/
@@ -24,6 +26,7 @@
 #ifndef INCLUDE_NLOHMANN_JSON_VIEW_HPP_
 #define INCLUDE_NLOHMANN_JSON_VIEW_HPP_
 
+#include <algorithm> // all_of, min
 #include <cstddef> // size_t
 #include <cstdint> // uint8_t, uint32_t
 #include <cstring> // memcpy, strlen
@@ -181,12 +184,6 @@ class basic_json_view
         return type() == value_t::discarded;
     }
 
-    /// false for discarded views
-    explicit operator bool() const noexcept
-    {
-        return m_node != nullptr;
-    }
-
     /// the name of the type, as basic_json::type_name()
     const char* type_name() const noexcept
     {
@@ -246,13 +243,18 @@ class basic_json_view
     // element access //
     ////////////////////
 
-    /// the value of the member with this key (the first one, should the key
-    /// occur more than once); a discarded view if there is none. Throws
-    /// type_error.305 if this is not an object.
+    /// the value of the member with this key (the last one, should the key
+    /// occur more than once); a discarded view if there is none, or if this
+    /// is a discarded view (so that v["a"]["b"] is safe). Throws type_error.305
+    /// if this is any other value but an object.
     NLOHMANN_VIEW_ALWAYS_INLINE basic_json_view operator[](string_view_t key) const
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_object()))
         {
+            if (is_discarded())
+            {
+                return basic_json_view();
+            }
             detail::view::throw_type_error(305, "cannot use operator[] with a string argument with ", type_name());
         }
         return lookup(key);
@@ -269,31 +271,43 @@ class basic_json_view
     }
 
     /// the element at this index; a discarded view if the index is out of
-    /// range. Throws type_error.305 if this is not an array.
+    /// range, or if this is a discarded view. Throws type_error.305 if this is
+    /// any other value but an array.
     basic_json_view operator[](size_type idx) const
     {
         if (NLOHMANN_VIEW_UNLIKELY(!is_array()))
         {
+            if (is_discarded())
+            {
+                return basic_json_view();
+            }
             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();
     }
 
-    /// (an int argument would be ambiguous between size_type and const char*)
-    basic_json_view operator[](int idx) const
+    /// any other integer type (int, unsigned, long, std::int64_t, ...; a
+    /// single overload for size_type alone would be ambiguous for all of them
+    /// and for const char*); negative values are out of range
+    template < typename IntegerType, typename std::enable_if < detail::view::is_index_type<IntegerType>::value, int >::type = 0 >
+    basic_json_view operator[](IntegerType idx) const
     {
-        return operator[](static_cast<size_type>(idx));
+        return operator[](detail::view::to_index<size_type>(idx));
     }
 
     /// the value a JSON pointer refers to; a discarded view if a key is
-    /// missing or an index is out of range. Other errors throw what const
-    /// basic_json::operator[] throws.
+    /// missing or an index is out of range, or if this is a discarded view.
+    /// Other errors throw what const basic_json::operator[] throws.
     basic_json_view operator[](const json_pointer& ptr) const
     {
+        if (NLOHMANN_VIEW_UNLIKELY(is_discarded()))
+        {
+            return basic_json_view();
+        }
         return detail::view::resolve_pointer(*this, detail::json_pointer_access::reference_tokens(ptr), detail::view::pointer_mode::unchecked);
     }
 
-    /// the value of the member with this key (the first one, should the key
+    /// the value of the member with this key (the last one, should the key
     /// occur more than once). Throws type_error.304 if this is not an object,
     /// and out_of_range.403 if there is no such member.
     basic_json_view at(string_view_t key) const
@@ -303,7 +317,7 @@ class basic_json_view
             detail::view::throw_type_error(304, "cannot use at() with ", type_name());
         }
         const basic_json_view r = lookup(key);
-        if (NLOHMANN_VIEW_UNLIKELY(!r))
+        if (NLOHMANN_VIEW_UNLIKELY(r.is_discarded()))
         {
             detail::view::throw_out_of_range(403, detail::concat("key '", std::string(key.data(), key.size()), "' not found"));
         }
@@ -335,9 +349,12 @@ class basic_json_view
         return basic_json_view(m_doc, navigation::value(detail::view::element_at<Editable>(*m_doc, m_node, idx)));
     }
 
-    basic_json_view at(int idx) const
+    /// any other integer type, see operator[]; negative values are out of
+    /// range
+    template < typename IntegerType, typename std::enable_if < detail::view::is_index_type<IntegerType>::value, int >::type = 0 >
+    basic_json_view at(IntegerType idx) const
     {
-        return at(static_cast<size_type>(idx));
+        return at(detail::view::to_index<size_type>(idx));
     }
 
     /// the value a JSON pointer refers to; throws what basic_json::at()
@@ -348,7 +365,7 @@ class basic_json_view
     }
 
     /// the member with this key converted to T, or the default value if there
-    /// is no such member (the first one, should the key occur more than
+    /// is no such member (the last one, should the key occur more than
     /// once). Throws type_error.306 if this is not an object.
     template < typename T, typename std::enable_if < !std::is_same<typename std::decay<T>::type, const char*>::value, int >::type = 0 >
     T value(string_view_t key, const T& default_value) const
@@ -358,7 +375,7 @@ class basic_json_view
             detail::view::throw_type_error(306, "cannot use value() with ", type_name());
         }
         const basic_json_view r = lookup(key);
-        return r ? r.template get<T>() : default_value;
+        return r.is_discarded() ? default_value : r.template get<T>();
     }
 
     string_t value(string_view_t key, const char* default_value) const
@@ -377,7 +394,7 @@ class basic_json_view
             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 ? r.template get<T>() : default_value;
+        return r.is_discarded() ? default_value : r.template get<T>();
     }
 
     string_t value(const json_pointer& ptr, const char* default_value) const
@@ -413,7 +430,7 @@ class basic_json_view
     // lookup //
     ////////////
 
-    /// an iterator to the member with this key (the first one, should the
+    /// an iterator to the member with this key (the last one, should the
     /// key occur more than once), or end(); end() also for non-objects
     iterator find(string_view_t key) const
     {
@@ -455,7 +472,7 @@ class basic_json_view
     /// basic_json::contains())
     bool contains(const json_pointer& ptr) const
     {
-        return static_cast<bool>(detail::view::resolve_pointer(*this, detail::json_pointer_access::reference_tokens(ptr), detail::view::pointer_mode::contains));
+        return !detail::view::resolve_pointer(*this, detail::json_pointer_access::reference_tokens(ptr), detail::view::pointer_mode::contains).is_discarded();
     }
 
     /// 1 if this is an object with a member with this key, else 0 (duplicate
@@ -714,7 +731,7 @@ class basic_json_view
     }
 
     /// the number of source bytes of this value (estimated for values with
-    /// decoded strings)
+    /// decoded strings); the estimate sizes the output buffer of dump()
     std::size_t source_extent() const noexcept
     {
         if (editable() && m_doc->edits != nullptr)
@@ -722,20 +739,33 @@ class basic_json_view
             // positions of moved and new values are not source offsets
             return m_node == m_doc->tape ? m_doc->size + m_doc->edits->text_used : 64;
         }
-        const node* const next = document_data::after(m_node);
-        const bool in_source = (m_node->flags & detail::view::node_flags::storage) == 0;
-        if (!in_source)
+        const node* const end = m_doc->tape + m_doc->tape_size;
+        if ((m_node->flags & detail::view::node_flags::storage) != 0)
         {
             return m_node->len;
         }
-        if (next != m_doc->tape + m_doc->tape_size && (next->flags & detail::view::node_flags::storage) == 0 && next->off >= m_node->off)
+        // the value ends where the next node in the source begins; nodes
+        // with decoded strings (their offset is in the arena) are skipped,
+        // but only a few of them, to keep the walk short
+        const node* next = document_data::after(m_node);
+        for (int skipped = 0; next != end && skipped < 16; ++skipped, ++next)
         {
-            return next->off - m_node->off;
+            if ((next->flags & detail::view::node_flags::storage) == 0)
+            {
+                return next->off >= m_node->off ? next->off - m_node->off : 0;
+            }
         }
-        return m_doc->size - m_node->off;
+        if (next == end)
+        {
+            return m_doc->size - m_node->off;
+        }
+        // the end is unknown: assume a few bytes per node, the output buffer
+        // grows should the value be larger
+        const auto nodes = static_cast<std::size_t>(document_data::after(m_node) - m_node);
+        return (std::min)(m_doc->size - m_node->off, static_cast<std::size_t>(1024) + nodes * 16);
     }
 
-    /// the value of the first member with this key, or a discarded view
+    /// the value of the last member with this key, or a discarded view
     /// (object required)
     NLOHMANN_VIEW_ALWAYS_INLINE basic_json_view lookup(string_view_t key) const noexcept
     {
@@ -869,6 +899,13 @@ class basic_json_document
         return d;
     }
 
+    /// parse(ptr, len) does not compile: len would convert to allow_exceptions
+    /// and ptr be read as a C string (as for the overloads of parse_copy,
+    /// accept, and read below)
+    template<typename InputType, typename IntegerType, typename... Flags>
+    static typename std::enable_if<detail::view::is_integer_not_bool<IntegerType>::value, basic_json_document>::type
+    parse(InputType&& input, IntegerType value, Flags&&... flags) = delete;
+
     /// parse [first, last)
     template<typename IteratorType, typename std::enable_if<
                  std::is_base_of<std::input_iterator_tag, typename std::iterator_traits<IteratorType>::iterator_category>::value, int>::type = 0>
@@ -896,6 +933,10 @@ class basic_json_document
         return d;
     }
 
+    template<typename InputType, typename IntegerType, typename... Flags>
+    static typename std::enable_if<detail::view::is_integer_not_bool<IntegerType>::value, basic_json_document>::type
+    parse_copy(InputType&& input, IntegerType value, Flags&&... flags) = delete;
+
     /// check whether the input is valid JSON (the result of basic_json::accept)
     template<typename InputType>
     static bool accept(InputType&& input, const bool ignore_comments = false, const bool ignore_trailing_commas = false)
@@ -905,6 +946,10 @@ class basic_json_document
         return !d.is_discarded();
     }
 
+    template<typename InputType, typename IntegerType, typename... Flags>
+    static typename std::enable_if<detail::view::is_integer_not_bool<IntegerType>::value, bool>::type
+    accept(InputType&& input, IntegerType value, Flags&&... flags) = delete;
+
     /// parse into this document, reusing its memory
     template<typename InputType>
     // flawfinder: ignore (a member function, not POSIX read())
@@ -917,12 +962,17 @@ class basic_json_document
                   std::integral_constant<detail::view::input_kind, detail::view::classify_input<InputType>::value> {});
     }
 
+    template<typename InputType, typename IntegerType, typename... Flags>
+    // flawfinder: ignore (a member function, not POSIX read())
+    typename std::enable_if<detail::view::is_integer_not_bool<IntegerType>::value, void>::type
+    read(InputType&& input, IntegerType value, Flags&&... flags) = delete;
+
     ////////////
     // access //
     ////////////
 
     /// the root value (discarded if parsing failed without exceptions)
-    view_type root() const noexcept
+    view_type root() const& noexcept
     {
         if (!m_data || m_data->discarded)
         {
@@ -931,6 +981,9 @@ class basic_json_document
         return view_type(m_data.get(), m_data->tape);
     }
 
+    /// deleted: the view of a temporary document would dangle
+    view_type root() const&& = delete;
+
     bool is_discarded() const noexcept
     {
         return !m_data || m_data->discarded;
@@ -990,6 +1043,8 @@ class basic_json_document
         // (edits link to the nodes of the index, which then stays in place)
         const bool shrink_tape = d.tape != d.inline_tape && d.tape_size != d.tape_cap && d.edits == nullptr;
         const bool into_header = d.tape_size <= d.inline_cap;
+        std::vector<document_data::object_index> indexes(d.indexes.capacity() > d.indexes.size() ? d.indexes : std::vector<document_data::object_index>());
+        std::vector<std::uint32_t> index_slots(d.index_slots.capacity() > d.index_slots.size() ? d.index_slots : std::vector<std::uint32_t>());
         node* fresh = (shrink_tape && !into_header) ? static_cast<node*>(::operator new (d.tape_size * sizeof(node))) : d.inline_tape;
 
         if (shrink_tape)
@@ -1007,6 +1062,14 @@ class basic_json_document
                 d.base[1] = d.arena.data();
             }
         }
+        if (d.indexes.capacity() > d.indexes.size())
+        {
+            d.indexes.swap(indexes);
+        }
+        if (d.index_slots.capacity() > d.index_slots.size())
+        {
+            d.index_slots.swap(index_slots);
+        }
     }
 
     ////////////
@@ -1097,7 +1160,9 @@ class basic_json_document
 
     /// set the value at a JSON pointer: its parent must exist; an object
     /// member is set (added if missing), an array element assigned, and "-"
-    /// or the size of the array appends
+    /// or the size of the array appends. A null parent becomes what
+    /// basic_json's operator[](json_pointer) makes of it: an array for "-"
+    /// and for digits (padded with nulls up to the index), an object otherwise.
     template<typename V>
     view_type set(const json_pointer& ptr, V&& value)
     {
@@ -1107,6 +1172,31 @@ class basic_json_document
         }
         const view_type parent = root().at(ptr.parent_pointer());
         const auto& token = ptr.back();
+        if (parent.is_null())
+        {
+            const bool digits = std::all_of(token.begin(), token.end(), [](const char c)
+            {
+                return c >= '0' && c <= '9';
+            });
+            if (token == "-")
+            {
+                return push_back(parent, std::forward<V>(value));
+            }
+            if (digits)
+            {
+                // (an invalid index is an error before the parent changes)
+                const std::size_t idx = pointer_index(token);
+                if (idx >= 0xFFFFFFFFu)
+                {
+                    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)
+                {
+                    push_back(parent, nullptr);
+                }
+                return push_back(parent, std::forward<V>(value));
+            }
+        }
         if (parent.is_array())
         {
             const std::size_t idx = token == "-" ? parent.size() : pointer_index(token);
@@ -1254,9 +1344,9 @@ class basic_json_document
         d.discarded = true;
         detail::view::parse_failure failure;
         bool ok = false;
-        if (NLOHMANN_VIEW_UNLIKELY(size >= 0xFFFFFFF0u))
+        if (NLOHMANN_VIEW_UNLIKELY(size > detail::view::max_input_size))
         {
-            failure.code = detail::view::error_code::input_too_large; // LCOV_EXCL_LINE (4 GiB)
+            failure.code = detail::view::error_code::input_too_large;
         }
         else
         {
@@ -1268,9 +1358,11 @@ class basic_json_document
             d.base[1] = d.arena.data();
             d.arena_size = d.arena.size();
             detail::view::build_object_indexes(d);
+            std::vector<std::uint32_t>().swap(d.large_objects); // (only needed while parsing)
             d.discarded = false;
             return;
         }
+        std::vector<std::uint32_t>().swap(d.large_objects);
         if (allow_exceptions)
         {
             detail::view::throw_parse_failure<BasicJsonType>(failure, src, size, comments, trailing_commas);

single_include/nlohmann/json.hpp

@@ -7544,10 +7544,11 @@ namespace detail
 {
 
 /*!
-@brief the configuration macros that change the library's behavior
+@brief the configuration macros that json_view.hpp reads
 
 json.hpp undefines these macros at its end (see macro_unscope.hpp), so code
-that builds on the library after it (json_view.hpp) reads them here. Like the
+that builds on the library after it (json_view.hpp) reads them here. A macro
+is added when the view starts to depend on it. Like the
 macros, they are part of the ABI namespace, so they always match the
 basic_json they are used with.
 */
@@ -7555,8 +7556,6 @@ struct abi_config
 {
     /// JSON_STRICT_NUL_HANDLING: a null byte is an error, not the end of input
     static constexpr bool strict_nul_handling = JSON_STRICT_NUL_HANDLING != 0;
-    /// JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
-    static constexpr bool legacy_discarded_value_comparison = JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON != 0;
 };
 
 }  // namespace detail
@@ -8863,8 +8862,9 @@ NLOHMANN_JSON_NAMESPACE_END
 
 
 #include <cstdint> // uint64_t
-#if !defined(__SIZEOF_INT128__) && defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
-    #include <intrin0.h> // __umulh, _umul128
+#include <cstring> // memcpy
+#if defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64)) && (!defined(__SIZEOF_INT128__) || (!defined(__GNUC__) && !defined(__clang__)))
+    #include <intrin0.h> // __umulh, _umul128, _BitScanForward64, _BitScanReverse64
 #endif
 
 // #include <nlohmann/detail/macro_scope.hpp>
@@ -8883,6 +8883,10 @@ inline int count_leading_zeros(std::uint64_t x) noexcept
 {
 #if defined(__GNUC__) || defined(__clang__)
     return __builtin_clzll(x);
+#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
+    unsigned long index = 0;
+    _BitScanReverse64(&index, x);
+    return 63 - static_cast<int>(index);
 #else
     int n = 0;
     for (int shift = 32; shift != 0; shift >>= 1)
@@ -8902,6 +8906,10 @@ inline int count_trailing_zeros(std::uint64_t x) noexcept
 {
 #if defined(__GNUC__) || defined(__clang__)
     return __builtin_ctzll(x);
+#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
+    unsigned long index = 0;
+    _BitScanForward64(&index, x);
+    return static_cast<int>(index);
 #else
     int n = 0;
     for (int shift = 32; shift != 0; shift >>= 1)
@@ -8949,15 +8957,21 @@ inline uint128_parts full_multiplication(std::uint64_t a, std::uint64_t b) noexc
 #endif
 }
 
-/// eight bytes as a little-endian word (compilers fold this into one load on
-/// little-endian targets; always inlined, as GCC otherwise calls it in the
-/// number loops)
+/// eight bytes as a little-endian word (a single load on little-endian
+/// targets; always inlined, as GCC otherwise calls it in the number loops)
 JSON_HEDLEY_ALWAYS_INLINE std::uint64_t read_eight_bytes(const unsigned char* b) noexcept
 {
+#if defined(_MSC_VER) || defined(__x86_64__) || defined(__i386__) || (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
+    // the byte order already matches (all MSVC targets are little-endian)
+    std::uint64_t result = 0;
+    std::memcpy(&result, b, sizeof(result));
+    return result;
+#else
     return static_cast<std::uint64_t>(b[0]) | (static_cast<std::uint64_t>(b[1]) << 8u)
            | (static_cast<std::uint64_t>(b[2]) << 16u) | (static_cast<std::uint64_t>(b[3]) << 24u)
            | (static_cast<std::uint64_t>(b[4]) << 32u) | (static_cast<std::uint64_t>(b[5]) << 40u)
            | (static_cast<std::uint64_t>(b[6]) << 48u) | (static_cast<std::uint64_t>(b[7]) << 56u);
+#endif
 }
 
 /// eight bytes as a little-endian word
@@ -25172,6 +25186,7 @@ NLOHMANN_JSON_NAMESPACE_END
 // |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 //
 // SPDX-FileCopyrightText: 2009 Florian Loitsch <https://florian.loitsch.com/>
+// SPDX-FileCopyrightText: 2025 Victor Zverovich <https://github.com/vitaut/zmij>
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT
 
@@ -25247,13 +25262,6 @@ computed from the compressed tables of Zmij beyond it.
 namespace zmij
 {
 
-/// significand * 10^exponent
-struct decimal
-{
-    std::uint64_t significand;
-    int exponent;
-};
-
 /// the compressed powers of ten of Zmij
 inline const std::array<std::uint64_t, 28>& pow10_minor() noexcept
 {
@@ -25432,18 +25440,6 @@ JSON_HEDLEY_ALWAYS_INLINE shortest_decimal to_shortest(std::uint64_t bits) noexc
     return shortest_decimal{integral, dec_exp, static_cast<unsigned char>(digit), !round_up && !round_down};
 }
 
-/// The shortest decimal in the rounding interval of a positive finite double
-/// given by its bits, as one number. The significand can end in zeros.
-inline decimal to_decimal(std::uint64_t bits) noexcept
-{
-    const shortest_decimal d = to_shortest(bits);
-    if (d.has_digit)
-    {
-        return decimal{(d.integral * 10) + d.digit, d.exponent};
-    }
-    return decimal{d.integral, d.exponent + 1};
-}
-
 }  // namespace zmij
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END
@@ -26351,88 +26347,6 @@ void grisu2(char* buf, int& len, int& decimal_exponent, FloatType value)
     grisu2(buf, len, decimal_exponent, w.minus, w.w, w.plus);
 }
 
-/*!
-@brief the shortest digits of a positive finite float (other than double): Grisu2
-*/
-template<typename FloatType>
-JSON_HEDLEY_NON_NULL(1)
-void shortest_digits(char* buf, int& len, int& decimal_exponent, FloatType value)
-{
-    grisu2(buf, len, decimal_exponent, value);
-}
-
-/*!
-@brief the shortest digits of a positive finite double: the conversion of
-Zmij (see zmij.hpp), which always finds the shortest digits that read back as
-the same value (Grisu2 does not for about one double in a thousand), and the
-closest of them if there are several
-
-v = buf * 10^decimal_exponent, as for grisu2()
-*/
-JSON_HEDLEY_NON_NULL(1)
-inline void shortest_digits(char* buf, int& len, int& decimal_exponent, double value)
-{
-    static_assert(std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53,
-                  "internal error: the conversion of Zmij needs IEEE 754 binary64 doubles");
-    JSON_ASSERT(std::isfinite(value));
-    JSON_ASSERT(value > 0);
-
-    std::uint64_t bits = 0;
-    std::memcpy(&bits, &value, sizeof(bits));
-    zmij::decimal d = zmij::to_decimal(bits);
-    // without trailing zeros (up to 16): 8, 4, 2, 1 at a time
-    while (d.significand % 100000000 == 0)
-    {
-        d.significand /= 100000000;
-        d.exponent += 8;
-    }
-    if (d.significand % 10000 == 0)
-    {
-        d.significand /= 10000;
-        d.exponent += 4;
-    }
-    if (d.significand % 100 == 0)
-    {
-        d.significand /= 100;
-        d.exponent += 2;
-    }
-    if (d.significand % 10 == 0)
-    {
-        d.significand /= 10;
-        d.exponent += 1;
-    }
-    // at most 17 digits, written from the back two at a time
-    static constexpr const char* pairs =
-        "00010203040506070809101112131415161718192021222324252627282930313233343536373839"
-        "40414243444546474849505152535455565758596061626364656667686970717273747576777879"
-        "8081828384858687888990919293949596979899";
-    std::array<char, 20> digits{};
-    std::size_t n = digits.size();
-    while (d.significand >= 100)
-    {
-        const std::uint64_t two_digits = d.significand % 100; // a variable: GCC calls a cast of the remainder useless where std::uint64_t is std::size_t
-        const auto i = static_cast<std::size_t>(two_digits) * 2;
-        d.significand /= 100;
-        n -= 2;
-        digits[n] = pairs[i];
-        digits[n + 1] = pairs[i + 1];
-    }
-    if (d.significand >= 10)
-    {
-        const auto i = static_cast<std::size_t>(d.significand) * 2;
-        n -= 2;
-        digits[n] = pairs[i];
-        digits[n + 1] = pairs[i + 1];
-    }
-    else
-    {
-        digits[--n] = static_cast<char>('0' + d.significand);
-    }
-    len = static_cast<int>(digits.size() - n);
-    std::memcpy(buf, digits.data() + n, static_cast<std::size_t>(len));
-    decimal_exponent = d.exponent;
-}
-
 /*!
 @brief appends a decimal representation of e to buf
 @return a pointer to the element following the exponent.
@@ -26877,11 +26791,30 @@ inline char* write_short_decimal(char* first, std::uint64_t digits, int exp) noe
     return write_short_decimal(first, digits, count, exp);
 }
 
-/// a positive finite float (other than double): Grisu2 and format_buffer()
+/*!
+@brief whether FloatType is an IEEE 754 binary64 type (a double, or a long double
+that has the same format, as with MSVC and on Apple's Arm CPUs)
+
+These are the types the conversion of Zmij (see zmij.hpp) is used for; all
+others (binary32, or a format the library does not know) use Grisu2.
+*/
+template<typename FloatType>
+constexpr bool has_binary64_format() noexcept
+{
+    return std::numeric_limits<FloatType>::is_iec559
+           && std::numeric_limits<FloatType>::digits == 53
+           && std::numeric_limits<FloatType>::max_exponent == 1024
+           && sizeof(FloatType) == sizeof(std::uint64_t);
+}
+
+template<typename FloatType>
+struct is_binary64 : std::integral_constant<bool, has_binary64_format<FloatType>()> {};
+
+/// a positive finite float (other than binary64): Grisu2 and format_buffer()
 template<typename FloatType>
 JSON_HEDLEY_NON_NULL(1, 2)
 JSON_HEDLEY_RETURNS_NON_NULL
-char* write_positive(char* first, const char* last, FloatType value)
+char* write_positive_grisu2(char* first, const char* last, FloatType value)
 {
     JSON_ASSERT(last - first >= std::numeric_limits<FloatType>::max_digits10);
     static_cast<void>(last); // (only used in the assertion)
@@ -26892,7 +26825,7 @@ char* write_positive(char* first, const char* last, FloatType value)
     // len is the length of the buffer, i.e., the number of decimal digits.
     int len = 0;
     int decimal_exponent = 0;
-    shortest_digits(first, len, decimal_exponent, value);
+    grisu2(first, len, decimal_exponent, value);
 
     JSON_ASSERT(len <= std::numeric_limits<FloatType>::max_digits10);
 
@@ -26908,15 +26841,16 @@ char* write_positive(char* first, const char* last, FloatType value)
     return format_buffer(first, len, decimal_exponent, kMinExp, kMaxExp);
 }
 
-/// a positive finite double: the shortest digits (Zmij), laid out by
+/// a positive finite binary64 number: the shortest digits (Zmij), laid out by
 /// write_shortest() (through a local buffer if [first, last) is shorter than
 /// the 41 bytes it may write)
+template<typename FloatType>
 JSON_HEDLEY_NON_NULL(1, 2)
 JSON_HEDLEY_RETURNS_NON_NULL
-inline char* write_positive(char* first, const char* last, double value)
+char* write_positive_zmij(char* first, const char* last, FloatType value)
 {
-    static_assert(std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53,
-                  "internal error: the conversion of Zmij needs IEEE 754 binary64 doubles");
+    static_assert(is_binary64<FloatType>::value,
+                  "internal error: the conversion of Zmij needs IEEE 754 binary64 numbers");
     std::uint64_t bits = 0;
     std::memcpy(&bits, &value, sizeof(bits));
     const zmij::shortest_decimal d = zmij::to_shortest(bits);
@@ -26931,6 +26865,34 @@ inline char* write_positive(char* first, const char* last, double value)
     return first + len;
 }
 
+/// a positive finite binary64 number: Zmij (as a long double has the format of
+/// a double here, its bits are those of the double of the same value)
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
+char* write_positive(char* first, const char* last, FloatType value, std::true_type /*is_binary64*/)
+{
+    return write_positive_zmij(first, last, value);
+}
+
+/// a positive finite float of any other format: Grisu2
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
+char* write_positive(char* first, const char* last, FloatType value, std::false_type /*is_binary64*/)
+{
+    return write_positive_grisu2(first, last, value);
+}
+
+/// a positive finite float: Zmij for binary64 numbers, Grisu2 otherwise
+template<typename FloatType>
+JSON_HEDLEY_NON_NULL(1, 2)
+JSON_HEDLEY_RETURNS_NON_NULL
+char* write_positive(char* first, const char* last, FloatType value)
+{
+    return write_positive(first, last, value, is_binary64<FloatType> {});
+}
+
 }  // namespace dtoa_impl
 
 /*!

tests/fuzzing.md

@@ -6,7 +6,10 @@ Each parser of the library (JSON, BJData, BON8, BSON, CBOR, MessagePack, and UBJ
 Additionally, `parse_json_view_fuzzer` (`tests/src/fuzzer-parse_json_view.cpp`) cross-checks `json_document`/`json_view`
 (the zero-copy, read-only view declared in `json_view.hpp`) against `basic_json` on the same JSON text: it asserts that
 `json_document::accept` agrees with `json::accept`, that an accepted input materializes to the same value `json::parse`
-produces, and that a rejected input makes both parsers throw with an identical `what()`. It takes plain JSON text, so it
+produces, and that a rejected input makes both parsers throw with an identical `what()`. It checks this for a
+`std::string` input (borrowed, with a NUL after the last byte) and for an exact-size `std::vector<std::uint8_t>`
+(borrowed, with nothing after the last byte), and for the `ignore_comments` and `ignore_trailing_commas` options, which
+are taken from the low bits of the first input byte (the byte stays part of the text). It takes plain JSON text, so it
 reuses the `corpus_json` corpus rather than a format of its own.
 
 `json_view_image_fuzzer` (`tests/src/fuzzer-json_view_image.cpp`) tests the images of `json_document` (`save()` and

tests/src/fuzzer-parse_json_view.cpp

@@ -9,7 +9,9 @@
 /*
 This file implements a parser test suitable for fuzz testing. It checks that
 json_document (the zero-copy, read-only view of a parsed JSON text declared in
-json_view.hpp) agrees with basic_json on every input:
+json_view.hpp) agrees with basic_json on every input, for the parse options
+selected by the low bits of the first input byte (bit 0: ignore_comments, bit 1:
+ignore_trailing_commas; the byte stays part of the text):
 
 - json_document::accept(data) must equal json::accept(data)
 - if the input is accepted, json_document::parse(data).root().materialize()
@@ -18,12 +20,20 @@ json_view.hpp) agrees with basic_json on every input:
   enabled) must throw a json::parse_error or json::out_of_range whose what()
   is identical to the one json::parse(data) throws
 
+This is checked for two kinds of input: a std::string, which the document
+borrows and which ends in the NUL the parser uses as sentinel, and an
+exact-size byte vector, which has no NUL after its last byte and takes the
+parser's bounds-checked path (AddressSanitizer reports any read past the end).
+
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
 #include <cassert>
+#include <cstddef>
+#include <cstdint>
 #include <string>
+#include <vector>
 #include <nlohmann/json.hpp>
 #include <nlohmann/json_view.hpp>
 
@@ -35,65 +45,110 @@ drivers.
 using json = nlohmann::json;
 using json_document = nlohmann::json_document;
 
-// see http://llvm.org/docs/LibFuzzer.html
-extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+namespace
 {
-    // json_document::accept only has a single-argument overload; wrap the raw
-    // bytes in a (borrowed) std::string so the same bytes can be handed to it
-    const std::string input(reinterpret_cast<const char*>(data), size); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+// what json::parse does with a text: the value, or the message of the exception
+struct reference_result
+{
+    bool accepted = false;
+    json value{};
+    std::string what{}; // NOLINT(readability-redundant-member-init)
+};
 
-    const bool accepted_by_json = json::accept(data, data + size);
-    const bool accepted_by_view = json_document::accept(input);
+reference_result parse_reference(const std::uint8_t* data, std::size_t size, bool comments, bool trailing_commas)
+{
+    reference_result r;
+    r.accepted = json::accept(data, data + size, comments, trailing_commas);
+    bool json_threw = false;
+    try
+    {
+        r.value = json::parse(data, data + size, nullptr, true, comments, trailing_commas);
+    }
+    catch (const json::parse_error& e)
+    {
+        r.what = e.what();
+        json_threw = true;
+    }
+    catch (const json::out_of_range& e)
+    {
+        r.what = e.what();
+        json_threw = true;
+    }
+    // json::accept and json::parse must agree
+    assert(json_threw == !r.accepted);
+    static_cast<void>(json_threw);
+    return r;
+}
 
+// json_document must agree with the reference for this input (a container
+// that json_document::parse borrows)
+template<typename Input>
+void check_input(const Input& input, const reference_result& expected, bool comments, bool trailing_commas)
+{
     // json_document::accept must agree with json::accept on every input
-    assert(accepted_by_json == accepted_by_view);
+    const bool accepted_by_view = json_document::accept(input, comments, trailing_commas);
+    assert(expected.accepted == accepted_by_view);
+    static_cast<void>(accepted_by_view);
 
-    if (accepted_by_json)
+    if (expected.accepted)
     {
         // both parsers must agree on the resulting value
-        json const j1 = json::parse(data, data + size);
-        json_document const doc = json_document::parse(input);
+        json_document const doc = json_document::parse(input, true, comments, trailing_commas);
+        assert(!doc.is_discarded());
         json const j2 = doc.root().materialize();
-        assert(j1 == j2);
+        assert(expected.value == j2);
+        static_cast<void>(j2);
+
+        // (without exceptions, the same document)
+        json_document const quiet = json_document::parse(input, false, comments, trailing_commas);
+        assert(!quiet.is_discarded());
+        assert(quiet.node_count() == doc.node_count());
     }
     else
     {
         // both parsers must reject the input the same way when exceptions are used
-        std::string expected_what;
-        bool json_threw = false;
-        try
-        {
-            static_cast<void>(json::parse(data, data + size));
-        }
-        catch (const json::parse_error& e)
-        {
-            expected_what = e.what();
-            json_threw = true;
-        }
-        catch (const json::out_of_range& e)
-        {
-            expected_what = e.what();
-            json_threw = true;
-        }
-        assert(json_threw);
-
         bool view_threw = false;
         try
         {
-            static_cast<void>(json_document::parse(input));
+            static_cast<void>(json_document::parse(input, true, comments, trailing_commas));
         }
         catch (const json::parse_error& e)
         {
-            assert(e.what() == expected_what);
+            assert(e.what() == expected.what);
             view_threw = true;
         }
         catch (const json::out_of_range& e)
         {
-            assert(e.what() == expected_what);
+            assert(e.what() == expected.what);
             view_threw = true;
         }
         assert(view_threw);
+        static_cast<void>(view_threw);
+
+        // and without exceptions, the document is discarded
+        json_document const quiet = json_document::parse(input, false, comments, trailing_commas);
+        assert(quiet.is_discarded());
+        static_cast<void>(quiet);
     }
+}
+} // namespace
+
+// see http://llvm.org/docs/LibFuzzer.html
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+{
+    // the parse options are taken from the low bits of the first byte
+    const bool comments = size > 0 && (data[0] & 1U) != 0;
+    const bool trailing_commas = size > 0 && (data[0] & 2U) != 0;
+
+    const reference_result expected = parse_reference(data, size, comments, trailing_commas);
+
+    // a std::string: borrowed, with the NUL of std::string as sentinel
+    const std::string input(reinterpret_cast<const char*>(data), size); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    check_input(input, expected, comments, trailing_commas);
+
+    // an exact-size byte vector: borrowed, with nothing after its last byte
+    const std::vector<std::uint8_t> exact(data, data + size);
+    check_input(exact, expected, comments, trailing_commas);
 
     // return 0 - non-zero return values are reserved for future use
     return 0;

tests/src/unit-class_lexer.cpp

@@ -1792,4 +1792,11 @@ TEST_CASE("string scanning kernels")
         CHECK(nlohmann::detail::count_trailing_zeros(bit) == k);
         CHECK(nlohmann::detail::count_trailing_zeros(bit | (bit << 1u) | 0x8000000000000000u) == k);
     }
+
+    // eight bytes as a little-endian word, at any alignment
+    const unsigned char bytes[16] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF};
+    CHECK(nlohmann::detail::read_eight_bytes(bytes) == 0x0807060504030201u);
+    CHECK(nlohmann::detail::read_eight_bytes(bytes + 1) == 0x0908070605040302u);
+    CHECK(nlohmann::detail::read_eight_bytes(bytes + 8) == 0xFF0F0E0D0C0B0A09u);
+    CHECK(nlohmann::detail::read_eight_bytes(reinterpret_cast<const char*>(bytes) + 3) == 0x0B0A090807060504u);
 }

tests/src/unit-json_view.cpp

@@ -19,16 +19,19 @@ using nlohmann::ordered_json_view;
 #include <algorithm>
 #include <array>
 #include <cmath>
+#include <cstddef>
 #include <cstdint>
 #include <cstdio>
 #include <cstring>
 #include <iomanip>
 #include <iterator>
+#include <limits>
 #include <list>
 #include <map>
 #include <random>
 #include <sstream>
 #include <string>
+#include <type_traits>
 #include <unordered_map>
 #include <utility>
 #include <vector>
@@ -39,6 +42,55 @@ using nlohmann::ordered_json_view;
 
 namespace
 {
+// the value of a text, through a named document: the views of a temporary
+// document would dangle (root() of an rvalue document does not compile)
+template<typename Document, typename... Args>
+auto materialized(Args&& ... args) -> decltype(std::declval<typename Document::view_type>().materialize())
+{
+    const Document d = Document::parse(std::forward<Args>(args)...);
+    return d.root().materialize();
+}
+
+template<typename Document, typename Input>
+auto materialized_copy(Input&& input) -> decltype(std::declval<typename Document::view_type>().materialize())
+{
+    const Document d = Document::parse_copy(std::forward<Input>(input));
+    return d.root().materialize();
+}
+
+// a "byte container" that claims to hold `size` bytes, to reach the limit on
+// the size of the input without allocating gigabytes; nothing past the first
+// bytes is ever read, because the size is checked before the parse starts
+struct oversized_input
+{
+    using value_type = char;
+    std::size_t claimed;
+
+    const char* data() const
+    {
+        return "[1]";
+    }
+
+    std::size_t size() const
+    {
+        return claimed;
+    }
+};
+
+// detection of calls that must not compile
+template<typename... Args>
+using parse_call_t = decltype(json_document::parse(std::declval<Args>()...));
+template<typename... Args>
+using parse_copy_call_t = decltype(json_document::parse_copy(std::declval<Args>()...));
+template<typename... Args>
+using accept_call_t = decltype(json_document::accept(std::declval<Args>()...));
+template<typename... Args>
+using read_call_t = decltype(std::declval<json_document&>().read(std::declval<Args>()...));
+template<typename Document>
+using root_call_t = decltype(std::declval<Document>().root());
+template<typename View>
+using bool_conversion_t = decltype(static_cast<bool>(std::declval<View>()));
+
 #if !defined(JSON_NOEXCEPTION)
 // the exception parse() throws for a text, or "" if it accepts it
 std::string parse_exception(const std::string& text, bool comments = false, bool trailing_commas = false)
@@ -152,7 +204,6 @@ TEST_CASE("json_view")
             CHECK(v.is_primitive() == j.is_primitive());
             CHECK(v.is_structured() == j.is_structured());
             CHECK(!v.is_discarded());
-            CHECK(static_cast<bool>(v));
             CHECK(v.size() == j.size());
             CHECK(v.empty() == j.empty());
             CHECK(v.materialize() == j);
@@ -160,7 +211,6 @@ TEST_CASE("json_view")
 
         const json_view invalid{};
         CHECK(invalid.is_discarded());
-        CHECK(!static_cast<bool>(invalid));
         CHECK(invalid.type() == json::value_t::discarded);
         CHECK(invalid.size() == 0);
         CHECK(invalid.empty());
@@ -176,19 +226,19 @@ TEST_CASE("json_view")
             std::string text;
             g.value(text, 0);
             CAPTURE(text)
-            CHECK(json_document::parse(text).root().materialize() == json::parse(text));
+            CHECK(materialized<json_document>(text) == json::parse(text));
             // member order as ordered_json::parse keeps it
-            CHECK(ordered_json_document::parse(text).root().materialize().dump() == ordered_json::parse(text).dump());
+            CHECK(materialized<ordered_json_document>(text).dump() == ordered_json::parse(text).dump());
         }
         // duplicate keys: the last value, at the position of the first key
-        CHECK(json_document::parse(R"({"a":1,"b":2,"a":3})").root().materialize() == json::parse(R"({"a":1,"b":2,"a":3})"));
-        CHECK(ordered_json_document::parse(R"({"a":1,"b":2,"a":3})").root().materialize().dump() == R"({"a":3,"b":2})");
+        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})");
         // very deep nesting (iterative, as parse())
         const std::string deep = std::string(100000, '[') + std::string(100000, ']');
-        CHECK(json_document::parse(deep).root().materialize() == json::parse(deep));
+        CHECK(materialized<json_document>(deep) == json::parse(deep));
 #if JSON_DIAGNOSTICS
         // the parents are set, so errors name the path
-        const json m = json_document::parse(R"({"a":{"b":[1]}})").root().materialize();
+        const json m = materialized<json_document>(R"({"a":{"b":[1]}})");
         CHECK_THROWS_WITH_AS(m.at("a").at("b").at(0).at("x"), "[json.exception.type_error.304] (/a/b/0) cannot use at() with number", json::type_error&);
 #endif
     }
@@ -261,7 +311,7 @@ TEST_CASE("json_view")
             CHECK(json_document::accept(text));
             if (accepted)
             {
-                CHECK(float_document::parse(text).root().materialize() == json_float::parse(text));
+                CHECK(materialized<float_document>(text) == json_float::parse(text));
             }
         }
         float_document f;
@@ -275,7 +325,7 @@ TEST_CASE("json_view")
         CHECK(json_document::accept(with_nul) == json::accept(with_nul));
         const std::string nul_in_comment("[1, // c\0\n2]", 12);
         CHECK(json_document::accept(nul_in_comment, true) == json::accept(nul_in_comment, true));
-        CHECK(json_document::parse("\xEF\xBB\xBF[1]").root().materialize() == json::parse("\xEF\xBB\xBF[1]"));
+        CHECK(materialized<json_document>("\xEF\xBB\xBF[1]") == json::parse("\xEF\xBB\xBF[1]"));
 #if !defined(JSON_NOEXCEPTION)
         CHECK(view_exception("\xEF\xBB") == parse_exception("\xEF\xBB"));
 #endif
@@ -291,18 +341,18 @@ TEST_CASE("json_view")
         CHECK(!borrowed.owns_source());
         CHECK(borrowed.source().data() == text.data());
         CHECK(borrowed.root().materialize() == expected);
-        CHECK(json_document::parse(text.c_str()).root().materialize() == expected);
-        CHECK(json_document::parse(R"([1, "two", {"three": 3.5}])").root().materialize() == expected);
-        CHECK(json_document::parse(text.data(), text.data() + text.size()).root().materialize() == expected);
+        CHECK(materialized<json_document>(text.c_str()) == expected);
+        CHECK(materialized<json_document>(R"([1, "two", {"three": 3.5}])") == expected);
+        CHECK(materialized<json_document>(text.data(), text.data() + text.size()) == expected);
         const std::vector<char> chars(text.begin(), text.end());
         CHECK(!json_document::parse(chars).owns_source());
-        CHECK(json_document::parse(chars).root().materialize() == expected);
+        CHECK(materialized<json_document>(chars) == expected);
         const std::vector<std::uint8_t> bytes(text.begin(), text.end());
-        CHECK(json_document::parse(bytes).root().materialize() == expected);
+        CHECK(materialized<json_document>(bytes) == expected);
 #ifdef JSON_HAS_CPP_17
         const std::string_view sv = text;
         CHECK(!json_document::parse(sv).owns_source());
-        CHECK(json_document::parse(sv).root().materialize() == expected);
+        CHECK(materialized<json_document>(sv) == expected);
 #endif
 
         // owned
@@ -311,15 +361,28 @@ TEST_CASE("json_view")
         CHECK(from_rvalue.owns_source());
         CHECK(from_rvalue.root().materialize() == expected);
         CHECK(json_document::parse(std::vector<char>(text.begin(), text.end())).owns_source());
+        // a const rvalue cannot be moved from, and is not borrowed (it may be a
+        // temporary): it is copied, as is a const rvalue of any container
+        const std::string const_text = text;
+        const json_document from_const_rvalue = json_document::parse(std::move(const_text)); // NOLINT(performance-move-const-arg,hicpp-move-const-arg)
+        CHECK(from_const_rvalue.owns_source());
+        CHECK(from_const_rvalue.source().data() != const_text.data());
+        CHECK(from_const_rvalue.root().materialize() == expected);
+        json_document read_const_rvalue;
+        read_const_rvalue.read(std::move(const_text)); // NOLINT(performance-move-const-arg,hicpp-move-const-arg)
+        CHECK(read_const_rvalue.owns_source());
+        CHECK(read_const_rvalue.root().materialize() == expected);
+        const std::vector<char> const_chars(text.begin(), text.end());
+        CHECK(json_document::parse(std::move(const_chars)).owns_source()); // NOLINT(performance-move-const-arg,hicpp-move-const-arg)
         CHECK(json_document::parse_copy(text).owns_source());
-        CHECK(json_document::parse_copy(text).root().materialize() == expected);
+        CHECK(materialized_copy<json_document>(text) == expected);
         std::istringstream stream(text);
         const json_document from_stream = json_document::parse(stream);
         CHECK(from_stream.owns_source());
         CHECK(from_stream.root().materialize() == expected);
         const std::list<char> list(text.begin(), text.end());
         CHECK(json_document::parse(list.begin(), list.end()).owns_source());
-        CHECK(json_document::parse(list.begin(), list.end()).root().materialize() == expected);
+        CHECK(materialized<json_document>(list.begin(), list.end()) == expected);
 
         // iterator pairs: pointers are borrowed, and so are contiguous library
         // iterators where the input adapter detects them (C++20)
@@ -330,14 +393,85 @@ TEST_CASE("json_view")
         CHECK((from_iterators.source().data() == chars.data()) == contiguous);
         CHECK(from_iterators.root().materialize() == expected);
         const std::string padded = "x" + text + "x";
-        CHECK(json_document::parse(padded.begin() + 1, padded.end() - 1).root().materialize() == expected);
+        CHECK(materialized<json_document>(padded.begin() + 1, padded.end() - 1) == expected);
         CHECK(json_document::parse(chars.cbegin(), chars.cbegin(), false).is_discarded());
         const std::wstring wide = L"[\"\u00e4\u20ac\", 1]";
-        CHECK(json_document::parse(wide).root().materialize() == json::parse(wide));
+        CHECK(materialized<json_document>(wide) == json::parse(wide));
         CHECK(json_document::parse(static_cast<const char*>(nullptr), false).is_discarded());
         CHECK(json_document::parse("", false).is_discarded());
     }
 
+    SECTION("integer arguments do not compile")
+    {
+        using nlohmann::detail::is_detected;
+
+        // a length is not a flag: parse(ptr, len) would convert len to
+        // allow_exceptions and read ptr as a C string, which need not end
+        static_assert(is_detected<parse_call_t, const char*, bool>::value, "parse(ptr, bool) is valid");
+        static_assert(is_detected<parse_call_t, const char*, bool, bool, bool>::value, "parse(ptr, bool, bool, bool) is valid");
+        static_assert(is_detected<parse_call_t, const char*, const char*>::value, "parse(first, last) is valid");
+        static_assert(is_detected<parse_call_t, const char*, const char*, bool>::value, "parse(first, last, bool) is valid");
+        static_assert(!is_detected<parse_call_t, const char*, std::size_t>::value, "parse(ptr, len) must not compile");
+        static_assert(!is_detected<parse_call_t, const char*, int>::value, "parse(ptr, int) must not compile");
+        static_assert(!is_detected<parse_call_t, const char*, char>::value, "parse(ptr, char) must not compile");
+        static_assert(!is_detected<parse_call_t, const char*, std::size_t, bool>::value, "parse(ptr, len, bool) must not compile");
+        static_assert(!is_detected<parse_call_t, const std::string&, std::size_t>::value, "parse(string, len) must not compile");
+        static_assert(!is_detected<parse_call_t, const std::vector<char>&, std::size_t>::value, "parse(vector, len) must not compile");
+
+        static_assert(is_detected<parse_copy_call_t, const char*, bool>::value, "parse_copy(ptr, bool) is valid");
+        static_assert(!is_detected<parse_copy_call_t, const char*, std::size_t>::value, "parse_copy(ptr, len) must not compile");
+
+        static_assert(is_detected<accept_call_t, const char*, bool>::value, "accept(ptr, bool) is valid");
+        static_assert(!is_detected<accept_call_t, const char*, std::size_t>::value, "accept(ptr, len) must not compile");
+
+        static_assert(is_detected<read_call_t, const char*, bool>::value, "read(ptr, bool) is valid");
+        static_assert(!is_detected<read_call_t, const char*, std::size_t>::value, "read(ptr, len) must not compile");
+
+        // json_view has no conversion to bool: unlike basic_json's, it would
+        // mean "exists", not "is not null"; use is_discarded()
+        static_assert(!is_detected<bool_conversion_t, json_view>::value, "json_view must not convert to bool");
+
+        // the valid calls still work
+        const char* const text = "[1]";
+        CHECK(materialized<json_document>(text, true) == json::parse(text));
+        CHECK(json_document::accept(text, true, true));
+    }
+
+    SECTION("root of a temporary document does not compile")
+    {
+        using nlohmann::detail::is_detected;
+
+        // the view would dangle: auto v = json_document::parse(text).root();
+        static_assert(is_detected<root_call_t, json_document&>::value, "root() of an lvalue is valid");
+        static_assert(is_detected<root_call_t, const json_document&>::value, "root() of a const lvalue is valid");
+        static_assert(!is_detected<root_call_t, json_document>::value, "root() of an rvalue must not compile");
+        static_assert(!is_detected < root_call_t, json_document && >::value, "root() of an rvalue must not compile");
+        static_assert(!is_detected < root_call_t, const json_document && >::value, "root() of a const rvalue must not compile");
+        static_assert(!is_detected<root_call_t, ordered_json_document>::value, "root() of an rvalue must not compile");
+
+        // a named document is fine, also after a move
+        json_document d = json_document::parse("[1]");
+        CHECK(d.root().size() == 1);
+        const json_document moved = std::move(d);
+        CHECK(moved.root().size() == 1);
+    }
+
+    SECTION("input size limit")
+    {
+        // 32-bit offsets: the limit is 4 GiB minus 16 bytes (a margin below 2^32),
+        // which is what the exception message and the documentation say
+        const std::size_t limit = nlohmann::detail::view::max_input_size;
+        CHECK(limit == std::size_t{4294967279u});
+
+        const oversized_input input{limit + 1};
+        CHECK(!json_document::accept(input));
+        CHECK(json_document::parse(input, false).is_discarded());
+#if !defined(JSON_NOEXCEPTION)
+        json_document d;
+        CHECK_THROWS_WITH_AS(d = json_document::parse(input), "[json.exception.out_of_range.416] input of 4294967280 bytes or more is not supported by json_document", json::out_of_range&);
+#endif
+    }
+
     SECTION("document lifetime and reuse")
     {
         json_document d;
@@ -443,7 +577,7 @@ std::string exception_of(F f)
 
 // compares a view with the ordered_json value materialize() gives for it:
 // types, sizes, elements and members (by index, key, and iteration), in
-// document order; duplicate keys are found as their first occurrence
+// document order; duplicate keys are found as their last occurrence
 void check_access(const ordered_json_view& v, const ordered_json& j)
 {
     REQUIRE(v.type() == j.type());
@@ -460,7 +594,7 @@ void check_access(const ordered_json_view& v, const ordered_json& j)
             ++i;
         }
         CHECK(i == v.size());
-        CHECK(!v[v.size()]);
+        CHECK(v[v.size()].is_discarded());
         std::size_t index = 0;
         for (const auto& item : v.items())
         {
@@ -484,11 +618,23 @@ void check_access(const ordered_json_view& v, const ordered_json& j)
             const std::string key(it.key().data(), it.key().size());
             CHECK(v.contains(key));
             CHECK(v.count(key) == 1);
-            if (std::find(keys.begin(), keys.end(), key) != keys.end())
+            if (std::find(keys.begin(), keys.end(), key) == keys.end())
             {
-                continue; // a duplicate: lookups find the first one
+                keys.push_back(key);
+            }
+            // lookups find the last member with the key, which is this one if
+            // there is no later one
+            auto next = it;
+            ++next;
+            bool is_last = true;
+            for (; next != v.end(); ++next)
+            {
+                is_last = is_last && next.key() != it.key();
+            }
+            if (!is_last)
+            {
+                continue;
             }
-            keys.push_back(key);
             CHECK(v.find(key) == it);
             CHECK(v[key].materialize() == it->materialize());
             CHECK(v.at(key).materialize() == it.value().materialize());
@@ -514,7 +660,7 @@ void check_access(const ordered_json_view& v, const ordered_json& j)
                 CHECK(v.back().materialize() == j.back());
             }
         }
-        CHECK(!v["not a key in the generated documents"]);
+        CHECK(v["not a key in the generated documents"].is_discarded());
         CHECK(v.find("not a key in the generated documents") == v.end());
     }
     else
@@ -579,15 +725,35 @@ TEST_CASE("json_view element access and iteration")
 #endif
     }
 
-    SECTION("duplicate keys: lookups find the first member, iteration all")
+    SECTION("duplicate keys: lookups find the last member, iteration all")
     {
         const json_document d = json_document::parse(R"({"a":1,"b":2,"a":3})");
         const json_view v = d.root();
         CHECK(v.size() == 3);
-        CHECK(v["a"].materialize() == 1);
-        CHECK(v.at("a").materialize() == 1);
-        CHECK(v.find("a") == v.begin());
+        CHECK(v["a"].materialize() == 3);
+        CHECK(v.at("a").materialize() == 3);
+        CHECK(v.find("a") == std::next(v.begin(), 2));
+        CHECK(v.find("a").value().materialize() == 3);
+        CHECK(v.find("b") == std::next(v.begin()));
         CHECK(v.count("a") == 1);
+        CHECK(v.contains("a"));
+        CHECK(v.value("a", 0) == 3);
+        CHECK(v["a"].materialize() == v.materialize()["a"]); // as materialize()
+        // keys of every length class (the 16-byte short compare and memcmp)
+        for (const std::size_t n :
+                {
+                    0u, 1u, 3u, 7u, 8u, 15u, 16u, 17u, 40u
+                })
+        {
+            const std::string key(n, 'k');
+            const json_document dk = json_document::parse("{\"" + key + "\":1,\"" + key + "x\":2,\"" + key + "\":3,\"" + key + "\":4}");
+            CAPTURE(n)
+            CHECK(dk.root()[key].materialize() == 4);
+            CHECK(dk.root().at(key).materialize() == 4);
+            CHECK(dk.root().find(key) == std::next(dk.root().begin(), 3));
+            CHECK(dk.root().value(key, 0) == 4);
+            CHECK(dk.root()[key + "x"].materialize() == 2);
+        }
         std::string order;
         for (auto it = v.begin(); it != v.end(); ++it)
         {
@@ -638,14 +804,131 @@ TEST_CASE("json_view element access and iteration")
 
         // where basic_json has undefined behavior, the view answers safely
         const json_document d = json_document::parse(R"({"a":[]})");
-        CHECK(!d.root()["b"]);
-        CHECK(!d.root()["a"][0]);
+        CHECK(d.root()["b"].is_discarded());
+        CHECK(d.root()["a"][0].is_discarded());
         CHECK_THROWS_WITH_AS(d.root()["a"].front(), "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
         CHECK_THROWS_WITH_AS(d.root()["a"].back(), "[json.exception.invalid_iterator.214] cannot get value", json::invalid_iterator&);
         const json_view invalid{};
         CHECK(invalid.begin() == invalid.end());
         CHECK(std::string(invalid.type_name()) == "discarded");
-        CHECK_THROWS_WITH_AS(invalid["a"], "[json.exception.type_error.305] cannot use operator[] with a string argument with discarded", json::type_error&);
+    }
+
+    SECTION("chained access is safe: operator[] of a discarded view is discarded")
+    {
+        const json_document d = json_document::parse(R"({"a":{"b":[10,20]},"s":"str"})");
+        const json_view v = d.root();
+        // missing keys and indexes
+        CHECK(v["x"].is_discarded());
+        CHECK(v["x"]["y"].is_discarded());
+        CHECK(v["x"]["y"]["z"].is_discarded());
+        CHECK(v["x"][0].is_discarded());
+        CHECK(v["x"][0u][1L].is_discarded());
+        CHECK(v["a"]["b"][2].is_discarded());
+        CHECK(v["a"]["b"][2]["c"].is_discarded());
+        CHECK(v["a"]["b"][2][json_view::json_pointer("/c")].is_discarded());
+        CHECK(v["x"][json_view::json_pointer("/a/b")].is_discarded());
+        CHECK(v["x"][json_view::json_pointer("")].is_discarded());
+        CHECK(v["x"]["y"].is_discarded());
+        CHECK(v["x"][std::string("y")].is_discarded());
+        // a resolvable path still resolves
+        CHECK(v["a"]["b"][1].materialize() == 20);
+        CHECK(v[json_view::json_pointer("/a/b/1")].materialize() == 20);
+        // the discarded view of an unresolved pointer is discarded too
+        CHECK(v[json_view::json_pointer("/x/y")]["z"].is_discarded());
+        CHECK(v[json_view::json_pointer("/a/b/5")][0].is_discarded());
+#if !defined(JSON_NOEXCEPTION)
+        // type errors on values that are not discarded stay
+        CHECK_THROWS_WITH_AS(v[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with object", json::type_error&);
+        CHECK_THROWS_WITH_AS(v["a"]["b"]["c"], "[json.exception.type_error.305] cannot use operator[] with a string argument with array", json::type_error&);
+        CHECK_THROWS_WITH_AS(v["s"]["c"], "[json.exception.type_error.305] cannot use operator[] with a string argument with string", json::type_error&);
+        CHECK_THROWS_WITH_AS(v["s"][0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with string", json::type_error&);
+        CHECK_THROWS_AS(v["a"]["b"][0]["c"], json::type_error&);
+        CHECK_THROWS_AS(v["s"][json_view::json_pointer("/x")], json::out_of_range&);
+        // at() keeps throwing on a discarded view
+        const json_view invalid{};
+        CHECK(invalid["a"].is_discarded());
+        CHECK(invalid[0].is_discarded());
+        CHECK(invalid[json_view::json_pointer("/a")].is_discarded());
+        CHECK_THROWS_WITH_AS(invalid.at("a"), "[json.exception.type_error.304] cannot use at() with discarded", json::type_error&);
+        CHECK_THROWS_WITH_AS(invalid.at(0), "[json.exception.type_error.304] cannot use at() with discarded", json::type_error&);
+        CHECK_THROWS_AS(v.at("x").at("y"), json::out_of_range&);
+        CHECK_THROWS_AS(v["x"].at("y"), json::type_error&);
+        CHECK_THROWS_AS(v.at(json_view::json_pointer("/x/y")), json::out_of_range&);
+        CHECK_THROWS_AS(v["x"].at(json_view::json_pointer("/y")), json::out_of_range&);
+#endif
+    }
+
+    SECTION("integer types as array indexes")
+    {
+        const json_document d = json_document::parse("[10,20,30]");
+        const json_view v = d.root();
+        const json j = v.materialize();
+        // (compile-time: no overload is ambiguous)
+        CHECK(v[0].materialize() == 10);
+        CHECK(v[1].materialize() == 20);
+        CHECK(v[0u].materialize() == 10);
+        CHECK(v[1u].materialize() == 20);
+        CHECK(v[1L].materialize() == 20);
+        CHECK(v[2UL].materialize() == 30);
+        CHECK(v[1LL].materialize() == 20);
+        CHECK(v[2ULL].materialize() == 30);
+        CHECK(v[static_cast<short>(1)].materialize() == 20);
+        CHECK(v[static_cast<unsigned short>(2)].materialize() == 30);
+        CHECK(v[static_cast<signed char>(1)].materialize() == 20);
+        CHECK(v[static_cast<unsigned char>(2)].materialize() == 30);
+        CHECK(v[std::int8_t(1)].materialize() == 20);
+        CHECK(v[std::int16_t(2)].materialize() == 30);
+        CHECK(v[std::int32_t(1)].materialize() == 20);
+        CHECK(v[std::int64_t(2)].materialize() == 30);
+        CHECK(v[std::uint32_t(0)].materialize() == 10);
+        CHECK(v[std::uint64_t(1)].materialize() == 20);
+        CHECK(v[std::size_t(2)].materialize() == 30);
+        CHECK(v[std::ptrdiff_t(1)].materialize() == 20);
+        CHECK(j[0u] == 10); // as basic_json
+
+        CHECK(v.at(0).materialize() == 10);
+        CHECK(v.at(1u).materialize() == 20);
+        CHECK(v.at(1L).materialize() == 20);
+        CHECK(v.at(2LL).materialize() == 30);
+        CHECK(v.at(2ULL).materialize() == 30);
+        CHECK(v.at(static_cast<short>(1)).materialize() == 20);
+        CHECK(v.at(static_cast<unsigned short>(2)).materialize() == 30);
+        CHECK(v.at(std::int32_t(0)).materialize() == 10);
+        CHECK(v.at(std::uint32_t(0)).materialize() == 10);
+        CHECK(v.at(std::int64_t(0)).materialize() == 10);
+        CHECK(v.at(std::uint64_t(1)).materialize() == 20);
+        CHECK(v.at(std::size_t(2)).materialize() == 30);
+        CHECK(j.at(std::uint32_t(0)) == 10); // as basic_json
+
+        // out of range, including negative values (no wrap-around)
+        CHECK(v[3].is_discarded());
+        CHECK(v[3u].is_discarded());
+        CHECK(v[3L].is_discarded());
+        CHECK(v[-1].is_discarded());
+        CHECK(v[-1L].is_discarded());
+        CHECK(v[-1LL].is_discarded());
+        CHECK(v[static_cast<short>(-1)].is_discarded());
+        CHECK(v[std::int64_t(-3)].is_discarded());
+        CHECK(v[(std::numeric_limits<std::int64_t>::min)()].is_discarded());
+        CHECK(v[(std::numeric_limits<std::uint64_t>::max)()].is_discarded());
+        CHECK(v[(std::numeric_limits<std::size_t>::max)()].is_discarded());
+        CHECK(v[std::numeric_limits<int>::max()].is_discarded());
+#if !defined(JSON_NOEXCEPTION)
+        CHECK_THROWS_WITH_AS(v.at(3), "[json.exception.out_of_range.401] array index 3 is out of range", json::out_of_range&);
+        CHECK_THROWS_WITH_AS(v.at(3u), "[json.exception.out_of_range.401] array index 3 is out of range", json::out_of_range&);
+        CHECK_THROWS_WITH_AS(v.at(std::int64_t(3)), "[json.exception.out_of_range.401] array index 3 is out of range", json::out_of_range&);
+        CHECK_THROWS_AS(v.at(-1), json::out_of_range&);
+        CHECK_THROWS_AS(v.at(-1L), json::out_of_range&);
+        CHECK_THROWS_AS(v.at(std::int64_t(-1)), json::out_of_range&);
+        CHECK_THROWS_AS(v.at((std::numeric_limits<std::int64_t>::min)()), json::out_of_range&);
+        CHECK_THROWS_AS(v.at((std::numeric_limits<std::uint64_t>::max)()), json::out_of_range&);
+        // not an array
+        const json_document o = json_document::parse("{}");
+        CHECK_THROWS_AS(o.root()[0u], json::type_error&);
+        CHECK_THROWS_AS(o.root()[1L], json::type_error&);
+        CHECK_THROWS_AS(o.root().at(std::uint32_t(0)), json::type_error&);
+        CHECK_THROWS_AS(o.root().at(std::int64_t(0)), json::type_error&);
+#endif
     }
 
     SECTION("iterators")
@@ -919,10 +1202,12 @@ TEST_CASE("json_view values")
             CAPTURE(token)
             const std::string text = "[" + token + "]";
             const double b = json::parse(text)[0].get<double>();
-            CHECK(bits(json_document::parse(text).root()[0].get<double>()) == bits(b));
+            const json_document dd = json_document::parse(text);
+            CHECK(bits(dd.root()[0].get<double>()) == bits(b));
             if (std::abs(b) < 1e38)
             {
-                CHECK(bits(nlohmann::basic_json_document<json_float>::parse(text).root()[0].get<float>()) == bits(json_float::parse(text)[0].get<float>()));
+                const nlohmann::basic_json_document<json_float> df = nlohmann::basic_json_document<json_float>::parse(text);
+                CHECK(bits(df.root()[0].get<float>()) == bits(json_float::parse(text)[0].get<float>()));
             }
         }
     }
@@ -979,7 +1264,8 @@ TEST_CASE("json_view values")
         CHECK(count == 3);
 
         // a duplicate key: the last value, as parse()
-        CHECK((json_document::parse(R"({"a":1,"a":2})").root().get<std::map<std::string, int>>() == std::map<std::string, int> {{"a", 2}}));
+        const json_document dup = json_document::parse(R"({"a":1,"a":2})");
+        CHECK((dup.root().get<std::map<std::string, int>>() == std::map<std::string, int> {{"a", 2}}));
 
         const json_view invalid{};
         CHECK_THROWS_WITH_AS(invalid.get<int>(), "[json.exception.type_error.302] type must be number, but is discarded", json::type_error&);
@@ -1070,7 +1356,7 @@ TEST_CASE("json_view JSON pointers")
             else if (at_error.find("out_of_range.401") != std::string::npos || at_error.find("out_of_range.403") != std::string::npos) // NOLINT(abseil-string-find-str-contains)
             {
                 // undefined behavior for const basic_json::operator[]
-                CHECK(!v[p]);
+                CHECK(v[p].is_discarded());
             }
             else
             {
@@ -1198,7 +1484,8 @@ TEST_CASE("json_view dump")
                 many_tokens += (i != 0 ? "," : "") + token;
             }
             many_tokens += ']';
-            CHECK(json_document::parse(many_tokens).root().dump() == json::parse(many_tokens).dump());
+            const json_document many_doc = json_document::parse(many_tokens);
+            CHECK(many_doc.root().dump() == json::parse(many_tokens).dump());
         }
 
         // random doubles, written as parse() and dump() would
@@ -1215,10 +1502,12 @@ TEST_CASE("json_view dump")
             }
         }
         many += ']';
-        CHECK(json_document::parse(many).root().dump() == json::parse(many).dump());
+        const json_document many_document = json_document::parse(many);
+        CHECK(many_document.root().dump() == json::parse(many).dump());
 
         using json_float = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
-        CHECK(nlohmann::basic_json_document<json_float>::parse("[0.1, 1.5e10, 3.4028235e38]").root().dump() == json_float::parse("[0.1, 1.5e10, 3.4028235e38]").dump());
+        const nlohmann::basic_json_document<json_float> float_document = nlohmann::basic_json_document<json_float>::parse("[0.1, 1.5e10, 3.4028235e38]");
+        CHECK(float_document.root().dump() == json_float::parse("[0.1, 1.5e10, 3.4028235e38]").dump());
     }
 
     SECTION("members in document order, all of them")
@@ -1231,7 +1520,42 @@ TEST_CASE("json_view dump")
     SECTION("deep nesting")
     {
         const std::string deep = std::string(100000, '[') + std::string(100000, ']');
-        CHECK(json_document::parse(deep).root().dump() == deep);
+        const json_document deep_document = json_document::parse(deep);
+        CHECK(deep_document.root().dump() == deep);
+    }
+
+    SECTION("the output buffer of a small value is small")
+    {
+        // an escaped key after the value: its node lies in the arena, so the
+        // source extent of the value cannot be read from the next node
+        const std::string big(100000, 'a');
+        const std::string text = R"({"small":1,"list":[1,2,3],"k\n":")" + big + R"("})";
+        const json_document d = json_document::parse(text);
+        const auto small = d.root()["small"].dump();
+        CHECK(small == "1");
+        CHECK(small.capacity() < 4096);
+        const auto list = d.root()["list"].dump();
+        CHECK(list == "[1,2,3]");
+        CHECK(list.capacity() < 4096);
+        CHECK(d.root()["list"].dump(2).capacity() < 4096);
+
+        // the whole document and the large value are unaffected
+        CHECK(d.root().dump() == ordered_json::parse(text).dump());
+        CHECK(d.root()["k\n"].dump() == "\"" + big + "\"");
+    }
+
+    SECTION("output that outgrows the estimate")
+    {
+        // ensure_ascii writes six bytes for each two-byte character
+        std::string chars;
+        for (int i = 0; i < 5000; ++i)
+        {
+            chars += "\xC3\xA9";
+        }
+        const json_document d = json_document::parse("{\"a\":\"" + chars + R"(","k\n":1})");
+        const json expected = json::parse("\"" + chars + "\"");
+        CHECK(d.root()["a"].dump(-1, ' ', true) == expected.dump(-1, ' ', true));
+        CHECK(d.root()["a"].dump(-1, ' ', true).size() == 2 + 5000 * 6);
     }
 
     SECTION("streams and discarded views")
@@ -1293,7 +1617,9 @@ TEST_CASE("json_view comparison")
     {
         const auto same = [](const char* x, const char* y)
         {
-            return json_document::parse(x).root() == json_document::parse(y).root();
+            const json_document dx = json_document::parse(x);
+            const json_document dy = json_document::parse(y);
+            return dx.root() == dy.root();
         };
         CHECK(same("1", "1.0"));
         CHECK(same("[1, -1, 2.5]", "[1.0, -1.0, 25e-1]"));
@@ -1308,15 +1634,20 @@ TEST_CASE("json_view comparison")
         CHECK(same("\"\\u00e9\"", "\"\xc3\xa9\""));
         CHECK(!same("null", "false"));
         CHECK(!same("[]", "{}"));
-        CHECK(ordered_json_document::parse(R"({"a": 1, "b": 2, "a": 3})").root() == ordered_json_document::parse(R"({"a": 3, "b": 2})").root());
-        CHECK(ordered_json_document::parse(R"({"a": 1, "b": 2})").root() != ordered_json_document::parse(R"({"b": 2, "a": 1})").root());
+        const ordered_json_document dup = ordered_json_document::parse(R"({"a": 1, "b": 2, "a": 3})");
+        const ordered_json_document last = ordered_json_document::parse(R"({"a": 3, "b": 2})");
+        CHECK(dup.root() == last.root());
+        const ordered_json_document ab = ordered_json_document::parse(R"({"a": 1, "b": 2})");
+        const ordered_json_document ba = ordered_json_document::parse(R"({"b": 2, "a": 1})");
+        CHECK(ab.root() != ba.root());
 
         // discarded values compare as basic_json's do
         const json discarded(json::value_t::discarded);
         CHECK((json_view() == json_view()) == (discarded == discarded)); // NOLINT(readability-container-size-empty): operator== is tested
         CHECK((json_view() == discarded) == (discarded == discarded));
-        CHECK(!(json_view() == json_document::parse("null").root())); // NOLINT(readability-container-size-empty)
-        CHECK(!(json_document::parse("null").root() == discarded));
+        const json_document null_document = json_document::parse("null");
+        CHECK(!(json_view() == null_document.root())); // NOLINT(readability-container-size-empty)
+        CHECK(!(null_document.root() == discarded));
     }
 
     SECTION("deep nesting")
@@ -1327,7 +1658,8 @@ TEST_CASE("json_view comparison")
         CHECK(a.root() == b.root());
         CHECK(a.root() == json::parse(deep));
         const std::string other = std::string(100000, '[') + "1" + std::string(100000, ']');
-        CHECK(a.root() != json_document::parse(other).root());
+        const json_document c = json_document::parse(other);
+        CHECK(a.root() != c.root());
     }
 }
 
@@ -1352,20 +1684,223 @@ TEST_CASE("json_view large objects")
         for (std::size_t i = 0; i < members; ++i)
         {
             const std::string key = std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\n" : "");
-            CHECK(v[key].get<std::size_t>() == i);
             CHECK(v.contains(key));
             CHECK(v.find(key).key() == key);
-            CHECK(v.at(key).get<std::size_t>() == i);
             CHECK(!v.contains(key + "x"));
+            if (key == "k1")
+            {
+                continue; // repeated below: the last member wins
+            }
+            CHECK(v[key].get<std::size_t>() == i);
+            CHECK(v.at(key).get<std::size_t>() == i);
         }
         CHECK(v[""].get_string() == "empty key");
-        CHECK(v["k1"].get<int>() == 1); // the first of duplicate keys, as for small objects
+        CHECK(v["k1"].get_string() == "a duplicate of an earlier key"); // the last of duplicate keys, as for small objects
+        CHECK(v.at("k1").get_string() == "a duplicate of an earlier key");
         CHECK(!v.contains("missing"));
         CHECK_THROWS_WITH_AS(v.at("missing"), "[json.exception.out_of_range.403] key 'missing' not found", json::out_of_range&);
         CHECK(v == j);
         CHECK(v.materialize() == j);
     }
 
+    SECTION("duplicate keys: the last member wins, with and without a table")
+    {
+        // an object of `total` members: the keys "k0".."k<n-1>" in order, then
+        // three keys repeated twice more (one copy in the middle, one at the
+        // end), and two keys repeated once; the value of a member is its
+        // position, so that the last member of a key can be told apart
+        struct member
+        {
+            std::string key;
+            std::size_t position;
+        };
+        const auto make_members = [](std::size_t total)
+        {
+            std::vector<std::string> keys;
+            for (std::size_t i = 0; i + 8 < total; ++i)
+            {
+                keys.push_back("k" + std::to_string(i));
+            }
+            const std::size_t n = keys.size();
+            const std::array<std::size_t, 3> triple = {{3, 17, n - 1}};
+            const std::array<std::size_t, 2> twice = {{5, n / 2}};
+            std::vector<std::string> ordered = keys;
+            for (const std::size_t i : triple)
+            {
+                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 2), keys[i]);
+            }
+            for (const std::size_t i : twice)
+            {
+                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 3), keys[i]);
+            }
+            for (const std::size_t i : triple)
+            {
+                ordered.push_back(keys[i]);
+            }
+            std::vector<member> result;
+            for (std::size_t i = 0; i < ordered.size(); ++i)
+            {
+                result.push_back({ordered[i], i});
+            }
+            return result;
+        };
+
+        // 100 and 127 members: no table; 128 members and more: a table
+        for (const std::size_t total :
+                {
+                    100u, 127u, 128u, 200u, 5000u
+                })
+        {
+            CAPTURE(total)
+            const std::vector<member> members = make_members(total);
+            REQUIRE(members.size() >= total);
+            REQUIRE(members.size() >= 100);
+            std::string text = "{";
+            std::map<std::string, std::size_t> last;
+            for (const member& m : members)
+            {
+                text += (text.size() > 1 ? ",\"" : "\"") + m.key + "\":" + std::to_string(m.position);
+                last[m.key] = m.position;
+            }
+            text += '}';
+            REQUIRE(last.size() < members.size());
+
+            const json_document d = json_document::parse(text);
+            const json_view v = d.root();
+            const json j = json::parse(text);
+            CHECK(v.size() == members.size()); // every occurrence is visited
+            for (const auto& entry : last)
+            {
+                CAPTURE(entry.first)
+                const std::size_t expected = entry.second;
+                CHECK(v[entry.first].get<std::size_t>() == expected);
+                CHECK(v.at(entry.first).get<std::size_t>() == expected);
+                CHECK(v.find(entry.first).value().get<std::size_t>() == expected);
+                CHECK(v.value(entry.first, std::size_t{0}) == expected);
+                CHECK(v.contains(entry.first));
+                CHECK(v.count(entry.first) == 1);
+                const std::string pointer = "/" + entry.first;
+                CHECK(v[json::json_pointer(pointer)].get<std::size_t>() == expected);
+                CHECK(v.at(json::json_pointer(pointer)).get<std::size_t>() == expected);
+                CHECK(v.value(json::json_pointer(pointer), std::size_t{0}) == expected);
+                CHECK(v.contains(json::json_pointer(pointer)));
+                CHECK(j[entry.first].get<std::size_t>() == expected); // as materialize() and parse() keep it
+            }
+            CHECK(!v.contains("k"));
+            CHECK(v["missing"].is_discarded());
+            CHECK(v.materialize() == j);
+            CHECK(v == j);
+        }
+    }
+
+    SECTION("colliding keys")
+    {
+        // the hash is not seeded, so keys that all land in one place must not
+        // make the table build quadratic: such an object gets no table and is
+        // searched linearly
+        constexpr std::size_t members = 300;
+        constexpr std::size_t slots = 1024; // the table size for 300 members: the next power of two >= 600
+        std::vector<std::string> colliding;
+        std::vector<std::string> spread;
+        for (std::uint64_t counter = 0; colliding.size() < members || spread.size() < members; ++counter)
+        {
+            std::string key(8, 'a');
+            for (std::uint64_t x = counter, i = 0; i < 8; ++i, x /= 26)
+            {
+                key[i] = static_cast<char>('a' + (x % 26));
+            }
+            const bool lands_in_slot_zero = (nlohmann::detail::view::key_hash(key.data(), key.size()) & (slots - 1)) == 0;
+            if (lands_in_slot_zero && colliding.size() < members)
+            {
+                colliding.push_back(key);
+            }
+            else if (!lands_in_slot_zero && spread.size() < members)
+            {
+                spread.push_back(key);
+            }
+        }
+
+        const auto make_text = [](const std::vector<std::string>& keys)
+        {
+            std::string text = "{";
+            for (std::size_t i = 0; i < keys.size(); ++i)
+            {
+                text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i % 10);
+            }
+            return text + "}";
+        };
+        const std::string colliding_text = make_text(colliding);
+        const std::string spread_text = make_text(spread);
+
+        json_document with_collisions = json_document::parse(colliding_text);
+        json_document without_collisions = json_document::parse(spread_text);
+        for (const auto* pair :
+                {
+                    &colliding, &spread
+                })
+        {
+            const json_view v = (pair == &colliding ? with_collisions : without_collisions).root();
+            for (std::size_t i = 0; i < members; ++i)
+            {
+                CAPTURE(i)
+                CHECK(v[(*pair)[i]].get<std::size_t>() == i % 10);
+                CHECK(v.at((*pair)[i]).get<std::size_t>() == i % 10);
+                CHECK(v.find((*pair)[i]).key() == (*pair)[i]);
+                CHECK(!v.contains((*pair)[i] + "x"));
+            }
+            CHECK(!v.contains("missing"));
+        }
+        CHECK(with_collisions.root() == json::parse(colliding_text));
+
+        // only the object with the spread keys got a table (both texts have the
+        // same length, so the tables are the only difference)
+        with_collisions.shrink_to_fit();
+        without_collisions.shrink_to_fit();
+        CHECK(without_collisions.memory_usage() >= with_collisions.memory_usage() + (slots * sizeof(std::uint32_t)));
+    }
+
+    SECTION("shrink_to_fit releases the tables' spare capacity")
+    {
+        const auto make_text = [](int objects, int members)
+        {
+            std::string text = "[";
+            for (int object = 0; object < objects; ++object)
+            {
+                text += object != 0 ? ",{" : "{";
+                for (int i = 0; i < members + object; ++i)
+                {
+                    text += (i != 0 ? ",\"" : "\"") + std::to_string(i) + "\":" + std::to_string(i);
+                }
+                text += '}';
+            }
+            return text + "]";
+        };
+        const std::string small_text = make_text(5, 150);
+        const std::string big_text = make_text(40, 400);
+
+        // reading a big text, and then a small one, leaves the spare capacity
+        // of the big one: shrink_to_fit() brings the document to the size of
+        // one parsed from the small text alone
+        json_document d = json_document::parse(big_text);
+        const std::size_t big = d.memory_usage();
+        d.read(small_text);
+        CHECK(d.memory_usage() >= big);
+        d.shrink_to_fit();
+        json_document fresh = json_document::parse(small_text);
+        fresh.shrink_to_fit();
+        CHECK(d.memory_usage() == fresh.memory_usage());
+        CHECK(d.memory_usage() < big / 2);
+        CHECK(d.root() == json::parse(small_text));
+        for (int object = 0; object < 5; ++object)
+        {
+            const json_view v = d.root()[static_cast<std::size_t>(object)];
+            for (int i = 0; i < 150 + object; ++i)
+            {
+                CHECK(v[std::to_string(i)].get<int>() == i);
+            }
+        }
+    }
+
     SECTION("nested, reused, and in arrays")
     {
         std::string inner = "{";

tests/src/unit-json_view_builder.cpp

@@ -20,8 +20,10 @@ using nlohmann::json;
 #include <array>
 #include <cstdint>
 #include <fstream>
+#include <limits>
 #include <map>
 #include <memory>
+#include <new>
 #include <random>
 #include <sstream>
 #include <string>
@@ -506,3 +508,89 @@ TEST_CASE("json_view builder: strings across vector blocks")
         }
     }
 }
+
+TEST_CASE("json_view node integer bits")
+{
+    using nlohmann::detail::view::integer_bits;
+    using nlohmann::detail::view::set_integer_bits;
+
+    // an integer lives in len (low half) and next (high half), on any byte
+    // order; a big-endian target must not store the native word over both
+    SECTION("set_integer_bits and integer_bits")
+    {
+        node n = {};
+        for (const std::uint64_t v :
+                {
+                    std::uint64_t{0}, std::uint64_t{1}, std::uint64_t{0xFFFFFFFFu}, std::uint64_t{0x100000000u},
+                    std::uint64_t{0x0000000200000003u}, std::uint64_t{0x0123456789ABCDEFu}, std::uint64_t{0xFFFFFFFFFFFFFFFEu}
+                })
+        {
+            CAPTURE(v)
+            n.kind = 0x5A;
+            n.flags = 0xA5;
+            n.extra = 0x1234;
+            n.off = 0x89ABCDEFu;
+            set_integer_bits(n, v);
+            CHECK(integer_bits(n) == v);
+            CHECK(n.len == static_cast<std::uint32_t>(v));
+            CHECK(n.next == static_cast<std::uint32_t>(v >> 32));
+            // the other fields are untouched
+            CHECK(n.kind == 0x5A);
+            CHECK(n.flags == 0xA5);
+            CHECK(n.extra == 0x1234);
+            CHECK(n.off == 0x89ABCDEFu);
+        }
+    }
+
+    SECTION("parsed integers")
+    {
+        struct integer_case
+        {
+            const char* text;
+            std::uint64_t bits;
+        };
+        for (const integer_case c :
+                {
+                    integer_case{"[8589934595]", 0x0000000200000003u}, integer_case{"[4294967296]", 0x100000000u}, integer_case{"[4294967295]", 0xFFFFFFFFu},
+                    integer_case{"[-2]", 0xFFFFFFFFFFFFFFFEu}, integer_case{"[-4294967297]", 0xFFFFFFFEFFFFFFFFu}, integer_case{"[18446744073709551615]", 0xFFFFFFFFFFFFFFFFu},
+                    integer_case{"[7]", 7u}
+                })
+        {
+            CAPTURE(c.text)
+            const built b = build(c.text, false, false, true);
+            REQUIRE(b.ok);
+            const node& n = b.data->tape[1];
+            CHECK(integer_bits(n) == c.bits);
+            CHECK(n.len == static_cast<std::uint32_t>(c.bits));
+            CHECK(n.next == static_cast<std::uint32_t>(c.bits >> 32));
+        }
+    }
+}
+
+TEST_CASE("json_view node array size limit")
+{
+    // a node array larger than the address space is refused, not wrapped to a
+    // small allocation (the size computation overflows on 32-bit targets, and
+    // for absurd counts everywhere)
+    std::unique_ptr<document_data, document_data::deleter> d(document_data::create(0));
+    d->reserve(8);
+    REQUIRE(d->tape_cap >= 8);
+    d->tape_size = 2;
+    const std::size_t cap = d->tape_cap;
+    node* const tape = d->tape;
+
+#if !defined(JSON_NOEXCEPTION)
+    const std::size_t too_many = document_data::max_nodes() + 1;
+    CHECK_THROWS_AS(d->reserve(too_many), std::bad_alloc&);
+    CHECK_THROWS_AS(d->reserve((std::numeric_limits<std::size_t>::max)()), std::bad_alloc&);
+    // the array is unchanged
+    CHECK(d->tape == tape);
+    CHECK(d->tape_cap == cap);
+    CHECK(d->tape_size == 2);
+#endif
+
+    // the largest count that fits is not refused by the check (nothing is
+    // allocated for a count that is already there)
+    d->reserve(cap);
+    CHECK(d->tape == tape);
+}

tests/src/unit-json_view_edit.cpp

@@ -181,6 +181,104 @@ void compare(const ordered_json_editable_view& v, const ordered_json& j)
     }
 }
 
+// the text of j, in which some objects repeat a key of theirs: before their
+// members (the real member is then the last), or after (the repeat is)
+std::string text_with_duplicates(const ordered_json& j)
+{
+    if (j.is_object())
+    {
+        std::vector<std::string> keys;
+        for (const auto& kv : j.items())
+        {
+            keys.push_back(kv.key());
+        }
+        const auto repeated = [&keys]()
+        {
+            return ordered_json(keys[static_cast<std::size_t>(r(static_cast<int>(keys.size())))]).dump() + ":" + random_value(2).dump();
+        };
+        std::string text = "{";
+        if (!keys.empty() && r(4) == 0)
+        {
+            text += repeated() + ",";
+        }
+        bool first = true;
+        for (const auto& kv : j.items())
+        {
+            text += (first ? "" : ",") + ordered_json(kv.key()).dump() + ":" + text_with_duplicates(kv.value());
+            first = false;
+        }
+        for (int i = keys.empty() ? 0 : r(3); i > 0; --i)
+        {
+            text += "," + repeated();
+        }
+        return text + "}";
+    }
+    if (j.is_array())
+    {
+        std::string text = "[";
+        for (std::size_t i = 0; i < j.size(); ++i)
+        {
+            text += (i != 0 ? "," : "") + text_with_duplicates(j[i]);
+        }
+        return text + "]";
+    }
+    return j.dump();
+}
+
+// every lookup of the edited view finds what j holds, although the view may
+// have several members for a key (j has the last value, at the position of the
+// first member: what parse() and materialize() make of it)
+void check_lookups(const ordered_json_editable_view& v, const ordered_json& j)
+{
+    REQUIRE(v.type() == j.type());
+    if (j.is_object())
+    {
+        for (const auto& kv : j.items())
+        {
+            const std::string& key = kv.key();
+            const ptr_t ptr = ptr_t() / key;
+            CAPTURE(key)
+            const ordered_json_editable_view m = v[key];
+            REQUIRE(!m.is_discarded());
+            CHECK(m.materialize() == kv.value());
+            CHECK(v.at(key).materialize() == kv.value());
+            CHECK(v[ptr].materialize() == kv.value());
+            CHECK(v.at(ptr).materialize() == kv.value());
+            CHECK(v.contains(key));
+            CHECK(v.contains(ptr));
+            CHECK(v.count(key) == 1);
+            const auto it = v.find(key);
+            REQUIRE(it != v.end());
+            CHECK((*it).materialize() == kv.value());
+            CHECK(v.value(ptr, ordered_json(nullptr)) == kv.value());
+            if (kv.value().is_string())
+            {
+                CHECK(v.value(key, std::string("-")) == kv.value().get<std::string>());
+            }
+            check_lookups(m, kv.value());
+        }
+        CHECK(v["missing#key"].is_discarded());
+        CHECK(!v.contains("missing#key"));
+        CHECK(v.find("missing#key") == v.end());
+    }
+    else if (j.is_array())
+    {
+        for (std::size_t i = 0; i < j.size(); ++i)
+        {
+            check_lookups(v[i], j[i]);
+            check_lookups(v.at(i), j[i]);
+        }
+    }
+}
+
+// (for documents whose objects repeat keys: dump(), size(), and iteration
+// list all members, so only the lookups and materialize() are compared)
+void check_duplicates(const ordered_json_editable_document& d, const ordered_json& j)
+{
+    CHECK(d.root().materialize() == j);
+    check_lookups(d.root(), j);
+}
+
 void check_all(const ordered_json_editable_document& d, const ordered_json& j, bool deep)
 {
     const std::string text = d.root().dump();
@@ -204,14 +302,16 @@ TEST_CASE("json_view edits: differential")
     // random edits are applied to an ordered_json_editable_document and to the
     // ordered_json parse() produces; after every edit both must serialize,
     // materialize, and read back the same
-    for (int n = 0; n < 150; ++n)
+    for (int n = 0; n < 250; ++n)
     {
+        // the last 100 documents repeat keys in some of their objects
+        const bool duplicates = n >= 150;
         ordered_json j = random_value(0);
         if (r(4) == 0)
         {
             j = ordered_json::object({{"a", random_value(1)}, {"b", random_value(1)}});
         }
-        const std::string text = j.dump(r(2) == 0 ? -1 : 2);
+        const std::string text = duplicates ? text_with_duplicates(j) : j.dump(r(2) == 0 ? -1 : 2);
         CAPTURE(text)
         ordered_json_editable_document d = ordered_json_editable_document::parse(text);
         j = ordered_json::parse(text);
@@ -340,7 +440,14 @@ TEST_CASE("json_view edits: differential")
             }
             CAPTURE(p.to_string())
             CAPTURE(op)
-            check_all(d, j, e % 8 == 7 || e == edits - 1);
+            if (duplicates)
+            {
+                check_duplicates(d, j);
+            }
+            else
+            {
+                check_all(d, j, e % 8 == 7 || e == edits - 1);
+            }
         }
     }
 }
@@ -517,7 +624,7 @@ TEST_CASE("json_view edits: views and values")
     SECTION("duplicate keys")
     {
         json_editable_document d = json_editable_document::parse(R"({"a": 1, "b": 2, "a": 3})");
-        d.set(d.root(), "a", 4); // the first member is assigned, the others dropped
+        d.set(d.root(), "a", 4); // the last member is assigned (at the position of the first), the others dropped
         CHECK(d.root().dump() == R"({"a":4,"b":2})");
         d = json_editable_document::parse(R"({"a": 1, "b": 2, "a": 3})");
         CHECK(d.erase(d.root(), "a") == 2);
@@ -577,3 +684,393 @@ TEST_CASE("json_view edits: views and values")
         CHECK(d.root().dump() == "[true,false]");
     }
 }
+
+TEST_CASE("json_view edits: deeply nested values")
+{
+    // copying a value into a document must not recurse per nesting level
+    const std::size_t depth = 100000;
+    const std::string brackets = std::string(depth, '[') + std::string(depth, ']');
+    std::string braces;
+    for (std::size_t i = 0; i < depth; ++i)
+    {
+        braces += "{\"a\":";
+    }
+    braces += '1';
+    braces += std::string(depth, '}');
+
+    SECTION("a view of a read-only document")
+    {
+        const json_document source = json_document::parse(brackets);
+        json_editable_document d = json_editable_document::parse("[]");
+        d.push_back(d.root(), source.root());
+        CHECK(d.root().dump() == "[" + brackets + "]");
+    }
+
+    SECTION("a view of an editable document")
+    {
+        const json_editable_document source = json_editable_document::parse(braces);
+        json_editable_document d = json_editable_document::parse("{}");
+        d.set(d.root(), "deep", source.root());
+        CHECK(d.root().dump() == "{\"deep\":" + braces + "}");
+    }
+
+    SECTION("a view of an edited document (values behind links)")
+    {
+        const json_document source = json_document::parse(brackets);
+        json_editable_document edited = json_editable_document::parse("[[]]");
+        edited.push_back(edited.root()[0], source.root());
+        edited.push_back(edited.root(), source.root());
+        json_editable_document d = json_editable_document::parse("null");
+        d.set(d.root(), edited.root());
+        CHECK(d.root().dump() == "[[" + brackets + "]," + brackets + "]");
+    }
+
+    SECTION("a basic_json value")
+    {
+        json deep = json::array();
+        json* inner = &deep;
+        for (std::size_t i = 1; i < depth; ++i)
+        {
+            inner->push_back(json::array());
+            inner = &inner->back();
+        }
+        json_editable_document d = json_editable_document::parse("[]");
+        d.push_back(d.root(), deep);
+        CHECK(d.root().dump() == "[" + brackets + "]");
+    }
+
+    SECTION("a basic_json value with objects")
+    {
+        json deep = 1;
+        for (std::size_t i = 0; i < depth; ++i)
+        {
+            json outer = json::object();
+            outer["a"] = std::move(deep);
+            deep = std::move(outer);
+        }
+        json_editable_document d = json_editable_document::parse("{}");
+        d.set(d.root(), "deep", deep);
+        CHECK(d.root().dump() == "{\"deep\":" + braces + "}");
+    }
+}
+
+#if !defined(JSON_NOEXCEPTION)
+TEST_CASE("json_view edits: pointers below a null value")
+{
+    // a null value on the way becomes what basic_json makes of it: an array
+    // for "-" and for digits, an object otherwise
+    struct test_case
+    {
+        const char* document;
+        const char* pointer;
+    };
+    const std::array<test_case, 16> cases =
+    {
+        {
+            {R"({"a":null})", "/a/0"},
+            {R"({"a":null})", "/a/-"},
+            {R"({"a":null})", "/a/3"},
+            {R"({"a":null})", "/a/x"},
+            {R"({"a":null})", "/a/+1"},
+            {R"({"a":null})", "/a/01"},
+            {R"({"a":null})", "/a/"},
+            {R"({"a":{"b":null}})", "/a/b/1"},
+            {R"({"a":{"b":null}})", "/a/b/-"},
+            {R"({"a":[null]})", "/a/0/0"},
+            {R"({"a":[null,null]})", "/a/1/k"},
+            {R"([null])", "/0"},
+            {"null", "/0"},
+            {"null", "/-"},
+            {"null", "/k"},
+            {"null", ""},
+        }
+    };
+    for (const test_case& c : cases)
+    {
+        CAPTURE(c.document)
+        CAPTURE(c.pointer)
+        json expected = json::parse(c.document);
+        const std::string error = exception_of_call([&]
+        {
+            expected[json::json_pointer(c.pointer)] = 1;
+        });
+        json_editable_document d = json_editable_document::parse(c.document);
+        if (error.empty())
+        {
+            d.set(json::json_pointer(c.pointer), 1);
+            CHECK(d.root().dump() == expected.dump());
+            CHECK(d.root().materialize() == expected);
+        }
+        else
+        {
+            // the same error, and the document is not changed
+            CHECK(exception_of_call([&] { d.set(json::json_pointer(c.pointer), 1); }) == error);
+            CHECK(d.root().dump() == json::parse(c.document).dump());
+        }
+    }
+}
+
+TEST_CASE("json_view edits: strings of other documents are checked")
+{
+    // A document borrows the text it was parsed from, and sees later changes
+    // of the text: a way to get ill-formed UTF-8 into a view. Copying it into
+    // an editable document is an error, as for any other string.
+    std::string text = R"({"key":"abc","list":["abc"]})";
+    const json_document source = json_document::parse(text);
+    const auto message_of = [](const std::string & bad)
+    {
+        return exception_of_call([&]
+        {
+            const std::string dumped = json(bad).dump();
+            static_cast<void>(dumped);
+        });
+    };
+    json_editable_document d = json_editable_document::parse("[1]");
+    d.push_back(d.root(), source.root());
+    CHECK(d.root().dump() == R"([1,{"key":"abc","list":["abc"]}])");
+
+    text[text.find("abc") + 1] = '\xC3'; // "a\xC3c"
+    text[text.rfind("abc") + 1] = '\xC3';
+    const std::string bad_value = message_of(std::string("a\xC3" "c"));
+    CHECK(!bad_value.empty());
+    CHECK(exception_of_call([&] { d.push_back(d.root(), source.root()["key"]); }) == bad_value);
+    CHECK(exception_of_call([&] { d.set(d.root()[0], source.root()["list"][0]); }) == bad_value);
+    CHECK(exception_of_call([&] { d.set(d.root(), 0, source.root()["list"]); }) == bad_value);
+    CHECK(exception_of_call([&] { d.set(d.root(), 0, source.root()); }) == bad_value);
+
+    text[text.find("key") + 1] = '\xC3'; // a key is checked as well
+    const std::string bad_key = message_of(std::string("k\xC3" "y"));
+    CHECK(exception_of_call([&] { d.set(d.root(), 0, source.root()); }) == bad_key);
+    CHECK(exception_of_call([&] { d.push_back(d.root(), source.root()); }) == bad_key);
+
+    // nothing of the failed edits is visible
+    CHECK(d.root().dump() == R"([1,{"key":"abc","list":["abc"]}])");
+}
+
+TEST_CASE("json_view edits: the size of a text arena")
+{
+    using nlohmann::detail::view::text_capacity;
+    constexpr std::size_t limit = 0xFFFFFFFFu;
+    // grows by doubling, or to what is needed (plus some room)
+    CHECK(text_capacity(0, 0, 10) == 266);
+    CHECK(text_capacity(1000, 990, 20) == 2000);
+    CHECK(text_capacity(100, 100, 5000) == 5356);
+    // an arena beyond 2 GiB: doubling is clamped to 4 GiB - 1
+    CHECK(text_capacity(0x90000000u, 0x8FFFFFFFu, 2) == limit);
+    CHECK(text_capacity(limit, limit - 10, 10) == limit);
+    // exactly what fits is accepted, without room to spare
+    CHECK(text_capacity(100, 90, limit - 90) == limit);
+    CHECK(text_capacity(limit - 100, limit - 100, 100) == limit);
+    // what does not fit is an error
+    CHECK_THROWS_WITH_AS(text_capacity(100, 90, limit - 89), "[json.exception.out_of_range.416] edits of 4 GiB or more are not supported by json_document", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(text_capacity(limit, limit, 1), "[json.exception.out_of_range.416] edits of 4 GiB or more are not supported by json_document", json::out_of_range&);
+}
+#endif
+
+TEST_CASE("json_view edits: replacing arrays and objects by scalars")
+{
+    // the first assignment switches the parent to links; the later ones do
+    // not need to look for the parent again
+    std::string text = "[";
+    json expected = json::array();
+    for (int i = 0; i < 300; ++i)
+    {
+        text += (i != 0 ? ",[" : "[") + std::to_string(i) + ",{\"k\":" + std::to_string(i) + "}]";
+        expected.push_back(json::array({i, json{{"k", i}}}));
+    }
+    text += ']';
+    json_editable_document d = json_editable_document::parse(text);
+    CHECK(d.root().dump() == expected.dump());
+    for (int i = 0; i < 300; i += 2)
+    {
+        d.set(d.root()[static_cast<std::size_t>(i)], i);
+        expected[static_cast<std::size_t>(i)] = i;
+    }
+    CHECK(d.root().dump() == expected.dump());
+    for (int i = 1; i < 300; i += 2) // (elements that are still in the parsed layout of their parent)
+    {
+        d.set(d.root()[static_cast<std::size_t>(i)][1], "x"); // replaces an object
+        expected[static_cast<std::size_t>(i)][1] = "x";
+    }
+    CHECK(d.root().dump() == expected.dump());
+
+    // new values, and values in new values
+    d.push_back(d.root(), json::parse(R"([[1,2],{"a":[3]}])"));
+    expected.push_back(json::parse(R"([[1,2],{"a":[3]}])"));
+    d.set(d.root()[300][0], 7);
+    expected[300][0] = 7;
+    d.insert(d.root(), 0, json::array({1, 2}));
+    expected.insert(expected.begin(), json::array({1, 2}));
+    d.set(d.root()[0], nullptr);
+    expected[0] = nullptr;
+    d.set(d.root()[301], 5);
+    expected[301] = 5;
+    CHECK(d.root().dump() == expected.dump());
+    CHECK(d.root().materialize() == expected);
+}
+
+namespace
+{
+// reads of "a" in an object that repeats it: the last member wins, however the
+// object is stored
+template<typename View>
+void check_last_wins(const View& o, int expected)
+{
+    CAPTURE(expected)
+    CHECK(o["a"].template get<int>() == expected);
+    CHECK(o.at("a").template get<int>() == expected);
+    CHECK(o.find("a")->template get<int>() == expected);
+    CHECK(o.value("a", -1) == expected);
+    CHECK(o[json::json_pointer("/a")].template get<int>() == expected);
+    CHECK(o.at(json::json_pointer("/a")).template get<int>() == expected);
+    CHECK(o.value(json::json_pointer("/a"), -1) == expected);
+    CHECK(o.contains("a"));
+    CHECK(o.contains(json::json_pointer("/a")));
+    CHECK(o.count("a") == 1);
+}
+} // namespace
+
+TEST_CASE("json_view edits: duplicate keys")
+{
+    SECTION("an object in its parsed layout, then moved by edits")
+    {
+        json_editable_document d = json_editable_document::parse(R"({"a": 1, "b": 2, "a": 3})");
+        check_last_wins(d.root(), 3);
+        CHECK(d.root().size() == 3);
+        CHECK(d.root().dump() == R"({"a":1,"b":2,"a":3})");
+
+        // an edit of a value does not move the object
+        d.set(d.root()["b"], 5);
+        check_last_wins(d.root(), 3);
+        d.set(d.root()["a"], 4); // the member that reads find
+        check_last_wins(d.root(), 4);
+        CHECK(d.root().dump() == R"({"a":1,"b":5,"a":4})");
+
+        // an appended member moves it
+        d.set(d.root(), "c", true);
+        check_last_wins(d.root(), 4);
+        CHECK(d.root().size() == 4);
+        CHECK(d.root().dump() == R"({"a":1,"b":5,"a":4,"c":true})");
+        d.set(d.root()["a"], 6);
+        check_last_wins(d.root(), 6);
+        CHECK(d.root().dump() == R"({"a":1,"b":5,"a":6,"c":true})");
+        d.set(json::json_pointer("/a"), 7);
+        check_last_wins(d.root(), 7);
+    }
+
+    SECTION("set assigns the member that reads find")
+    {
+        // the key keeps the position of its first occurrence (as in materialize()), the later members are dropped
+        ordered_json_editable_document d = ordered_json_editable_document::parse(R"({"a": 1, "b": 2, "a": 3, "c": 4, "a": 5})");
+        const ordered_json_editable_view held = d.root()["a"];
+        CHECK(held.get<int>() == 5);
+        const ordered_json_editable_view assigned = d.set(d.root(), "a", "x");
+        CHECK(held.get<std::string>() == "x");
+        CHECK(assigned.get<std::string>() == "x");
+        CHECK(d.root().dump() == R"({"a":"x","b":2,"c":4})");
+        CHECK(d.root().materialize() == ordered_json::parse(R"({"a": "x", "b": 2, "c": 4})"));
+        CHECK(d.root().size() == 3);
+
+        // as for the object that parse() makes of the text
+        ordered_json j = ordered_json::parse(R"({"a": 1, "b": 2, "a": 3, "c": 4, "a": 5})");
+        j["a"] = "x";
+        CHECK(d.root().materialize().dump() == j.dump());
+
+        // through a pointer, below a duplicate
+        d = ordered_json_editable_document::parse(R"({"a": {"x": 1}, "b": 2, "a": {"x": 3}})");
+        d.set(ptr_t("/a/x"), 4);
+        CHECK(d.root().dump() == R"({"a":{"x":1},"b":2,"a":{"x":4}})");
+        d.set(ptr_t("/a"), 0);
+        CHECK(d.root().dump() == R"({"a":0,"b":2})");
+    }
+
+    SECTION("erase removes every member")
+    {
+        json_editable_document d = json_editable_document::parse(R"({"a": 1, "b": 2, "a": 3})");
+        d.set(d.root(), "c", 4);
+        check_last_wins(d.root(), 3);
+        CHECK(d.erase(d.root(), "a") == 2);
+        CHECK(d.root().dump() == R"({"b":2,"c":4})");
+        CHECK(!d.root().contains("a"));
+        CHECK(d.root()["a"].is_discarded());
+        CHECK(d.erase(d.root(), "a") == 0);
+        d = json_editable_document::parse(R"({"a": 1, "b": 2, "a": 3})");
+        CHECK(d.erase(json::json_pointer("/a")) == 2);
+        CHECK(d.root().dump() == R"({"b":2})");
+    }
+
+    SECTION("a large object with an index")
+    {
+        std::string text = R"({"a":0,"k7":"first")";
+        for (int i = 0; i < 200; ++i)
+        {
+            text += ",\"k" + std::to_string(i) + "\":" + std::to_string(i);
+        }
+        text += R"(,"a":1,"k7":"last","a":2})";
+        json_editable_document d = json_editable_document::parse(text);
+        check_last_wins(d.root(), 2);
+        CHECK(d.root()["k7"].get_string() == "last");
+        CHECK(d.root()["k199"].get<int>() == 199);
+
+        // a value assigned in place: the index stays in use
+        d.set(d.root()["a"], 3);
+        check_last_wins(d.root(), 3);
+        d.set(d.root()["k7"], "changed");
+        CHECK(d.root()["k7"].get_string() == "changed");
+        CHECK(d.root()["k199"].get<int>() == 199);
+
+        // an appended member moves the members: the lookup scans them
+        d.set(d.root(), "new", 1);
+        check_last_wins(d.root(), 3);
+        CHECK(d.root()["k7"].get_string() == "changed");
+        CHECK(d.root()["k7"].get_string() == d.root().at("k7").get_string());
+        CHECK(d.root()["k199"].get<int>() == 199);
+        CHECK(d.root()["new"].get<int>() == 1);
+
+        // a value replaced by a container, in an object that was not moved
+        d = json_editable_document::parse(text);
+        d.set(d.root()["a"], json{{"x", 1}});
+        CHECK(d.root()["a"]["x"].get<int>() == 1);
+        CHECK(d.root()["k7"].get_string() == "last");
+        CHECK(d.erase(d.root(), "k7") == 3); // (the key occurs three times)
+        CHECK(d.root()["k7"].is_discarded());
+        CHECK(d.root()["a"]["x"].get<int>() == 1);
+    }
+
+    SECTION("objects in moved arrays and in new values")
+    {
+        json_editable_document d = json_editable_document::parse(R"([{"a": 1, "a": 2}, {"a": 3, "b": 0, "a": 4}])");
+        check_last_wins(d.root()[0], 2);
+        check_last_wins(d.root()[1], 4);
+        d.insert(d.root(), 0, json::parse(R"({"a": 0})"));
+        d.push_back(d.root(), json::parse(R"({"a": 5, "a": 6})")); // (a basic_json value has one member)
+        check_last_wins(d.root()[1], 2);
+        check_last_wins(d.root()[2], 4);
+        CHECK(d.root()[3]["a"].get<int>() == 6);
+        d.set(d.root()[1], "a", 8);
+        check_last_wins(d.root()[1], 8);
+        CHECK(d.root()[1].dump() == R"({"a":8})");
+        d.erase(d.root(), 0);
+        check_last_wins(d.root()[1], 4);
+        CHECK(d.root().dump() == R"([{"a":8},{"a":3,"b":0,"a":4},{"a":6}])");
+    }
+
+    SECTION("values of other documents")
+    {
+        const json_document source = json_document::parse(R"({"list": [{"a": 1, "a": 2}], "o": {"b": {"a": 3, "a": 4}, "a": 5, "a": 6}})");
+        json_editable_document d = json_editable_document::parse("{}");
+        d.set(d.root(), "copy", source.root()["list"]);
+        d.set(d.root(), "o", source.root()["o"]);
+        // (the copies keep the repeated members)
+        CHECK(d.root().dump() == R"({"copy":[{"a":1,"a":2}],"o":{"b":{"a":3,"a":4},"a":5,"a":6}})");
+        check_last_wins(d.root()["copy"][0], 2);
+        check_last_wins(d.root()["o"]["b"], 4);
+        check_last_wins(d.root()["o"], 6);
+        d.set(d.root()["o"]["b"], "c", 0);
+        check_last_wins(d.root()["o"]["b"], 4);
+        d.set(d.root()["o"], "d", 0);
+        check_last_wins(d.root()["o"], 6);
+        CHECK(d.root()["o"]["b"]["a"].get<int>() == 4);
+        CHECK(d.root()["o"]["d"].get<int>() == 0);
+    }
+}

tests/src/unit-json_view_image.cpp

@@ -18,6 +18,7 @@ using nlohmann::ordered_json_editable_document;
 using image_check = json_document::image_check;
 using nlohmann::detail::view::node;
 
+#include <algorithm>
 #include <array>
 #include <cstdint>
 #include <cstring>
@@ -61,6 +62,14 @@ std::string read_file(const std::string& name)
     return ss.str();
 }
 
+// the dump of a loaded image, through a named document (root() of a temporary
+// document does not compile, and its views would dangle)
+std::string loaded_dump(const std::vector<std::uint8_t>& image, image_check check = image_check::full)
+{
+    const json_document d = json_document::load(image, check);
+    return d.root().dump();
+}
+
 // the offsets of the parts of an image
 constexpr std::size_t header_size = 64;
 
@@ -191,7 +200,8 @@ TEST_CASE("json_view images: round trips")
             const json_document d = json_document::parse(text);
             check_round_trip(d);
             // what a loaded document reads is what parse() produces
-            CHECK(json_document::load(d.save()).root().materialize() == json::parse(text));
+            const json_document l = json_document::load(d.save());
+            CHECK(l.root().materialize() == json::parse(text));
         }
     }
 
@@ -231,7 +241,7 @@ TEST_CASE("json_view images: round trips")
             {
                 CHECK(l.root()["k" + std::to_string(i)] == d.root()["k" + std::to_string(i)]);
             }
-            CHECK(l.root()["k7"].get<int>() == 7); // the first of duplicate keys
+            CHECK(l.root()["k7"] == "a duplicate"); // the last of duplicate keys
             CHECK(l.root()["inner"]["m199"].get<int>() == -199);
             CHECK(!l.root().contains("k1000"));
             // the index is not part of the image
@@ -240,6 +250,155 @@ TEST_CASE("json_view images: round trips")
         // the nodes of objects in the image do not carry the number of an index
         CHECK(node_at(image, 0).extra == 0);
     }
+
+    SECTION("duplicate keys of a large object: lookups return the last member")
+    {
+        std::string text = "{";
+        for (int i = 0; i < 200; ++i)
+        {
+            text += (i != 0 ? ",\"k" : "\"k") + std::to_string(i) + "\":" + std::to_string(i);
+        }
+        // three members for k5 (the third is the last), and duplicates of k0 and k199
+        text += R"(,"k5":"two","k0":null,"k199":[],"k5":"three"})";
+        const json_document d = json_document::parse(text);
+        REQUIRE(d.root().size() == 204);
+        CHECK(d.root()["k5"] == "three");
+        const std::vector<std::uint8_t> image = d.save();
+        for (const image_check check :
+                {
+                    image_check::full, image_check::bounds, image_check::none
+                })
+        {
+            const json_document l = json_document::load(image, check);
+            CHECK(l.root().size() == 204);
+            CHECK(l.root()["k5"] == "three");
+            CHECK(l.root().at("k5") == "three");
+            CHECK(l.root().find("k5").value() == "three");
+            CHECK(l.root()["k0"].is_null());
+            CHECK(l.root()["k199"] == json::array());
+            CHECK(l.root()["k100"] == 100);
+            CHECK(l.root().materialize() == d.root().materialize());
+        }
+    }
+
+    SECTION("objects with colliding keys")
+    {
+        // the hash is not seeded: keys can be found that land in one slot of
+        // a table (see json_view: "colliding keys")
+        const auto keys_for = [](std::size_t slots, std::size_t colliding_count, std::size_t spread_count)
+        {
+            std::vector<std::string> colliding;
+            std::vector<std::string> spread;
+            for (std::uint64_t counter = 0; colliding.size() < colliding_count || spread.size() < spread_count; ++counter)
+            {
+                std::string key(8, 'a');
+                for (std::uint64_t x = counter, i = 0; i < 8; ++i, x /= 26)
+                {
+                    key[i] = static_cast<char>('a' + (x % 26));
+                }
+                const bool lands_in_slot_zero = (nlohmann::detail::view::key_hash(key.data(), key.size()) & (slots - 1)) == 0;
+                if (lands_in_slot_zero && colliding.size() < colliding_count)
+                {
+                    colliding.push_back(key);
+                }
+                else if (!lands_in_slot_zero && spread.size() < spread_count)
+                {
+                    spread.push_back(key);
+                }
+            }
+            colliding.insert(colliding.end(), spread.begin(), spread.end());
+            return colliding;
+        };
+        const auto make_text = [](const std::vector<std::string>& keys)
+        {
+            std::string text = "{";
+            for (std::size_t i = 0; i < keys.size(); ++i)
+            {
+                text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i);
+            }
+            return text + "}";
+        };
+
+        // 300 keys in one slot (the table is 1024 slots): the table would
+        // exceed the probe limit, so the object has none and is searched
+        // linearly; 40 of 200 keys in one slot (512 slots): a table with a
+        // long chain
+        const struct
+        {
+            std::size_t slots;
+            std::size_t colliding;
+            std::size_t spread;
+        } cases[] = {{1024, 300, 0}, {512, 40, 160}};
+        for (const auto& c : cases)
+        {
+            CAPTURE(c.slots)
+            std::vector<std::string> keys = keys_for(c.slots, c.colliding, c.spread);
+            const std::size_t members = keys.size();
+            // a duplicate of a colliding key, of the first and of a spread key
+            const std::vector<std::string> duplicated = {keys[c.colliding - 1], keys[0], keys[members - 1]};
+            std::string text = make_text(keys);
+            text.pop_back();
+            for (const std::string& key : duplicated)
+            {
+                text += ",\"" + key + "\":\"last\"";
+            }
+            text += "}";
+            const json_document d = json_document::parse(text);
+            const std::vector<std::uint8_t> image = d.save();
+            for (const image_check check :
+                    {
+                        image_check::full, image_check::bounds, image_check::none
+                    })
+            {
+                const json_document l = json_document::load(image, check);
+                REQUIRE(l.root().size() == members + duplicated.size());
+                for (std::size_t i = 0; i < members; ++i)
+                {
+                    CAPTURE(i)
+                    const bool duplicate = std::find(duplicated.begin(), duplicated.end(), keys[i]) != duplicated.end();
+                    if (duplicate)
+                    {
+                        CHECK(l.root()[keys[i]] == "last");
+                    }
+                    else
+                    {
+                        CHECK(l.root()[keys[i]] == i);
+                    }
+                    CHECK(l.root().at(keys[i]) == l.root()[keys[i]]);
+                    CHECK(l.root().find(keys[i]).key() == keys[i]);
+                    CHECK(!l.root().contains(keys[i] + "x"));
+                }
+                CHECK(!l.root().contains("missing"));
+                CHECK(l.root().materialize() == json::parse(text));
+            }
+        }
+    }
+
+    SECTION("loading releases the list of large objects")
+    {
+        std::string text = "[";
+        for (int object = 0; object < 400; ++object)
+        {
+            text += object != 0 ? ",{" : "{";
+            for (int i = 0; i < 128; ++i)
+            {
+                text += (i != 0 ? ",\"" : "\"") + std::to_string(i) + "\":" + std::to_string(i);
+            }
+            text += '}';
+        }
+        text += "]";
+        json_document parsed = json_document::parse(text);
+        const std::vector<std::uint8_t> image = parsed.save();
+        json_document loaded = json_document::load(image);
+        CHECK(loaded.root()[399]["127"] == 127);
+        // Parsing and loading build the same tables, and keep nothing else:
+        // not the positions of the objects to index (2 KiB here). The slack
+        // covers the nodes in the header of the document, which are sized
+        // differently.
+        parsed.shrink_to_fit();
+        loaded.shrink_to_fit();
+        CHECK(loaded.memory_usage() <= parsed.memory_usage() + 512);
+    }
 }
 
 TEST_CASE("json_view images: edited documents")
@@ -305,6 +464,153 @@ TEST_CASE("json_view images: edited documents")
         CHECK(l.root()["list"].size() == 4);
     }
 
+    SECTION("the targets of links do not reach the image")
+    {
+        // Edits that make an entry of a moved sequence link to a value mark the
+        // value as linked (node_flags::linked). An image has no links and no
+        // such flag: the full and the bounds check reject it.
+        const std::string nested = R"({"a": [1, 2, {"x": [3]}, "s", 1.5, true, null, [4, 5]], "b": {"c": 1, "d": [1, 2, 3], "e": {"f": "g"}}, "h": "str"})";
+        const auto check_image = [](const json_editable_document & d)
+        {
+            const std::vector<std::uint8_t> image = d.save();
+            for (std::size_t i = 0; i < node_count(image); ++i)
+            {
+                CAPTURE(i)
+                CHECK((node_at(image, i).flags & nlohmann::detail::view::node_flags::linked) == 0);
+                CHECK(node_at(image, i).kind != nlohmann::detail::view::kind_link);
+            }
+            for (const image_check check :
+                    {
+                        image_check::full, image_check::bounds
+                    })
+            {
+                CHECK(load_result(image, check).empty());
+            }
+            check_round_trip(d);
+            // a loaded document is edited and saved again
+            json_editable_document e = json_editable_document::load(image);
+            CHECK(e.root().dump() == d.root().dump());
+            e.set(e.root(), "after", 1);
+            CHECK(loaded_dump(e.save()) == e.root().dump());
+        };
+
+        SECTION("a container replaced by a scalar after an earlier edit")
+        {
+            json_editable_document d = json_editable_document::parse(nested);
+            d.set(d.root()["a"][0], 9);
+            d.set(d.root()["a"][2], 5);
+            check_image(d);
+            d.set(d.root()["a"][2], "now a string");
+            check_image(d);
+            d.set(d.root()["a"][7], 0.25);
+            check_image(d);
+            d.set(d.root()["b"]["e"], true);
+            d.set(d.root()["b"]["d"], 7);
+            check_image(d);
+        }
+
+        SECTION("insert and push_back into parsed arrays")
+        {
+            json_editable_document d = json_editable_document::parse(nested);
+            d.push_back(d.root()["a"], 6);
+            check_image(d);
+            d.insert(d.root()["a"], 0, "first");
+            check_image(d);
+            d.insert(d.root()["b"]["d"], 1, json::array({1, 2}));
+            d.push_back(d.root()["b"]["d"], json::object({{"k", nullptr}}));
+            check_image(d);
+            // links to values that are replaced afterwards
+            d.set(d.root()["a"][3], json::object());
+            d.set(d.root()["a"][4], false);
+            d.set(d.root()["a"][5], "replaced");
+            d.set(d.root()["a"][9], 1e300);
+            check_image(d);
+        }
+
+        SECTION("members set in parsed objects")
+        {
+            json_editable_document d = json_editable_document::parse(nested);
+            d.set(d.root(), "new", 1);
+            d.set(d.root()["b"], "c", "changed");
+            d.set(d.root()["b"], "e", json::array({1, {{"z", 2}}}));
+            d.set(d.root()["b"], "more", d.root()["a"]);
+            check_image(d);
+            d.set(d.root()["a"][2], 3); // a link target in a copied subtree
+            d.erase(d.root()["b"], "c");
+            d.set(d.root(), "h", json::object());
+            check_image(d);
+        }
+
+        SECTION("erase")
+        {
+            json_editable_document d = json_editable_document::parse(nested);
+            d.push_back(d.root()["a"], 6);
+            d.erase(d.root()["a"], 0);
+            d.erase(d.root()["a"], 1);
+            d.set(d.root()["a"][0], 1);
+            d.erase(d.root()["b"], "d");
+            check_image(d);
+        }
+    }
+
+#if !defined(JSON_NOEXCEPTION)
+    SECTION("invalid UTF-8 of a loaded image is not copied into an editable document")
+    {
+        // loading with the bounds check (or none) does not look at the encoding
+        // of strings: dump() of such a view throws, and an editable document
+        // must not take the string over
+        const auto patched = [](const std::string & json_text)
+        {
+            std::vector<std::uint8_t> image = json_document::parse(json_text).save();
+            bool found = false;
+            for (std::size_t i = 0; i + 1 < image.size(); ++i)
+            {
+                if (image[i] == 'Q' && image[i + 1] == 'Z')
+                {
+                    image[i] = 0xC3;
+                    image[i + 1] = 0x28; // an invalid sequence
+                    found = true;
+                }
+            }
+            REQUIRE(found);
+            return image;
+        };
+
+        for (const image_check check :
+                {
+                    image_check::bounds, image_check::none
+                })
+        {
+            // as a value
+            {
+                const json_document loaded = json_document::load(patched(R"(["abQZ"])"), check);
+                json_editable_document e = json_editable_document::parse("[]");
+                CHECK_THROWS_WITH_AS(e.push_back(e.root(), loaded.root()[0]), "[json.exception.type_error.316] invalid UTF-8 byte at index 3: 0x28", json::type_error&);
+                CHECK_THROWS_WITH_AS(e.insert(e.root(), 0, loaded.root()[0]), "[json.exception.type_error.316] invalid UTF-8 byte at index 3: 0x28", json::type_error&);
+                CHECK_THROWS_WITH_AS(e.set(e.root(), loaded.root()[0]), "[json.exception.type_error.316] invalid UTF-8 byte at index 3: 0x28", json::type_error&);
+                CHECK_THROWS_WITH_AS(e.push_back(e.root(), loaded.root()), "[json.exception.type_error.316] invalid UTF-8 byte at index 3: 0x28", json::type_error&);
+                // nothing changed
+                CHECK(e.root().dump() == "[]");
+                CHECK(e.root().size() == 0);
+                CHECK(loaded_dump(e.save()) == "[]");
+                // the valid part of the same document can be copied
+                e.push_back(e.root(), loaded.root().size());
+                CHECK(e.root().dump() == "[1]");
+            }
+            // as a key, and in a nested value
+            {
+                const json_document loaded = json_document::load(patched(R"([{"abQZ": 1}, [["x", "QZ"]]])"), check);
+                json_editable_document e = json_editable_document::parse(R"({"keep": [1]})");
+                CHECK_THROWS_WITH_AS(e.set(e.root(), "k", loaded.root()[0]), "[json.exception.type_error.316] invalid UTF-8 byte at index 3: 0x28", json::type_error&);
+                CHECK_THROWS_WITH_AS(e.set(e.root(), "k", loaded.root()[1]), "[json.exception.type_error.316] invalid UTF-8 byte at index 1: 0x28", json::type_error&);
+                CHECK_THROWS_WITH_AS(e.push_back(e.root()["keep"], loaded.root()[1]), "[json.exception.type_error.316] invalid UTF-8 byte at index 1: 0x28", json::type_error&);
+                CHECK(e.root().dump() == R"({"keep":[1]})");
+                CHECK(loaded_dump(e.save()) == R"({"keep":[1]})");
+            }
+        }
+    }
+#endif
+
     SECTION("the root replaced")
     {
         json_editable_document d = json_editable_document::parse(text);
@@ -530,6 +836,15 @@ TEST_CASE("json_view images: check")
         {
             n.extra = 1; // a hash index
         }), true);
+        // the flag of the targets of links (editable documents) is not part of an image
+        for (std::size_t i = 0; i < node_count(image); ++i)
+        {
+            CAPTURE(i)
+            rejected(corrupted(image, i, [](node & n)
+            {
+                n.flags = static_cast<std::uint8_t>(n.flags | nlohmann::detail::view::node_flags::linked);
+            }), true);
+        }
     }
 
     SECTION("bounds")
@@ -625,7 +940,7 @@ TEST_CASE("json_view images: check")
         });
         CHECK(load_result(as_array, image_check::full).empty());
         const std::string expected_dump = R"({"s":"x\"y","i":-12,"u":7,"f":1.5e+300,"b":true,"n":null,"a":["t",[]]})";
-        CHECK(json_document::load(as_array).root().dump() == expected_dump);
+        CHECK(loaded_dump(as_array) == expected_dump);
     }
 
     SECTION("strings")
@@ -680,7 +995,8 @@ TEST_CASE("json_view images: check")
             n.extra = 0;
         });
         CHECK(load_result(positive, image_check::full).empty());
-        CHECK(json_document::load(positive).root()["u"].is_number_integer());
+        const json_document pos = json_document::load(positive);
+        CHECK(pos.root()["u"].is_number_integer());
         rejected(corrupted(image, 8, [](node & n)
         {
             n.kind = 6; // a float token as integer
@@ -712,6 +1028,136 @@ TEST_CASE("json_view images: check")
         }
     }
 
+    SECTION("float tokens with fewer digits than the layout records")
+    {
+        // The bytes of the token are not digits (they read as zeros or as
+        // other values), so the value has fewer (or more) digits than the
+        // layout says: dump() must still write a number.
+        for (const auto& source : std::vector<std::pair<std::string, std::string>>
+    {
+        {"123456789012345678.5", std::string("@") + std::string(16, '0') + "1.1"}, // 19 digits
+            {"1234.5", "@001.1"},                                                        // 5 digits
+            {"1234.5", "9??.??"}                                                         // more than 5 digits
+        })
+        {
+            CAPTURE(source.second)
+            const std::vector<std::uint8_t> img = json_document::parse("[" + source.first + "]").save();
+            const node n = node_at(img, 1);
+            REQUIRE(source.second.size() == n.len);
+            std::vector<std::uint8_t> b = img;
+            std::memcpy(b.data() + text_at(img) + n.off, source.second.data(), n.len);
+            const json_document d = json_document::load(b, image_check::bounds);
+            const std::string dumped = d.root().dump();
+            CAPTURE(dumped)
+            CHECK(json::parse(dumped)[0].is_number());
+        }
+    }
+
+    SECTION("nodes that share a range")
+    {
+        // [big string, then n strings made to point to the big string]: every
+        // node shares the one range (the check reads it once)
+        const std::size_t n = 200;
+        std::string long_text = "[\"" + std::string(5000, 'a') + "\"";
+        for (std::size_t k = 0; k < n; ++k)
+        {
+            long_text += ",\"x\"";
+        }
+        long_text += "]";
+        const std::vector<std::uint8_t> img = json_document::parse(long_text).save();
+        const node big = node_at(img, 1);
+        std::vector<std::uint8_t> b = img;
+        for (std::size_t k = 0; k < n; ++k)
+        {
+            set_node(b, 2 + k, big);
+        }
+        CHECK(load_result(b, image_check::full).empty());
+        const json_document d = json_document::load(b);
+        CHECK(d.root().size() == n + 1);
+        CHECK(d.root()[n].get<std::string>() == std::string(5000, 'a'));
+        CHECK(d.root().dump() == loaded_dump(b, image_check::none));
+
+        // the same for decoded strings and float tokens, with a node that
+        // records another digit layout than its token
+        const std::vector<std::uint8_t> img2 = json_document::parse(R"(["a\"b", "a\"b", 1.25, 1.25, 1.25e3])").save();
+        CHECK(load_result(img2, image_check::full).empty());
+        std::vector<std::uint8_t> same = img2;
+        set_node(same, 2, node_at(img2, 1));
+        set_node(same, 4, node_at(img2, 3));
+        CHECK(load_result(same, image_check::full).empty());
+        CHECK(loaded_dump(same) == R"(["a\"b","a\"b",1.25,1.25,1250.0])");
+        std::vector<std::uint8_t> layout = same;
+        node f4 = node_at(layout, 4);
+        f4.extra = 0x0100u; // the layout of "1.", and not that of "1.25"
+        set_node(layout, 4, f4);
+        rejected(layout, false);
+        f4.extra = 0xFFFFu; // "many" digits: fine, as compaction writes it
+        set_node(layout, 4, f4);
+        CHECK(load_result(layout, image_check::full).empty());
+    }
+
+    SECTION("ranges that overlap")
+    {
+        // save() writes every string and every token to a place of its own
+        // (nodes that share a value share the whole range): ranges that
+        // overlap without being identical are a damaged image, though each
+        // range is a valid string or token
+        // nodes: 0 [  1 "abcdef"  2 "ghijkl"  3 1.2525  4 9.9  5 "a\"bcd" (decoded)  6 "e\"fgh" (decoded)
+        const std::vector<std::uint8_t> img = json_document::parse(R"(["abcdef", "ghijkl", 1.2525, 9.9, "a\"bcd", "e\"fgh"])").save();
+        REQUIRE(load_result(img, image_check::full).empty());
+        // node i with the range (off of node of + shift, length), and extra
+        const auto aliased = [&](std::size_t i, std::size_t of, std::uint32_t shift, std::uint32_t length, std::uint16_t extra)
+        {
+            std::vector<std::uint8_t> b = img;
+            node n = node_at(b, of);
+            n.off += shift;
+            n.len = length;
+            n.extra = extra;
+            set_node(b, i, n);
+            return b;
+        };
+        // source strings
+        rejected(aliased(2, 1, 0, 4, 0), false);  // "abcd": the start of another string
+        rejected(aliased(2, 1, 1, 4, 0), false);  // "bcde": inside
+        rejected(aliased(2, 1, 2, 4, 0), false);  // "cdef": the end
+        CHECK(load_result(aliased(2, 1, 0, 6, 0), image_check::full).empty()); // the whole range: identical
+        // decoded strings: inside, and partially overlapping (the arena holds a"bcde"fgh)
+        rejected(aliased(6, 5, 1, 3, 0), false);
+        rejected(aliased(6, 5, 3, 5, 0), false);
+        CHECK(load_result(aliased(6, 5, 0, 5, 0), image_check::full).empty());
+        // float tokens: "1.25" and "525" (an integer token as a float) inside "1.2525"
+        rejected(aliased(4, 3, 0, 4, 0x0201u), false);
+        rejected(aliased(4, 3, 3, 3, 0x0003u), false);
+        CHECK(load_result(aliased(4, 3, 0, 6, 0x0401u), image_check::full).empty());
+        // a string and a float token may use the same bytes (each is checked by its own kind)
+        std::vector<std::uint8_t> shared = img;
+        node as_string = node_at(img, 2);
+        as_string.off = node_at(img, 3).off;
+        as_string.len = 6;
+        set_node(shared, 2, as_string);
+        CHECK(load_result(shared, image_check::full).empty());
+        // empty strings inside others are not ranges
+        CHECK(load_result(aliased(2, 1, 2, 0, 0), image_check::full).empty());
+    }
+
+    SECTION("copies within an edited document")
+    {
+        // copies within a document share the value: identical ranges
+        json_editable_document d = json_editable_document::parse(R"({"s": "ab", "e": "x\"y", "f": 1.5, "g": 1.5e300, "a": [1.5, "ab"]})");
+        d.set(d.root(), "c1", d.root()["a"]);
+        d.set(d.root(), "c2", d.root()["a"]);
+        d.set(d.root(), "c3", d.root());
+        d.push_back(d.root()["a"], d.root()["e"]);
+        d.push_back(d.root()["a"], d.root()["g"]);
+        d.push_back(d.root()["a"], d.root()["g"]);
+        d.set(d.root()["s"], "changed");
+        d.set(d.root()["f"], 7.25);
+        const std::vector<std::uint8_t> saved = d.save();
+        CHECK(load_result(saved, image_check::full).empty());
+        CHECK(loaded_dump(saved) == d.root().dump());
+        check_round_trip(d);
+    }
+
     SECTION("integer ranges")
     {
         // tokens of many digits, which the parser stores as floats

tests/src/unit-to_chars.cpp

@@ -15,6 +15,7 @@
 #include <nlohmann/json.hpp>
 using nlohmann::detail::dtoa_impl::reinterpret_bits;
 
+#include <algorithm>
 #include <array>
 #include <cmath>
 #include <cstdint>
@@ -666,13 +667,24 @@ void check_shortest(double v)
     const std::string text(buf.data(), end);
     CAPTURE(text)
     CHECK(parse_double(text) == v);
-    // the layout is that of format_buffer() for the same digits
+    // the layout is that of format_buffer() for the digits of Zmij
+    const auto sd = nlohmann::detail::zmij::to_shortest(reinterpret_bits<std::uint64_t>(v));
+    const std::uint64_t significand = sd.has_digit ? (sd.integral * 10) + sd.digit : sd.integral;
+    int exponent = sd.has_digit ? sd.exponent : sd.exponent + 1;
+    std::string significand_digits = std::to_string(significand);
+    while (significand_digits.size() > 1 && significand_digits.back() == '0')
+    {
+        significand_digits.pop_back();
+        ++exponent;
+    }
     std::array<char, 64> reference{};
-    int len = 0;
-    int exponent = 0;
-    nlohmann::detail::dtoa_impl::shortest_digits(reference.data(), len, exponent, v);
-    const char* const reference_end = nlohmann::detail::dtoa_impl::format_buffer(reference.data(), len, exponent, -4, 15);
+    std::copy(significand_digits.begin(), significand_digits.end(), reference.begin());
+    const char* const reference_end = nlohmann::detail::dtoa_impl::format_buffer(reference.data(), static_cast<int>(significand_digits.size()), exponent, -4, 15);
     CHECK(text == std::string(reference.data(), static_cast<std::size_t>(reference_end - reference.data())));
+    // and write_positive() is what to_chars() calls
+    std::array<char, 64> positive{};
+    const char* const positive_end = nlohmann::detail::dtoa_impl::write_positive(positive.data(), positive.data() + positive.size(), v);
+    CHECK(text == std::string(positive.data(), static_cast<std::size_t>(positive_end - positive.data())));
     const auto de = digits_and_exponent(text);
     const std::string& digits = de.first;
     if (digits.size() > 1)
@@ -785,3 +797,140 @@ TEST_CASE("shortest digits of doubles")
         }
     }
 }
+
+TEST_CASE("choice of the conversion")
+{
+    using nlohmann::detail::dtoa_impl::is_binary64;
+
+    SECTION("by the format of the type")
+    {
+        // Zmij needs binary64 numbers; everything else uses Grisu2
+        static_assert(!is_binary64<float>::value, "float is not binary64");
+        static_assert(is_binary64<double>::value == (std::numeric_limits<double>::is_iec559 && std::numeric_limits<double>::digits == 53),
+                      "double is binary64 where it is IEEE 754 with 53 digits");
+        static_assert(!is_binary64<int>::value, "integers are not binary64");
+        static_assert(is_binary64<long double>::value == (std::numeric_limits<long double>::is_iec559 && std::numeric_limits<long double>::digits == 53 && sizeof(long double) == 8),
+                      "long double is binary64 where it has the format of a double");
+        CHECK(!is_binary64<float>::value);
+        CHECK(is_binary64<double>::value);
+    }
+
+    SECTION("float: Grisu2, double: Zmij")
+    {
+        // 5.3165205877497296e+16 is one of the doubles for which Grisu2 does not find the shortest digits
+        constexpr double value = 5.3165205877497296e+16;
+        std::array<char, 64> buf{};
+        const char* const last = buf.data() + buf.size();
+
+        char* end = nlohmann::detail::dtoa_impl::write_positive(buf.data(), last, value);
+        CHECK(std::string(buf.data(), end) == "5.31652058774973e+16");
+        end = nlohmann::detail::dtoa_impl::write_positive_grisu2(buf.data(), last, value);
+        CHECK(std::string(buf.data(), end) == "5.3165205877497296e+16");
+
+        constexpr float f = 1.1754944e-38f;
+        end = nlohmann::detail::dtoa_impl::write_positive(buf.data(), last, f);
+        const std::string dispatched(buf.data(), end);
+        end = nlohmann::detail::dtoa_impl::write_positive_grisu2(buf.data(), last, f);
+        CHECK(dispatched == std::string(buf.data(), end));
+    }
+
+    SECTION("long double with the format of a double: Zmij")
+    {
+        // (on platforms where long double is wider, Grisu2 does not apply either: the snprintf fallback does)
+        if (std::numeric_limits<long double>::digits == 53 && std::numeric_limits<long double>::is_iec559)
+        {
+            using long_double_json = nlohmann::json::with_float_t<long double>;
+            for (const double d :
+                    {
+                        5.3165205877497296e+16, 1.0, 0.1, 123456.789, 2.2250738585072014e-308, 1.7976931348623157e+308, -5.3165205877497296e+16
+                    })
+            {
+                CAPTURE(d)
+                CHECK(long_double_json(static_cast<long double>(d)).dump() == nlohmann::json(d).dump());
+            }
+            CHECK(long_double_json(5.3165205877497296e+16L).dump() == "5.31652058774973e+16");
+        }
+    }
+}
+
+TEST_CASE("short decimals")
+{
+    // write_short_decimal() writes digits * 10^exp for the digits of a double
+    // that need no conversion (at most 15, the first not 0): as to_chars()
+    // writes the (positive) double that has these digits
+    const auto written = [](std::uint64_t digits, int exp)
+    {
+        std::array<char, 64> buf{}; // (up to 41 bytes are written)
+        char* const end = nlohmann::detail::dtoa_impl::write_short_decimal(buf.data(), digits, exp);
+        return std::string(buf.data(), end);
+    };
+    const auto written_counted = [](std::uint64_t digits, int count, int exp)
+    {
+        std::array<char, 64> buf{};
+        char* const end = nlohmann::detail::dtoa_impl::write_short_decimal(buf.data(), digits, count, exp);
+        return std::string(buf.data(), end);
+    };
+    const auto expected = [](std::uint64_t digits, int exp)
+    {
+        const double value = std::strtod((std::to_string(digits) + "e" + std::to_string(exp)).c_str(), nullptr);
+        std::array<char, 64> buf{};
+        char* const end = nlohmann::detail::to_chars(buf.data(), buf.data() + 32, value);
+        return std::string(buf.data(), end);
+    };
+
+    SECTION("powers of ten")
+    {
+        const auto& powers = nlohmann::detail::dtoa_impl::powers_of_ten_16();
+        std::uint64_t power = 1;
+        for (const std::uint64_t p : powers)
+        {
+            CHECK(p == power);
+            power *= 10;
+        }
+    }
+
+    SECTION("examples")
+    {
+        CHECK(written(1, 0) == "1.0");
+        CHECK(written(15, -1) == "1.5");
+        CHECK(written(125, -2) == "1.25");
+        CHECK(written(1, 22) == "1e+22");
+        CHECK(written(123456789012345, -2) == "1234567890123.45");
+        CHECK(written(999999999999999, -15) == "0.999999999999999");
+        CHECK(written(5, -324) == "5e-324");
+        CHECK(written_counted(1, 1, 0) == "1.0");
+        CHECK(written_counted(125, 3, -2) == "1.25");
+        CHECK(written_counted(100, 3, -2) == "1.0");
+        CHECK(written_counted(999999999999999, 15, -15) == "0.999999999999999");
+    }
+
+    SECTION("random digits, exponents and trailing zeros")
+    {
+        std::mt19937_64 rng(1170); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        for (int i = 0; i < 100000; ++i)
+        {
+            // 1 to 15 digits, the first not 0, and up to 14 of them trailing zeros
+            std::uint64_t count = 1 + (rng() % 15u);
+            std::uint64_t power = 1;
+            for (std::uint64_t k = 1; k < count; ++k)
+            {
+                power *= 10;
+            }
+            std::uint64_t digits = power + (rng() % (9 * power));
+            const std::uint64_t zeros = (rng() % 3u == 0) ? (rng() % count) : 0;
+            for (std::uint64_t k = 0; k < zeros; ++k)
+            {
+                digits = (digits / 10) * 10;
+            }
+            // (a value between 1e-300 and 1e300)
+            const int exp = static_cast<int>(rng() % 560u) - 300 - static_cast<int>(count);
+
+            CAPTURE(digits)
+            CAPTURE(count)
+            CAPTURE(exp)
+            const std::string want = expected(digits, exp);
+            CHECK(written(digits, exp) == want);
+            CHECK(written_counted(digits, static_cast<int>(count), exp) == want);
+        }
+    }
+}