Regenerate the amalgamated headers

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

.github/labeler.yml

@@ -63,12 +63,12 @@ labels:
     - "single_include/nlohmann/json_view\\.hpp"
     - "tests/src/unit-json_view.*"
     - "tests/src/json_view_test_helpers\\.hpp"
-    - "tests/src/fuzzer-parse_json_view\\.cpp"
+    - "tests/src/fuzzer-(parse_json_view|json_view_image)\\.cpp"
     - "tools/amalgamate/config_json_view\\.json"
     - "docs/mkdocs/docs/features/json_view\\.md"
     - "docs/mkdocs/docs/api/basic_json_(document|view)/.*"
-    - "docs/mkdocs/docs/api/(ordered_)?json_(document|view)\\.md"
-    - "docs/mkdocs/docs/examples/(basic_json_(document|view)__|(ordered_)?json_(document|view)).*"
+    - "docs/mkdocs/docs/api/(ordered_)?json_(editable_)?(document|view)\\.md"
+    - "docs/mkdocs/docs/examples/(basic_json_(document|view)__|(ordered_)?json_(editable_)?(document|view)).*"
     - "tests/benchmarks/src/benchmarks_view\\.cpp"
 
 - label: "aspect: json_view"

BUILD.bazel

@@ -70,7 +70,10 @@ cc_library(
         "include/nlohmann/detail/view/builder.hpp",
         "include/nlohmann/detail/view/compare.hpp",
         "include/nlohmann/detail/view/document_data.hpp",
+        "include/nlohmann/detail/view/edit.hpp",
+        "include/nlohmann/detail/view/edit_storage.hpp",
         "include/nlohmann/detail/view/errors.hpp",
+        "include/nlohmann/detail/view/image.hpp",
         "include/nlohmann/detail/view/input.hpp",
         "include/nlohmann/detail/view/iterator.hpp",
         "include/nlohmann/detail/view/lookup.hpp",

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

@@ -0,0 +1,128 @@
+# <small>nlohmann::basic_json_document::</small>erase
+
+```cpp
+// (1)
+std::size_t erase(view_type object, string_view_t key);
+
+// (2)
+template<typename I>
+void erase(view_type array, I idx);
+
+// (3)
+std::size_t erase(const json_pointer& ptr);
+```
+
+Only an **editable** document (`#!cpp Editable == true`, e.g. [`json_editable_document`](../json_editable_document.md))
+has `erase`; calling it on a read-only `basic_json_document` fails to compile (`#!cpp static_assert`).
+
+1. Removes every member of `object` whose key is `key` (see [Notes](#notes) on duplicate keys) and returns how many
+   were removed; `#!cpp 0` if `object` has no member with this key.
+2. Removes the element at index `idx` of `array`, which must already exist (`#!cpp idx < array.size()`).
+3. Removes the value the JSON pointer `ptr` refers to, relative to [`root()`](root.md), and returns how many values
+   were removed: the *parent* of the target must already exist, and the target itself is removed as in 1. (an object
+   member; `#!cpp 0` or more) or 2. (an array element; always `#!cpp 1`). `ptr` must not be empty -- [`root()`](root.md)
+   itself cannot be erased.
+
+## Template parameters
+
+`I`
+:   an integral type other than `#!cpp bool`, deduced (overloads taking a `#!cpp bool` or a non-integral type for
+    `idx` do not participate in overload resolution).
+
+## Parameters
+
+`object` (in)
+:   the object to remove a member of
+
+`array` (in)
+:   the array to remove an element of
+
+`key` (in)
+:   the key of the member(s) to remove
+
+`idx` (in)
+:   the index of the element to remove; a negative value throws (see [Exceptions](#exceptions))
+
+`ptr` (in)
+:   a JSON pointer to the value to remove, relative to `root()`
+
+## Return value
+
+1. the number of removed members (`#!cpp 0` if `object` had none with this `key`)
+2. (nothing)
+3. the number of removed values (`#!cpp 0` or more for an object member, always `#!cpp 1` for an array element)
+
+## Exceptions
+
+1. Throws [`type_error.307`](../../home/exceptions.md#jsonexceptiontype_error307) if `object` is not an object -- the
+   same message [`BasicJsonType::erase`](../basic_json/erase.md) throws for the same type.
+2. Throws `type_error.307` if `array` is not an array. Throws
+   [`out_of_range.401`](../../home/exceptions.md#jsonexceptionout_of_range401) if `idx` is negative, or if
+   `#!cpp idx >= array.size()`.
+3. Throws [`out_of_range.405`](../../home/exceptions.md#jsonexceptionout_of_range405) ("JSON pointer has no parent")
+   if `ptr` is empty. Throws what [`at`](../basic_json_view/at.md) throws (overload 3) for resolving `ptr`'s parent.
+   For the last reference token itself: if the parent is an array, throws what 2. throws for an index that is out of
+   range, or, for a token that is not a valid array index,
+   [`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); otherwise (an
+   object, or a primitive value the pointer's parent resolves to) throws what 1. throws.
+
+Every overload also throws [`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202) ("view
+does not belong to this document") if `object`/`array` is a [discarded](../basic_json_view/is_discarded.md) view or a
+view of a *different* document (overloads 1-2 only; overload 3 always starts from this document's own
+[`root()`](root.md)).
+
+## Complexity
+
+1. Linear in the number of members of `object`.
+2. Linear in the number of elements of `array` at or after `idx` (they move one slot over).
+3. Linear in the number of reference tokens of `ptr` and, for each token, in the number of members of the object at
+   that level or the index into the array (as [`at`](../basic_json_view/at.md)), plus the complexity of 1. or 2. for
+   the last token.
+
+## Notes
+
+!!! 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
+    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
+referring to a removed member or element keeps showing what it last held (see [Edits](index.md#edits)) -- it just no
+longer appears when `array`/`object` is read, dumped, or iterated. Removing an element of `array` (2.) does shift the
+*links* to the elements after it, the same way `insert`, `set`, or `push_back` on the same array would; any iterator
+already taken over `array`/`object` is invalidated by an erase, since it was walking the old layout.
+
+## Examples
+
+??? example
+
+    The example below drops a deprecated field and a decommissioned entry from a configuration document -- using all
+    three overloads -- and shows what stays intact that would not with a plain `json`/`ordered_json` value: the order
+    of the fields around the ones removed, and the exact spelling of a number that was never touched.
+
+    ```cpp
+    --8<-- "examples/basic_json_document__erase.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/basic_json_document__erase.output"
+    ```
+
+## See also
+
+- [insert](insert.md) - insert an element into an array
+- [set](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers to
+- [push_back](push_back.md) - append to an array
+- [root](root.md) - the view of the root value, the starting point of overload 3
+- [`BasicJsonType::erase`](../basic_json/erase.md) - the corresponding function of `basic_json`
+- [Edits](index.md#edits) - what an edit guarantees, for every overload
+
+## Version history
+
+- Added in version 3.13.0.

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

@@ -3,7 +3,7 @@
 <small>Defined in header `<nlohmann/json_view.hpp>`</small>
 
 ```cpp
-template<typename BasicJsonType>
+template<typename BasicJsonType, bool Editable = false>
 class basic_json_document;
 ```
 
@@ -20,6 +20,11 @@ is move-only: a copy would duplicate the whole index, the decoded-string buffer,
 enough in every use we know of. The index, the decoded strings, and the owned text live in one heap block that the
 document holds through a `#!cpp std::unique_ptr`; this is also why views survive a move of the document.
 
+With `#!cpp Editable == true`, the document also offers [`set`](set.md), [`push_back`](push_back.md),
+[`insert`](insert.md), and [`erase`](erase.md) to change values in place, see [Edits](#edits) below. The source text
+itself is never written; a read-only document (`#!cpp Editable == false`, the default) does not carry any of the
+bookkeeping edits need, and calling any of them on one fails to compile (`#!cpp static_assert`).
+
 ## Template parameters
 
 `BasicJsonType`
@@ -27,23 +32,38 @@ document holds through a `#!cpp std::unique_ptr`; this is also why views survive
     [`ordered_json`](../ordered_json.md). Only 64-bit `number_integer_t`/`number_unsigned_t` types are supported; this
     is checked with a `static_assert`.
 
+`Editable`
+:   whether the document supports [`set`](set.md), [`push_back`](push_back.md), [`insert`](insert.md), and
+    [`erase`](erase.md) (optional, `#!cpp false` by default). See [Edits](#edits) below.
+
 ## Specializations
 
-- [**json_document**](../json_document.md) - documents of the default specialization [`json`](../json.md)
-- [**ordered_json_document**](../ordered_json_document.md) - documents of [`ordered_json`](../ordered_json.md)
+- [**json_document**](../json_document.md) - read-only documents of the default specialization [`json`](../json.md)
+- [**ordered_json_document**](../ordered_json_document.md) - read-only documents of
+  [`ordered_json`](../ordered_json.md)
+- [**json_editable_document**](../json_editable_document.md) - editable documents of [`json`](../json.md)
+- [**ordered_json_editable_document**](../ordered_json_editable_document.md) - editable documents of
+  [`ordered_json`](../ordered_json.md)
 
 ## Member types
 
-- **view_type** - the type of view returned by [`root()`](root.md) (`#!cpp basic_json_view<BasicJsonType>`)
+- **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
 
 - [(constructor)](basic_json_document.md)
+
+### Parsing
+
 - [**parse**](parse.md) (_static_) - deserialize from a compatible input, borrowing or owning it as appropriate
 - [**parse_copy**](parse_copy.md) (_static_) - deserialize a copy of a compatible input
 - [**accept**](accept.md) (_static_) - check whether the input is valid JSON
 - [**read**](read.md) - (re-)parse into this document, reusing its memory
+
+### Access
+
 - [**root**](root.md) - the view of the root value
 - [**is_discarded**](is_discarded.md) - return whether the last parse failed
 - [**source**](source.md) - the parsed text
@@ -52,6 +72,49 @@ document holds through a `#!cpp std::unique_ptr`; this is also why views survive
 - [**memory_usage**](memory_usage.md) - the number of bytes held by the document
 - [**shrink_to_fit**](shrink_to_fit.md) - release unused index capacity
 
+### Images
+
+- [**save**](save.md) - the document as an image that `load()` reads without parsing
+- [**load**](load.md) (_static_) - read an image written by `save()`
+
+### Edits
+
+- [**set**](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers
+  to (`#!cpp Editable` documents only)
+- [**push_back**](push_back.md) - append to an array (`#!cpp Editable` documents only)
+- [**insert**](insert.md) - insert an element into an array before a given position (`#!cpp Editable` documents only)
+- [**erase**](erase.md) - remove an object member, an array element, or the value a JSON pointer refers to
+  (`#!cpp Editable` documents only)
+
+## Edits
+
+An editable document (`#!cpp Editable == true`) can be changed after parsing, with [`set`](set.md),
+[`push_back`](push_back.md), [`insert`](insert.md), and [`erase`](erase.md);
+[`json_editable_document`](../json_editable_document.md) and
+[`ordered_json_editable_document`](../ordered_json_editable_document.md) are the corresponding specializations. A few
+points apply to every edit:
+
+- **The source text is never written**, and the parsed index never moves: every value keeps the node it was parsed
+  into, so [views](../basic_json_view/index.md) taken before an edit stay valid, including
+  [`root()`](root.md). New values (and the element sequences of an edited array/object) go to storage owned by the
+  document, allocated on demand.
+- **A view keeps referring to the same value.** After [`set`](set.md) replaces the value a view refers to, that view
+  sees the new value; a view of a value that a later edit replaces or drops keeps showing what it last held. An edit
+  of an array or object, however, **invalidates the iterators taken over it** (its members may now live in a
+  different sequence), and a string obtained with [`get_string()`](../basic_json_view/get_string.md) stays valid even
+  as further edits happen (earlier buffers of edited text are kept alive, not overwritten).
+- **Values are accepted three ways:** a [`basic_json_view`](../basic_json_view/index.md) of *any* document
+  (read-only or editable; it is copied, nothing is shared with the source document), a `BasicJsonType` value, or
+  anything `BasicJsonType` can be constructed from (numbers, strings, `#!cpp bool`, `#!cpp nullptr`, containers, ...).
+- [`dump()`](../basic_json_view/dump.md) writes an edited document with members in document order, new members at
+  the end, and, with [`number_format::source`](../basic_json_view/number_format.md), keeps the spelling of every
+  number that was not itself edited -- see [Editing a document](../../features/json_view.md#editing-a-document) for
+  why this matters.
+- [`read()`](read.md) discards all edits, [`shrink_to_fit()`](shrink_to_fit.md) does not move the node index once
+  there are edits, and [`memory_usage()`](memory_usage.md) includes the memory edits use.
+  [`source_offset()`](../basic_json_view/source_offset.md) of a value introduced by an edit is
+  `#!cpp static_cast<std::size_t>(-1)`, the same value it reports for a decoded string.
+
 ## Version history
 
 - Added in version 3.13.0.

docs/mkdocs/docs/api/basic_json_document/insert.md

@@ -0,0 +1,114 @@
+# <small>nlohmann::basic_json_document::</small>insert
+
+```cpp
+template<typename I, typename V>
+view_type insert(view_type array, I idx, V&& value);
+```
+
+Only an **editable** document (`#!cpp Editable == true`, e.g. [`json_editable_document`](../json_editable_document.md))
+has `insert`; calling it on a read-only `basic_json_document` fails to compile (`#!cpp static_assert`).
+
+Inserts `value` into `array` as a new element before position `idx`, which must not be past the end
+(`#!cpp idx <= array.size()`; `#!cpp idx == array.size()` appends, like [`push_back`](push_back.md)). Unlike
+[`push_back`](push_back.md), a [null](../basic_json_view/is_null.md) `array` does *not* first become an empty array:
+`array` must already be an array.
+
+`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 `array`'s own document -- which is copied so that nothing is shared with the
+source document afterward; a `BasicJsonType` value; or anything `BasicJsonType` can be constructed from (numbers,
+strings, `#!cpp bool`, `#!cpp nullptr`, containers, ...).
+
+## Template parameters
+
+`I`
+:   an integral type other than `#!cpp bool`, deduced (overloads taking a `#!cpp bool` or a non-integral type for
+    `idx` do not participate in overload resolution).
+
+`V`
+:   the type of `value`, deduced; see above for what is accepted.
+
+## Parameters
+
+`array` (in)
+:   the array to insert into
+
+`idx` (in)
+:   the position to insert `value` before; a negative value throws (see [Exceptions](#exceptions))
+
+`value` (in)
+:   the value to insert
+
+## Return value
+
+a view of the new element, now holding `value`
+
+## Exception safety
+
+Basic exception safety: `value` is fully encoded -- including the checks below -- into storage owned by the document
+before anything already reachable from [`root()`](root.md) is touched, so a failure while encoding `value` (an
+invalid argument, or `#!cpp std::bad_alloc`) leaves the document completely unchanged, other than memory allocated
+for the encoding that is not reclaimed. A failure of a later allocation -- while `array` switches from its parsed
+layout to a growable block, or while that block grows, see [Notes](#notes) -- can still leave `array` already
+switched to that layout even though `value` itself was not inserted.
+
+## Exceptions
+
+Throws [`type_error.309`](../../home/exceptions.md#jsonexceptiontype_error309) if `array` is not an array -- the same
+message [`BasicJsonType::insert`](../basic_json/insert.md) throws for the same type; a null `array` throws this too
+(see above). Throws [`out_of_range.401`](../../home/exceptions.md#jsonexceptionout_of_range401) if `idx` is negative,
+or if `#!cpp idx > array.size()`. Throws
+[`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202) ("view does not belong to this
+document") if `array` is a [discarded](../basic_json_view/is_discarded.md) view or a view of a *different* document.
+Throws [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) if `value` is a
+[discarded](../basic_json_view/is_discarded.md) view or a [discarded](../basic_json/is_discarded.md) `BasicJsonType`
+value, and [`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. Throws
+[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) if `value` is (or contains) a string that is
+not valid UTF-8, with the same message [`BasicJsonType::dump()`](../basic_json/dump.md) gives for that string.
+
+## Complexity
+
+Linear in the number of elements of `array` at or after `idx` (they move one slot over), plus time linear in the
+size of `value` to encode it into the document's storage (constant for a scalar, linear in the number of nested
+values for an array or object): like [`push_back`](push_back.md), the elements of `array` move to a growable block
+of links the first time it is inserted into (or [`set`](set.md)/[`push_back`](push_back.md) on), and that block
+grows in amortized constant time; inserting before the end within that block still shifts every later element.
+
+## Notes
+
+Like [`set`](set.md) on a member or an element, `insert` never moves an existing *element's value* -- only where
+`array`'s *links* to its elements live -- so a view of an existing element of `array` stays valid across an
+`insert`, and keeps referring to the same element even though its index shifts. Any iterator already taken over
+`array` is invalidated, since it was walking the old layout. See [Edits](index.md#edits) for what stays valid across
+an edit in general.
+
+## Examples
+
+??? example
+
+    The example below inserts a step into the middle of a deployment plan, without touching the steps that come
+    after it, and shows that a view taken before the insert keeps referring to the same element even though its
+    index shifts -- something a plain `json`/`ordered_json` array, or its `std::vector`-based storage, has no
+    equivalent for.
+
+    ```cpp
+    --8<-- "examples/basic_json_document__insert.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/basic_json_document__insert.output"
+    ```
+
+## See also
+
+- [push_back](push_back.md) - append to an array
+- [erase](erase.md) - remove an object member, an array element, or the value a JSON pointer refers to
+- [set](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers to
+- [`BasicJsonType::insert`](../basic_json/insert.md) - the corresponding function of `basic_json`
+- [Edits](index.md#edits) - what an edit guarantees, for every overload
+
+## Version history
+
+- Added in version 3.13.0.

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

@@ -0,0 +1,176 @@
+# <small>nlohmann::basic_json_document::</small>load
+
+```cpp
+// (1)
+static basic_json_document load(const std::uint8_t* image, std::size_t size,
+                                 const image_check check = image_check::full);
+
+// (2)
+static basic_json_document load(const std::vector<std::uint8_t>& image,
+                                 const image_check check = image_check::full);
+
+// (3)
+static basic_json_document load(std::vector<std::uint8_t>&& image,
+                                 const image_check check = image_check::full);
+```
+
+1. Reads an image [`save()`](save.md) wrote, from a pointer and a byte count. The image is **borrowed**: `image`
+   must stay alive and unchanged for as long as the returned document, and any view taken from it, is used.
+2. Reads an image from a `#!cpp std::vector`. Also **borrowed** -- equivalent to overload 1 called with
+   `#!cpp image.data()` and `#!cpp image.size()`.
+3. Reads an image, keeping the vector instead of copying it: `image` is moved into the document (no copy), which
+   then owns it for as long as it needs the text and the decoded strings. [`owns_source()`](owns_source.md) is
+   `#!cpp true` afterward.
+
+In every overload, the node index is copied into storage the document itself owns -- so that it is properly aligned,
+and, for an [editable](index.md#edits) document, can be edited -- while the text and the decoded strings stay in
+`image`. The hash indexes [large objects](../../features/json_view.md) use for lookup are rebuilt, exactly as after
+parsing.
+
+## Parameters
+
+`image` (in)
+:   the image [`save()`](save.md) wrote (overloads 1 and 2), or one to take ownership of (overload 3)
+
+`size` (in)
+:   the number of bytes at `image` (overload 1)
+
+`check` (in)
+:   how thoroughly to validate `image` before trusting it; see [`image_check`](#image_check) below (optional,
+    `#!cpp image_check::full` by default)
+
+## Return value
+
+The document read from the image.
+
+## Exception safety
+
+Overloads 1 and 2 give the strong guarantee: `image` is only read, never written, so a thrown exception leaves the
+caller's buffer untouched.
+
+Overload 3 moves `image` into the document *before* validating it, so that a good image is kept without a copy. If
+loading then fails, the partially built document -- and the vector now inside it -- is discarded along with the
+exception, and `image` itself is left **empty**, not restored to what was passed in. Move a copy in instead, or
+validate with overload 2 first, if the original vector must survive a failed load.
+
+## Exceptions
+
+On a big-endian target, throws [`type_error.320`](../../home/exceptions.md#jsonexceptiontype_error320) -- the same
+exception [`save()`](save.md#exceptions) throws there, since the image format is little-endian only.
+
+Otherwise throws [`parse_error.116`](../../home/exceptions.md#jsonexceptionparse_error116) if `image` is not one
+`save()` could have written, or fails the requested `check`:
+
+| message               | when                                                                                                |
+|------------------------|------------------------------------------------------------------------------------------------------|
+| `too short`            | `image` is `#!cpp nullptr`, or `size` is smaller than the 64-byte header                             |
+| `unknown format`       | the header's magic bytes or version do not match, or a reserved header field is not zero             |
+| `sizes out of range`   | the node count, text size, or decoded-string size the header describes does not fit `size`, or the `#!cpp '\0'` after the text or after the decoded strings is missing |
+| `the check failed`     | `check` is not `#!cpp image_check::none`, and the image fails it -- see [`image_check`](#image_check) |
+
+!!! failure "Example messages"
+
+    ```
+    [json.exception.parse_error.116] parse error: invalid json_document image: too short
+    ```
+    ```
+    [json.exception.parse_error.116] parse error: invalid json_document image: unknown format
+    ```
+    ```
+    [json.exception.parse_error.116] parse error: invalid json_document image: sizes out of range
+    ```
+    ```
+    [json.exception.parse_error.116] parse error: invalid json_document image: the check failed
+    ```
+
+## Complexity
+
+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
+
+### `image_check` { #image_check }
+
+```cpp
+using image_check = detail::view::image_check;
+
+enum class image_check
+{
+    full,
+    bounds,
+    none
+};
+```
+
+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; 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 |
+
+`full` is the default and the right choice for an image from anything you do not fully control -- a file, a cache
+shared with other processes, a peer on the network. `bounds` skips scanning the text and the decoded strings, so it
+fits a cache your own process just wrote and reads straight back, where damage would mean a bug or a hardware fault
+rather than adversarial input; it still cannot crash or read out of bounds. `none` skips validation entirely and
+should only be used for an image you trust as much as your own memory.
+
+**Lifetime.** Overloads 1 and 2 borrow `image`: it must stay alive and byte-for-byte unchanged for as long as the
+returned document, and any [view](../basic_json_view/index.md) taken from it, is used -- exactly like a document
+[`parse()`](parse.md) borrowed its input for. Overload 3 avoids this by keeping the vector itself; see
+[`owns_source`](owns_source.md).
+
+!!! warning "Experimental"
+
+    The image format is versioned but not yet stable, and may change in an incompatible way before it is declared
+    stable; `load()` already rejects an image written by a different format version with `parse_error.116`
+    ("unknown format"). Use images to cache a document within one build of the library, or to hand one to another
+    process running the *same* build on the *same* (little-endian) machine -- not as a long-term storage format.
+
+**What `image_check::bounds` does not guarantee.** A bounds-checked image can never make `load()`,
+[`root()`](root.md), element access, or [`materialize()`](../basic_json_view/materialize.md) read outside the image,
+so those stay safe on a damaged one. It does *not* guarantee that the image describes valid JSON: a string
+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
+
+??? example "Caching a document, ownership, and a rejected image"
+
+    The example below saves a parsed document as an image, checks that `load()` reproduces the original
+    [`dump()`](../basic_json_view/dump.md) without parsing, and shows the difference between
+    `load(std::move(image))` (owned) and `load(image)` (borrowed). It then damages one byte of the image and shows
+    `image_check::full` rejecting it with `parse_error.116`, while `image_check::bounds` -- meant for a cache the
+    process already trusts -- still reads it without going out of bounds.
+
+    ```cpp
+    --8<-- "examples/basic_json_document__load.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/basic_json_document__load.output"
+    ```
+
+## See also
+
+- [save](save.md) - write the document as an image
+- [owns_source](owns_source.md) - return whether the document holds its own copy of the text
+- [parse](parse.md) - deserialize from JSON text instead of an image
+- [Images](../../features/json_view.md#images) - why and when to use images
+
+## Version history
+
+- Added in version 3.13.0.

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

@@ -149,6 +149,7 @@ buffer of a given length, pass a pair of pointers: `#!cpp parse(ptr, ptr + len)`
 - [accept](accept.md) - check whether the input is valid JSON
 - [read](read.md) - (re-)parse into this document, reusing its memory
 - [owns_source](owns_source.md) - return whether the document holds its own copy of the text
+- [load](load.md) - read a document from an image instead of parsing JSON text
 - [`BasicJsonType::parse`](../basic_json/parse.md) - the corresponding function of `basic_json`
 
 ## Version history

docs/mkdocs/docs/api/basic_json_document/push_back.md

@@ -0,0 +1,102 @@
+# <small>nlohmann::basic_json_document::</small>push_back
+
+```cpp
+template<typename V>
+view_type push_back(view_type array, V&& value);
+```
+
+Appends `value` as a new last element of `array`. A [null](../basic_json_view/is_null.md) `array` first becomes an
+empty array, the same way [`set`](set.md) turns a null `object` into an empty object.
+
+`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 `array`'s own document -- which is copied so that nothing is shared with the
+source document afterward; a `BasicJsonType` value; or anything `BasicJsonType` can be constructed from (numbers,
+strings, `#!cpp bool`, `#!cpp nullptr`, containers, ...).
+
+Only an **editable** document (`#!cpp Editable == true`, e.g. [`json_editable_document`](../json_editable_document.md))
+has `push_back`; calling it on a read-only `basic_json_document` fails to compile (`#!cpp static_assert`).
+
+## Template parameters
+
+`V`
+:   the type of `value`, deduced; see above for what is accepted.
+
+## Parameters
+
+`array` (in)
+:   the array (or null value) to append to
+
+`value` (in)
+:   the value to append
+
+## Return value
+
+a view of the new last element of `array`, now holding `value`
+
+## Exception safety
+
+Basic exception safety: `value` is fully encoded -- including the checks below -- into storage owned by the document
+before anything already reachable from [`root()`](root.md) is touched, so a failure while encoding `value` (an
+invalid argument, or `#!cpp std::bad_alloc`) leaves the document completely unchanged, other than memory allocated
+for the encoding that is not reclaimed. A failure of a later allocation -- while `array` switches from its parsed
+layout to a growable block, or while that block grows, see [Notes](#notes) -- can still leave a partial effect, such
+as a null `array` argument already turned into an empty array even though `value` itself was not appended.
+
+## Exceptions
+
+Throws [`type_error.308`](../../home/exceptions.md#jsonexceptiontype_error308) if `array` is neither an array nor
+null -- the same message [`BasicJsonType::push_back`](../basic_json/push_back.md) throws for the same type. Throws
+[`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202) ("view does not belong to this
+document") if `array` is a [discarded](../basic_json_view/is_discarded.md) view or a view of a *different* document.
+Throws [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) if `value` is a
+[discarded](../basic_json_view/is_discarded.md) view or a [discarded](../basic_json/is_discarded.md) `BasicJsonType`
+value, and [`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. Throws
+[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) if `value` is (or contains) a string that is
+not valid UTF-8, with the same message [`BasicJsonType::dump()`](../basic_json/dump.md) gives for that string.
+
+## Complexity
+
+Amortized constant, plus time linear in the size of `value` to encode it into the document's storage (constant for
+a scalar, linear in the number of nested values for an array or object): the elements of `array` move to a growable
+block of links the first time it is appended to (or [`set`](set.md) on), and that block itself grows -- doubling its
+capacity, so the cost of growing it amortizes to constant per element -- only once it runs out of room. See
+[Notes](#notes).
+
+## Notes
+
+Like [`set`](set.md) on a member or an element, `push_back` never moves an existing element itself -- only where
+`array`'s *links* to its elements live -- so a view of an existing element of `array` stays valid across a
+`push_back`, but any iterator already taken over `array` is invalidated, since it was walking the old layout. See
+[Edits](index.md#edits) for what stays valid across an edit in general.
+
+## Examples
+
+??? example
+
+    The example below appends records to an array one at a time, as they might arrive from a stream of events,
+    without ever building a `BasicJsonType` value for the array or for the records already in it, and shows that a
+    view taken from an earlier `push_back` still refers to the same element once later ones have run.
+
+    ```cpp
+    --8<-- "examples/basic_json_document__push_back.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/basic_json_document__push_back.output"
+    ```
+
+## See also
+
+- [set](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers to
+- [insert](insert.md) - insert an element into an array before a given position
+- [erase](erase.md) - remove an object member, an array element, or the value a JSON pointer refers to
+- [root](root.md) - the view of the root value
+- [`BasicJsonType::push_back`](../basic_json/push_back.md) - the corresponding function of `basic_json`
+- [Edits](index.md#edits) - what an edit guarantees, for every overload
+
+## Version history
+
+- Added in version 3.13.0.

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

@@ -80,6 +80,7 @@ compile; see [`parse`](parse.md#notes).
 
 - [parse](parse.md) - deserialize from a compatible input
 - [root](root.md) - the view of the root value
+- [load](load.md) - read a document from an image instead of parsing JSON text
 
 ## Version history
 

docs/mkdocs/docs/api/basic_json_document/save.md

@@ -0,0 +1,104 @@
+# <small>nlohmann::basic_json_document::</small>save
+
+```cpp
+std::vector<std::uint8_t> save() const;
+```
+
+Writes the document as an *image*: a byte buffer that [`load`](load.md) reads back without parsing. The image holds
+the node index, the source text (plus, for an edited document, the number tokens edits wrote), and the decoded
+strings (plus the strings edits wrote) -- everything [`root()`](root.md) needs, with nothing left to parse.
+
+An edited document is written in its *current* state, with its values in document order, the way the library's own
+parser would have produced them for that JSON text: a member [`set`](set.md) added goes at the end, an
+[`erase`](erase.md)d member leaves no trace, and a float that is not finite (NaN or positive/negative infinity)
+becomes null, the same substitution [`dump()`](../basic_json_view/dump.md) makes. The same document always saves to
+the same bytes -- also across `BasicJsonType` and `#!cpp Editable`, since the image reflects document order and
+values only, not which specialization produced them.
+
+## Return value
+
+The image, as a `#!cpp std::vector<std::uint8_t>`. Pass it, or a pointer to its data together with its size, to
+[`load`](load.md) to read the document back.
+
+## Exception safety
+
+Strong guarantee: `save()` does not modify `#!cpp *this` (it is `#!cpp const`), so if it throws, the document is left
+exactly as it was, and the partially built image is discarded with the exception.
+
+## Exceptions
+
+Throws [`type_error.320`](../../home/exceptions.md#jsonexceptiontype_error320) if the document is
+[discarded](is_discarded.md) -- a default-constructed document, or one a failed [`parse()`](parse.md)/
+[`read()`](read.md) with `allow_exceptions == false` left discarded.
+
+On a big-endian target, throws `type_error.320` with a different message instead: the image format is little-endian
+only (see [Notes](#notes)).
+
+Throws [`out_of_range.416`](../../home/exceptions.md#jsonexceptionout_of_range416) if the node count, the text, or
+the decoded strings of the image would individually reach 4 GiB -- the same 32-bit offsets
+[`parse()`](parse.md#exceptions) and, for edits, [`set`](set.md)/[`push_back`](push_back.md) are already limited to.
+
+!!! failure "Example messages"
+
+    ```
+    [json.exception.type_error.320] cannot save a discarded json_document
+    ```
+    ```
+    [json.exception.type_error.320] json_document images need a little-endian target
+    ```
+    ```
+    [json.exception.out_of_range.416] images of 4 GiB or more are not supported by json_document
+    ```
+
+## Complexity
+
+Linear in the size of the document: the number of nodes, plus the length of the text and the decoded strings that end
+up in the image.
+
+## Notes
+
+**Format.** The image begins with a 64-byte header (the magic bytes `#!cpp "NJVI"`, a version number, the node count,
+and the sizes of the text and the decoded strings, all little-endian), followed by the nodes
+([16 bytes each](../../home/architecture.md#node-index-of-json-views)), the text and a `#!cpp '\0'`, and the decoded
+strings and a `#!cpp '\0'`. [`load`](load.md) checks the header, and the sizes it describes, before reading anything
+else -- see [`load`'s Exceptions](load.md#exceptions).
+
+!!! warning "Experimental"
+
+    The image format is versioned but not yet stable: it may change in an incompatible way before it is declared
+    stable. Use images to cache a document within one build of the library, or to hand one to another process running
+    the *same* build on the *same* (little-endian) machine -- not as a long-term storage format. Keep the original
+    JSON text if you need to read a saved document back with a future library version.
+
+**Little-endian only.** The image is written as raw little-endian bytes, with no byte-swapping. `save()` (and
+[`load`](load.md)) throw `type_error.320` on a big-endian target rather than silently produce bytes a big-endian
+reader could not interpret correctly.
+
+## Examples
+
+??? example "Caching a parsed document as an image"
+
+    The example below saves a parsed configuration as an image -- the way a service might cache one to answer later
+    requests without parsing the text again -- and confirms that loading it back gives exactly the same result as
+    parsing did, and that saving is deterministic.
+
+    ```cpp
+    --8<-- "examples/basic_json_document__save.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/basic_json_document__save.output"
+    ```
+
+## See also
+
+- [load](load.md) - read an image written by `save()`
+- [owns_source](owns_source.md) - return whether the document holds its own copy of the text
+- [`basic_json_view::dump`](../basic_json_view/dump.md) - serialize the document to JSON text instead of an image
+- [Images](../../features/json_view.md#images) - why and when to use images
+
+## Version history
+
+- Added in version 3.13.0.

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

@@ -0,0 +1,203 @@
+# <small>nlohmann::basic_json_document::</small>set
+
+```cpp
+// (1)
+template<typename V>
+view_type set(view_type target, V&& value);
+
+// (2)
+template<typename V>
+view_type set(view_type object, string_view_t key, V&& value);
+
+// (3)
+template<typename I, typename V>
+view_type set(view_type array, I idx, V&& value);
+
+// (4)
+template<typename V>
+view_type set(const json_pointer& ptr, V&& value);
+```
+
+Only an **editable** document (`#!cpp Editable == true`, e.g. [`json_editable_document`](../json_editable_document.md))
+has `set`; calling it on a read-only `basic_json_document` fails to compile (`#!cpp static_assert`).
+
+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
+   [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 <
+   array.size()`).
+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. 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
+is copied so that nothing is shared with the source document afterward; a `BasicJsonType` value; or anything
+`BasicJsonType` can be constructed from (numbers, strings, `#!cpp bool`, `#!cpp nullptr`, containers, ...).
+
+## Template parameters
+
+`V`
+:   the type of `value`, deduced; see above for what is accepted.
+
+`I`
+:   an integral type other than `#!cpp bool`, deduced (overloads taking a `#!cpp bool` or a non-integral type for
+    `idx` do not participate in overload resolution).
+
+## Parameters
+
+`target` (in)
+:   the value to replace
+
+`object` (in)
+:   the object (or null value) whose member to set
+
+`array` (in)
+:   the array whose element to assign
+
+`key` (in)
+:   the key of the member to set
+
+`idx` (in)
+:   the index of the element to assign; a negative value throws (see [Exceptions](#exceptions))
+
+`ptr` (in)
+:   a JSON pointer to the value to set, relative to `root()`
+
+`value` (in)
+:   the new value
+
+## Return value
+
+1. a view of `target`, now holding `value`
+2. a view of the member `key` of `object`, now holding `value`
+3. a view of the element `idx` of `array`, now holding `value`
+4. a view of the value `ptr` refers to, now holding `value`
+
+## Exception safety
+
+Basic exception safety: `value` is fully encoded -- including the checks below -- into storage owned by the document
+before anything already reachable from [`root()`](root.md) is touched, so a failure while encoding `value` (an
+invalid argument, or `#!cpp std::bad_alloc`) leaves the document completely unchanged, other than memory allocated
+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. 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
+
+1. Throws [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) if `value` is a
+   [discarded](../basic_json_view/is_discarded.md) view, or a [discarded](../basic_json/is_discarded.md)
+   `BasicJsonType` value (e.g. `#!cpp BasicJsonType(value_t::discarded)`) -- an object or array `value`, of either
+   kind, is fine and is encoded as a whole subtree.
+2. Throws [`type_error.305`](../../home/exceptions.md#jsonexceptiontype_error305) if `object` is neither an object
+   nor null -- the same message [`operator[]`](../basic_json_view/operator%5B%5D.md) throws for a string argument on
+   such a value. Throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) if `key` is not
+   valid UTF-8, with the same message [`BasicJsonType::dump()`](../basic_json/dump.md) gives for that string.
+   Also throws what 1. throws for `value`.
+3. Throws `type_error.305` if `array` is not an array -- the same message `operator[]` throws for a numeric argument
+   on such a value. Throws [`out_of_range.401`](../../home/exceptions.md#jsonexceptionout_of_range401) if `idx` is
+   negative, or if `#!cpp idx >= array.size()`. Also throws what 1. throws for `value`.
+4. Throws what [`at`](../basic_json_view/at.md) throws (overload 3) for resolving `ptr`'s parent, except that a
+   missing object member or an array index equal to the array's size at the very last reference token is not an
+   error there (it becomes a new member or an appended element) instead of
+   [`out_of_range.403`](../../home/exceptions.md#jsonexceptionout_of_range403)/[`out_of_range.402`](../../home/exceptions.md#jsonexceptionout_of_range402).
+   For the last reference token itself: if the parent is an object (or a primitive value, where it throws
+   `type_error.305`), throws what 2. throws; if the parent is an array, throws what 3. throws for an index that is
+   out of range, or, for a token that is not a valid array index,
+   [`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); 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
+[`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202) ("view does not belong to this
+document") if `target`/`object`/`array` is a [discarded](../basic_json_view/is_discarded.md) view or a view of a
+*different* document (overloads 1-3 only; overload 4 always starts from this document's own [`root()`](root.md)).
+
+## Complexity
+
+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 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; 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[]`.
+
+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
+[`push_back`](push_back.md) or `set` on the same container reuses that block, growing it (amortized constant time)
+only once it runs out of room. This never moves an element itself -- only where the container's *links* to its
+elements live -- so a view of an element stays valid, but any iterator already taken over the container is
+invalidated, since it was walking the old layout. See [Edits](index.md#edits) for what stays valid across an edit in
+general.
+
+The same switch happens, for the same reason, when overload 1. replaces a multi-node array/object value with a
+scalar: the *parent's* element sequence is what has to switch to links, not `target` itself, because the parent
+originally stepped over `target`'s whole subtree by its node count, which no longer applies once `target` is a
+one-node scalar.
+
+## Examples
+
+??? example "Example: (1)/(2)/(3)/(4) replace a value, set a member, assign an element, set via a JSON pointer"
+
+    The example below edits a small configuration document -- replacing a value, adding an object member, assigning
+    an array element, and reaching a field through a JSON pointer -- and shows what
+    [`dump()`](../basic_json_view/dump.md) preserves that is lost once the same edits are made on a `BasicJsonType`
+    value instead: the order object members were written in, and the exact spelling of a number that was never
+    touched.
+
+    ```cpp
+    --8<-- "examples/basic_json_document__set.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/basic_json_document__set.output"
+    ```
+
+## See also
+
+- [push_back](push_back.md) - append to an array
+- [insert](insert.md) - insert an element into an array
+- [erase](erase.md) - remove an object member, an array element, or the value a JSON pointer refers to
+- [root](root.md) - the view of the root value, the starting point of overload 4
+- [`basic_json_view::dump`](../basic_json_view/dump.md) - serialize the document, keeping an untouched number's
+  spelling with `#!cpp number_format::source`
+- [Edits](index.md#edits) - what an edit guarantees, for every overload
+- [Editing a document](../../features/json_view.md#editing-a-document) - why editable documents keep the source
+  text's order and number spelling
+
+## Version history
+
+- Added in version 3.13.0.

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

@@ -3,7 +3,7 @@
 <small>Defined in header `<nlohmann/json_view.hpp>`</small>
 
 ```cpp
-template<typename BasicJsonType>
+template<typename BasicJsonType, bool Editable = false>
 class basic_json_view;
 ```
 
@@ -36,16 +36,30 @@ Moving the document itself does not invalidate its views: the index is heap-allo
 [`json_pointer`](../json_pointer/index.md). Unlike `basic_json`, there are no implicit conversion operators (no
 `#!cpp operator ValueType()`), and no `#!cpp get_ptr()` or `#!cpp get_ref()`; see [`get`](get.md).
 
+`basic_json_view` itself is always read-only -- it never has a `set` or `push_back` of its own. A view of an
+**editable** document (`#!cpp Editable == true`) sees every edit made through
+[`basic_json_document::set`](../basic_json_document/set.md) and
+[`basic_json_document::push_back`](../basic_json_document/push_back.md): once a value is changed, every view that
+still refers to it -- including ones taken before the change -- reads the new value. See
+[Edits](../basic_json_document/index.md#edits).
+
 ## Template parameters
 
 `BasicJsonType`
 :   a specialization of [`basic_json`](../basic_json/index.md), matching the
     [`basic_json_document`](../basic_json_document/index.md) the view was taken from.
 
+`Editable`
+:   whether the view is of an editable document, matching the [`basic_json_document`](../basic_json_document/index.md)
+    it was taken from (optional, `#!cpp false` by default). See [Edits](../basic_json_document/index.md#edits).
+
 ## Specializations
 
 - [**json_view**](../json_view.md) - views of a [`json_document`](../json_document.md)
 - [**ordered_json_view**](../ordered_json_view.md) - views of an [`ordered_json_document`](../ordered_json_document.md)
+- [**json_editable_view**](../json_editable_view.md) - views of a [`json_editable_document`](../json_editable_document.md)
+- [**ordered_json_editable_view**](../ordered_json_editable_view.md) - views of an
+  [`ordered_json_editable_document`](../ordered_json_editable_document.md)
 
 ## Member types
 

docs/mkdocs/docs/api/json_editable_document.md

@@ -0,0 +1,43 @@
+# <small>nlohmann::</small>json_editable_document
+
+<small>Defined in header `<nlohmann/json_view.hpp>`</small>
+
+```cpp
+using json_editable_document = basic_json_document<json, true>;
+```
+
+This type is an **editable** [`basic_json_document`](basic_json_document/index.md) of the default
+[`json`](json.md) specialization: in addition to everything [`json_document`](json_document.md) offers,
+[`set`](basic_json_document/set.md) and [`push_back`](basic_json_document/push_back.md) change values after
+parsing, without ever rewriting the source text -- see [Edits](basic_json_document/index.md#edits) and
+[Editing a document](../features/json_view.md#editing-a-document).
+
+## Examples
+
+??? example
+
+    The example below patches two fields of a small configuration document -- changing one and adding another --
+    and dumps it back out with the member order and the spelling of the untouched number preserved, something a
+    plain [`json`](json.md) value cannot do.
+
+    ```cpp
+    --8<-- "examples/json_editable_document.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/json_editable_document.output"
+    ```
+
+## See also
+
+- [json_editable_view](json_editable_view.md) - a view of a value of a `json_editable_document`
+- [json_document](json_document.md) - the read-only document this type adds edits to
+- [ordered_json_editable_document](ordered_json_editable_document.md) - the corresponding editable document for
+  `ordered_json`
+- [Edits](basic_json_document/index.md#edits) - what an edit guarantees
+
+## Version history
+
+Since version 3.13.0.

docs/mkdocs/docs/api/json_editable_view.md

@@ -0,0 +1,41 @@
+# <small>nlohmann::</small>json_editable_view
+
+<small>Defined in header `<nlohmann/json_view.hpp>`</small>
+
+```cpp
+using json_editable_view = basic_json_view<json, true>;
+```
+
+This type is a [`basic_json_view`](basic_json_view/index.md) of a value of a
+[`json_editable_document`](json_editable_document.md). It offers the same read-only interface as
+[`json_view`](json_view.md); what is different is what it can be a view *of* -- a value that
+[`set`](basic_json_document/set.md) and [`push_back`](basic_json_document/push_back.md) can change, with every view
+still referring to it seeing the change, see [Edits](basic_json_document/index.md#edits).
+
+## Examples
+
+??? example
+
+    The example below is the same as [`json_editable_document`'s](json_editable_document.md): every view read back
+    out of the document -- `#!cpp doc.root()` and the views nested under it -- sees the edits made through `set`.
+
+    ```cpp
+    --8<-- "examples/json_editable_document.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/json_editable_document.output"
+    ```
+
+## See also
+
+- [json_editable_document](json_editable_document.md) - the document type this view refers into
+- [json_view](json_view.md) - the corresponding read-only view
+- [ordered_json_editable_view](ordered_json_editable_view.md) - the corresponding view for
+  `ordered_json_editable_document`
+
+## Version history
+
+Since version 3.13.0.

docs/mkdocs/docs/api/ordered_json_editable_document.md

@@ -0,0 +1,47 @@
+# <small>nlohmann::</small>ordered_json_editable_document
+
+<small>Defined in header `<nlohmann/json_view.hpp>`</small>
+
+```cpp
+using ordered_json_editable_document = basic_json_document<ordered_json, true>;
+```
+
+This type is an **editable** [`basic_json_document`](basic_json_document/index.md) of the
+[`ordered_json`](ordered_json.md) specialization: [`set`](basic_json_document/set.md) and
+[`push_back`](basic_json_document/push_back.md) change values after parsing, as for
+[`json_editable_document`](json_editable_document.md), and
+[`materialize()`](basic_json_view/materialize.md) preserves the document order of object members -- including
+members [`set`](basic_json_document/set.md) added -- instead of sorting them like
+[`json_editable_document`](json_editable_document.md) does.
+
+## Examples
+
+??? example
+
+    The example below edits a document with `set`, then shows that `materialize()` keeps the member order of the
+    source text (with the new member at the end) for `ordered_json_editable_document`, where it would sort the
+    members alphabetically for [`json_editable_document`](json_editable_document.md).
+
+    ```cpp
+    --8<-- "examples/ordered_json_editable_document.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/ordered_json_editable_document.output"
+    ```
+
+## See also
+
+- [ordered_json_editable_view](ordered_json_editable_view.md) - a view of a value of an
+  `ordered_json_editable_document`
+- [ordered_json_document](ordered_json_document.md) - the read-only document this type adds edits to
+- [json_editable_document](json_editable_document.md) - the corresponding editable document for the default `json`
+  specialization
+- [Object Order](../features/object_order.md)
+- [Edits](basic_json_document/index.md#edits) - what an edit guarantees
+
+## Version history
+
+Since version 3.13.0.

docs/mkdocs/docs/api/ordered_json_editable_view.md

@@ -0,0 +1,40 @@
+# <small>nlohmann::</small>ordered_json_editable_view
+
+<small>Defined in header `<nlohmann/json_view.hpp>`</small>
+
+```cpp
+using ordered_json_editable_view = basic_json_view<ordered_json, true>;
+```
+
+This type is a [`basic_json_view`](basic_json_view/index.md) of a value of an
+[`ordered_json_editable_document`](ordered_json_editable_document.md), the corresponding view for
+[`ordered_json_view`](ordered_json_view.md) the way [`json_editable_view`](json_editable_view.md) is for
+[`json_view`](json_view.md).
+
+## Examples
+
+??? example
+
+    The example below is the same as [`ordered_json_editable_document`'s](ordered_json_editable_document.md): the
+    views `set` returns see the document's member order preserved on `materialize()`, unlike for a
+    [`json_editable_document`](json_editable_document.md).
+
+    ```cpp
+    --8<-- "examples/ordered_json_editable_document.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/ordered_json_editable_document.output"
+    ```
+
+## See also
+
+- [ordered_json_editable_document](ordered_json_editable_document.md) - the document type this view refers into
+- [ordered_json_view](ordered_json_view.md) - the corresponding read-only view
+- [json_editable_view](json_editable_view.md) - the corresponding view for `json_editable_document`
+
+## Version history
+
+Since version 3.13.0.

docs/mkdocs/docs/examples/basic_json_document__erase.cpp

@@ -0,0 +1,38 @@
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using json = nlohmann::json;
+using json_editable_document = nlohmann::json_editable_document;
+using json_editable_view = nlohmann::json_editable_view;
+
+int main()
+{
+    // a deprecated field is dropped from a configuration file, and a
+    // decommissioned replica is removed from the list -- "price" keeps its
+    // trailing zero, and the fields around the removed ones keep their order
+    const std::string text = R"({
+  "name": "cache",
+  "legacy_host": "db0",
+  "host": "db1",
+  "price": 19.90,
+  "replicas": ["db2", "db3", "db4"]
+})";
+
+    json_editable_document doc = json_editable_document::parse(text);
+
+    doc.erase(doc.root(), "legacy_host");                                      // (1) an object member
+    doc.erase(doc.root()["replicas"], 1);                                      // (2) an array element ("db3")
+    const std::size_t removed = doc.erase(json::json_pointer("/replicas/0"));  // (3) via a JSON pointer
+
+    std::cout << removed << '\n';
+    std::cout << doc.root().dump(2, ' ', false, json_editable_view::number_format::source) << "\n\n";
+
+    // the same edits on a plain json value: object_t is a std::map, so
+    // parsing already sorted the keys, and dump() rewrites every number to
+    // its shortest form, even "price", which was never touched
+    json plain = json::parse(text);
+    plain.erase("legacy_host");
+    plain["replicas"].erase(1);
+    plain["replicas"].erase(0);
+    std::cout << plain.dump(2) << '\n';
+}

docs/mkdocs/docs/examples/basic_json_document__erase.output

@@ -0,0 +1,18 @@
+1
+{
+  "name": "cache",
+  "host": "db1",
+  "price": 19.90,
+  "replicas": [
+    "db4"
+  ]
+}
+
+{
+  "host": "db1",
+  "name": "cache",
+  "price": 19.9,
+  "replicas": [
+    "db4"
+  ]
+}

docs/mkdocs/docs/examples/basic_json_document__insert.cpp

@@ -0,0 +1,38 @@
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using json = nlohmann::json;
+using json_editable_document = nlohmann::json_editable_document;
+using json_editable_view = nlohmann::json_editable_view;
+
+int main()
+{
+    // a deployment plan -- "budget" is written with a trailing zero that has
+    // no effect on its value
+    const std::string text = R"({
+  "release": "2026.09",
+  "steps": ["build", "test", "deploy"],
+  "budget": 19.90
+})";
+
+    json_editable_document doc = json_editable_document::parse(text);
+
+    const std::size_t deploy_index = 2;
+    const auto deploy = doc.root()["steps"][deploy_index];  // held across the insert
+
+    doc.insert(doc.root()["steps"], deploy_index, "smoke-test"); // insert before "deploy"
+
+    // the held view still refers to "deploy", even though its index moved
+    // from 2 to 3, and nothing else in the document was touched
+    std::cout << deploy.dump() << '\n';
+    std::cout << doc.root().dump(2, ' ', false, json_editable_view::number_format::source) << "\n\n";
+
+    // the same edit on a plain json value: an index held from before the
+    // insert now refers to whatever moved into that slot, and dump()
+    // rewrites "budget" to its shortest form even though it was never
+    // touched
+    json plain = json::parse(text);
+    plain["steps"].insert(plain["steps"].begin() + static_cast<std::ptrdiff_t>(deploy_index), "smoke-test");
+    std::cout << plain["steps"][deploy_index].dump() << '\n';
+    std::cout << plain.dump(2) << '\n';
+}

docs/mkdocs/docs/examples/basic_json_document__insert.output

@@ -0,0 +1,23 @@
+"deploy"
+{
+  "release": "2026.09",
+  "steps": [
+    "build",
+    "test",
+    "smoke-test",
+    "deploy"
+  ],
+  "budget": 19.90
+}
+
+"smoke-test"
+{
+  "budget": 19.9,
+  "release": "2026.09",
+  "steps": [
+    "build",
+    "test",
+    "smoke-test",
+    "deploy"
+  ]
+}

docs/mkdocs/docs/examples/basic_json_document__load.cpp

@@ -0,0 +1,52 @@
+#include <cstdint>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <nlohmann/json_view.hpp>
+
+using json = nlohmann::json;
+using json_document = nlohmann::json_document;
+using image_check = json_document::image_check;
+
+int main()
+{
+    std::cout << std::boolalpha;
+
+    // the image of a parsed document -- as if read back from a cache file or
+    // received from another process running the same build of the library
+    const std::string text = R"({"name": "cache", "note": "caf\u00e9", "replicas": ["db2", "db3"]})";
+    const json_document parsed = json_document::parse(text);
+    const std::vector<std::uint8_t> image = parsed.save();
+
+    // (1)/(2) load() needs no parsing, yet dumps exactly what parsing did
+    const json_document borrowed = json_document::load(image);
+    std::cout << (borrowed.root().dump() == parsed.root().dump()) << '\n';
+    std::cout << borrowed.owns_source() << '\n'; // borrowed: still points into `image`
+
+    // (3) load(std::move(image)) keeps the vector instead of copying it
+    std::vector<std::uint8_t> to_move = image;
+    const json_document owned = json_document::load(std::move(to_move));
+    std::cout << owned.owns_source() << '\n';
+
+    // a damaged image -- the last byte of the decoded string "note" holds
+    // (an escape sequence, so it was unescaped into the document's own
+    // buffer), flipped, as storage or transport corruption might do
+    std::vector<std::uint8_t> damaged = image;
+    damaged[damaged.size() - 2] = 0xFF;
+
+    // image_check::full inspects strings and numbers, so it catches the damage
+    try
+    {
+        static_cast<void>(json_document::load(damaged, image_check::full));
+    }
+    catch (const json::parse_error& e)
+    {
+        std::cout << e.id << '\n';
+    }
+
+    // image_check::bounds only checks structure and bounds, so a cache the
+    // process already trusts loads without the extra scan -- reading a value
+    // the damage did not touch is still safe
+    const json_document trusted = json_document::load(damaged, image_check::bounds);
+    std::cout << trusted.root()["name"].get<std::string>() << '\n';
+}

docs/mkdocs/docs/examples/basic_json_document__load.output

@@ -0,0 +1,5 @@
+true
+false
+true
+116
+cache

docs/mkdocs/docs/examples/basic_json_document__push_back.cpp

@@ -0,0 +1,24 @@
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using json = nlohmann::json;
+using json_editable_document = nlohmann::json_editable_document;
+
+int main()
+{
+    // "events" starts out null -- the first push_back() turns it into an
+    // array, exactly like set() turns a null object member into an object
+    json_editable_document doc = json_editable_document::parse(R"({"source": "sensor-1", "events": null})");
+
+    const auto first = doc.push_back(doc.root()["events"], json{{"type", "start"}, {"t", 0}});
+    for (int t = 1; t <= 3; ++t)
+    {
+        doc.push_back(doc.root()["events"], json{{"type", "tick"}, {"t", t}});
+    }
+
+    // push_back() never moves an existing element: a view taken from an
+    // earlier call still refers to the same element after later ones
+    std::cout << first.dump() << '\n';
+    std::cout << doc.root()["events"].size() << '\n';
+    std::cout << doc.root().dump(2) << '\n';
+}

docs/mkdocs/docs/examples/basic_json_document__push_back.output

@@ -0,0 +1,23 @@
+{"t":0,"type":"start"}
+4
+{
+  "source": "sensor-1",
+  "events": [
+    {
+      "t": 0,
+      "type": "start"
+    },
+    {
+      "t": 1,
+      "type": "tick"
+    },
+    {
+      "t": 2,
+      "type": "tick"
+    },
+    {
+      "t": 3,
+      "type": "tick"
+    }
+  ]
+}

docs/mkdocs/docs/examples/basic_json_document__save.cpp

@@ -0,0 +1,30 @@
+#include <cstdint>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <nlohmann/json_view.hpp>
+
+using json_document = nlohmann::json_document;
+
+int main()
+{
+    std::cout << std::boolalpha;
+
+    // a configuration a service parses once and then caches as an image, so
+    // that later requests can load() it instead of parsing the text again
+    const std::string text = R"({"name": "cache", "host": "db1", "port": 6379, "replicas": ["db2", "db3"]})";
+    const json_document config = json_document::parse(text);
+
+    // save() turns the parsed document into a byte buffer: a 64-byte header,
+    // the node index, the source text, and the decoded strings
+    const std::vector<std::uint8_t> image = config.save();
+    std::cout << image.size() << '\n';
+
+    // the same document always saves to the same bytes
+    std::cout << (image == json_document::parse(text).save()) << '\n';
+
+    // loading the image back needs no parsing, yet dumps exactly what
+    // parsing the text produced
+    const json_document reloaded = json_document::load(image);
+    std::cout << (reloaded.root().dump() == config.root().dump()) << '\n';
+}

docs/mkdocs/docs/examples/basic_json_document__save.output

@@ -0,0 +1,3 @@
+316
+true
+true

docs/mkdocs/docs/examples/basic_json_document__set.cpp

@@ -0,0 +1,41 @@
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using json = nlohmann::json;
+using json_editable_document = nlohmann::json_editable_document;
+using json_editable_view = nlohmann::json_editable_view;
+
+int main()
+{
+    // a configuration file, as it might be read from disk -- "price" is
+    // written with a trailing zero that has no effect on its value
+    const std::string text = R"({
+  "name": "cache",
+  "host": "db1",
+  "port": 6379,
+  "price": 19.90,
+  "replicas": ["db2", "db3"],
+  "timeout": 30
+})";
+
+    json_editable_document doc = json_editable_document::parse(text);
+
+    doc.set(doc.root()["port"], 6380);                    // (1) replace a value
+    doc.set(doc.root(), "region", "us-east");              // (2) add a member
+    doc.set(doc.root()["replicas"], 0, "db4");             // (3) assign an element
+    doc.set(json::json_pointer("/timeout"), 45);           // (4) via a JSON pointer
+
+    // members stay in document order (the new one at the end), and a number
+    // that was not itself edited keeps its exact spelling
+    std::cout << doc.root().dump(2, ' ', false, json_editable_view::number_format::source) << "\n\n";
+
+    // the same edits on a plain json value: object_t is a std::map, so
+    // parsing already sorted the keys, and dump() rewrites every number to
+    // its shortest form, even "price", which was never touched
+    json plain = json::parse(text);
+    plain["port"] = 6380;
+    plain["region"] = "us-east";
+    plain["replicas"][0] = "db4";
+    plain[json::json_pointer("/timeout")] = 45;
+    std::cout << plain.dump(2) << '\n';
+}

docs/mkdocs/docs/examples/basic_json_document__set.output

@@ -0,0 +1,25 @@
+{
+  "name": "cache",
+  "host": "db1",
+  "port": 6380,
+  "price": 19.90,
+  "replicas": [
+    "db4",
+    "db3"
+  ],
+  "timeout": 45,
+  "region": "us-east"
+}
+
+{
+  "host": "db1",
+  "name": "cache",
+  "port": 6380,
+  "price": 19.9,
+  "region": "us-east",
+  "replicas": [
+    "db4",
+    "db3"
+  ],
+  "timeout": 45
+}

docs/mkdocs/docs/examples/json_editable_document.cpp

@@ -0,0 +1,30 @@
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using json = nlohmann::json;
+using json_editable_document = nlohmann::json_editable_document;
+using json_editable_view = nlohmann::json_editable_view;
+
+int main()
+{
+    // a configuration file, as it might be read from disk
+    const std::string text = R"({"name": "cache", "host": "db1", "port": 6379, "price": 19.90})";
+    std::cout << text << "\n\n";
+
+    // patch two fields -- "price" is never touched
+    json_editable_document doc = json_editable_document::parse(text);
+    doc.set(doc.root(), "host", "db2");
+    doc.set(doc.root(), "retries", 3);
+
+    // member order (the new member at the end) and the untouched number's
+    // exact spelling survive
+    std::cout << doc.root().dump(-1, ' ', false, json_editable_view::number_format::source) << '\n';
+
+    // the same patch on a plain json value: keys are sorted (object_t is a
+    // std::map), and "price" is rewritten even though the patch never
+    // touched it
+    json plain = json::parse(text);
+    plain["host"] = "db2";
+    plain["retries"] = 3;
+    std::cout << plain.dump() << '\n';
+}

docs/mkdocs/docs/examples/json_editable_document.output

@@ -0,0 +1,4 @@
+{"name": "cache", "host": "db1", "port": 6379, "price": 19.90}
+
+{"name":"cache","host":"db2","port":6379,"price":19.90,"retries":3}
+{"host":"db2","name":"cache","port":6379,"price":19.9,"retries":3}

docs/mkdocs/docs/examples/ordered_json_editable_document.cpp

@@ -0,0 +1,15 @@
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using ordered_json_editable_document = nlohmann::ordered_json_editable_document;
+
+int main()
+{
+    // ordered_json_editable_document is basic_json_document<nlohmann::ordered_json, true>
+    ordered_json_editable_document doc = ordered_json_editable_document::parse(R"({"z": 1, "a": 2, "m": 3})");
+    doc.set(doc.root(), "b", 4); // set() always appends a new member at the end
+
+    // materialize() preserves the document order (with "b" at the end),
+    // instead of sorting the keys the way json_editable_document does
+    std::cout << doc.root().materialize().dump() << '\n';
+}

docs/mkdocs/docs/examples/ordered_json_editable_document.output

@@ -0,0 +1 @@
+{"z":1,"a":2,"m":3,"b":4}

docs/mkdocs/docs/features/index.md

@@ -14,6 +14,8 @@ C++ types, and finally serialize it again.
   [parsing untrusted input](parsing/untrusted_input.md).
 - [Zero-copy JSON views](json_view.md) — read a JSON text through a flat index instead of building a `json` tree;
   strings and numbers stay in the input and are only decoded when needed.
+  [Editable documents](json_view.md#editing-a-document) can also be modified, and [images](json_view.md#images) load a
+  parsed document again without parsing it.
 - [Comments](comments.md) and [trailing commas](trailing_commas.md) — opt-in relaxations of the JSON grammar.
 
 ## Accessing and modifying values

docs/mkdocs/docs/features/json_view.md

@@ -249,14 +249,129 @@ a number to its parsed `#!cpp double`/`#!cpp int64_t` value.
 [`operator<<`](../api/basic_json_view/operator_ltlt.md) writes a view to a stream the way `basic_json`'s does, using
 the stream's `width`/`fill` for indentation.
 
+## Editing a document
+
+Everything above is read-only: a `json_document`/`json_view` lets you look at a parsed text without copying it, but
+not change it. [`basic_json_document<BasicJsonType, true>`](../api/basic_json_document/index.md) -- more conveniently
+spelled [`json_editable_document`](../api/json_editable_document.md) or
+[`ordered_json_editable_document`](../api/ordered_json_editable_document.md) -- also lets you
+[`set`](../api/basic_json_document/set.md) a value, [`push_back`](../api/basic_json_document/push_back.md) onto or
+[`insert`](../api/basic_json_document/insert.md) into an array, and [`erase`](../api/basic_json_document/erase.md)
+an object member or an array element, still without ever building a `basic_json` tree for parts you do not touch.
+
+`#!cpp Editable` defaults to `#!cpp false`, so `json_document`/`ordered_json_document` are unaffected -- they carry
+none of the bookkeeping edits need, and calling `set`/`push_back`/`insert`/`erase` on one is a compile error, not a
+runtime one.
+
+### Why: editing without reformatting
+
+The `#!cpp 19.90` price from [above](#writing-a-view-back) is exactly the kind of value that makes editing a `json`
+or `ordered_json` value in place lossy. Say you parse a configuration file, patch one field, and write it back:
+
+- **`json`** re-sorts every key on the way in (`object_t` is a `#!cpp std::map`) and rewrites every number to its
+  shortest round-trip form on the way out -- a one-field patch turns into a diff that reorders the whole file and
+  rewrites `#!cpp 19.90` to `#!cpp 19.9`.
+- **`ordered_json`** keeps the key order, but still rewrites every number the same way: parsing has already reduced
+  it to a `#!cpp double`/`#!cpp int64_t`, and there is no way back to how it was spelled in the source text.
+
+An editable document keeps both. [`dump()`](../api/basic_json_view/dump.md) of an edited document writes members in
+document order -- a member [`set`](../api/basic_json_document/set.md) added goes at the end, exactly where it was
+inserted, and an [`erase`](../api/basic_json_document/erase.md)d member simply leaves a gap: everything around it
+keeps its place -- and [`number_format::source`](../api/basic_json_view/number_format.md) keeps the exact spelling
+of every number an edit did not itself touch; a number an edit *did* touch is written the way
+[`BasicJsonType::dump()`](../api/basic_json/dump.md) would write it, since there is no source spelling for a brand
+new value.
+
+??? example "Example: patch a configuration, keeping member order and number spellings"
+
+    ```cpp
+    --8<-- "examples/json_editable_document.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/json_editable_document.output"
+    ```
+
+### What stays valid, and what an edit costs
+
+The source text itself is **never written**, and the parsed index never moves -- a value keeps the node it was
+parsed into for as long as it is not itself replaced. So every [view](../api/basic_json_view/index.md) taken before
+an edit, including a previously obtained [`root()`](../api/basic_json_document/root.md), stays valid and, if it
+still refers to the edited value, sees the edit; a view of a value a later edit drops or replaces just keeps showing
+what it last held. New values go to storage the document allocates and owns on demand. The one thing an edit does
+invalidate is the **iterators** taken over an edited array or object: the first time one of its elements is set,
+appended to, inserted into, or erased, its elements move from the parsed, fixed layout to a growable block of links
+so that [`push_back`](../api/basic_json_document/push_back.md) can later grow it in amortized constant time --
+existing elements are not touched, but an iterator that was walking the old layout no longer matches. A string
+obtained with
+[`get_string()`](../api/basic_json_view/get_string.md) is unaffected either way and stays valid across further
+edits. See [`basic_json_document`'s Edits](../api/basic_json_document/index.md#edits) for the details, and
+[`set`'s Exception safety](../api/basic_json_document/set.md#exception-safety) for what an edit guarantees if it
+throws (the *basic* guarantee, not the strong one `dump()` and the read-only functions provide). How edits are kept in
+the index is described in the [architecture overview](../home/architecture.md#node-index-of-json-views).
+
+## Images
+
+[`save()`](../api/basic_json_document/save.md) writes a document as an *image*: a byte buffer that
+[`load()`](../api/basic_json_document/load.md) reads back into a document without parsing -- no lexing, no building
+the node index, nothing but copying the nodes and pointing the text and the decoded strings at the image. Where
+[`parse_copy()`](../api/basic_json_document/parse_copy.md) still has to scan the whole input,
+[`load()`](../api/basic_json_document/load.md) turns that scan into a copy of the node index alone.
+
+**Why.** A document that is parsed once and then read many times -- a configuration loaded at startup, a template
+rendered on every request, a large reference dataset a worker process needs in memory -- pays for parsing once but
+can amortize [`save()`](../api/basic_json_document/save.md)'s cost across every later load. That makes images useful
+for a cache: save a document the first time it is parsed (to a file, a shared-memory segment, an in-process cache),
+and [`load()`](../api/basic_json_document/load.md) it on every later use instead of parsing the source text again.
+They are just as useful for handing a parsed document to another process (or a forked worker) running the same build
+of the library, since [`load()`](../api/basic_json_document/load.md) turns the transfer into a copy of the node index
+plus pointers into the received bytes, not a re-parse.
+
+**Choosing a check.** [`load()`](../api/basic_json_document/load.md) takes an
+[`image_check`](../api/basic_json_document/load.md#image_check) that trades validation against speed:
+`image_check::full` (the default) checks everything the parser itself guarantees, so a checked image is exactly as
+safe to read and serialize as a freshly parsed document -- the right choice whenever the image did not come straight
+from this process's own [`save()`](../api/basic_json_document/save.md), such as a file or a network peer.
+`image_check::bounds` only checks structure and bounds -- cheaper, since it skips scanning the text and the decoded
+strings -- and fits a cache the process trusts, one it wrote and reads back itself. `image_check::none` skips
+validation entirely, for an image trusted as much as the process's own memory. See
+[`load()`'s Notes](../api/basic_json_document/load.md#notes) for exactly what each level does and does not guarantee.
+
+??? example "Example: cache a parsed configuration as an image"
+
+    ```cpp
+    --8<-- "examples/basic_json_document__save.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/basic_json_document__save.output"
+    ```
+
+!!! warning "Experimental"
+
+    The image format is versioned but not yet stable, and may change in an incompatible way before it is declared
+    stable. It is little-endian only, and tied to the library build that wrote it -- use it to cache a document or to
+    hand one to another process running the *same* build, not as a long-term storage format; keep the original JSON
+    text if a saved document needs to be readable by a future library version.
+
+The idea of a document you can read without parsing comes from zero-copy formats such as
+[FlatBuffers](https://github.com/google/flatbuffers) and [YaFF](https://github.com/yandex/yaff); the check
+[`load()`](../api/basic_json_document/load.md) runs follows the idea of FlatBuffers' Verifier. No code is taken from
+either.
+
 ## Choosing between `json`, `ordered_json`, the SAX interface, and `json_view`
 
-| | [`json`](../api/json.md) / [`ordered_json`](../api/ordered_json.md) | [SAX interface](parsing/sax_interface.md) | [`json_document`](../api/json_document.md) / [`json_view`](../api/json_view.md) |
-|---|---|---|---|
-| **Ownership** | owns every value | owns nothing; you decide what to keep, in your handler | borrows or owns the *text*; the index is always owned by the document |
-| **Mutability** | freely mutable | not applicable (a one-shot event stream) | read-only |
-| **What you get** | a full tree you can read, write, and keep as long as you like | a sequence of callbacks; whatever your handler builds from them | a flat index plus, on demand, [`materialize()`](../api/basic_json_view/materialize.md)d `json`/`ordered_json` values for the parts you actually use |
-| **Typical use** | general-purpose JSON handling: config, request/response bodies you build or modify, anything you hold onto | validating or projecting a text into your own data structure without ever holding the whole thing as JSON | large or high-volume input where you only need part of it, or need it repeatedly, and can keep the source text (or a copy) alive for as long as the document lives |
+| | [`json`](../api/json.md) / [`ordered_json`](../api/ordered_json.md) | [SAX interface](parsing/sax_interface.md) | [`json_document`](../api/json_document.md) / [`json_view`](../api/json_view.md) | [`json_editable_document`](../api/json_editable_document.md) / [`json_editable_view`](../api/json_editable_view.md) |
+|---|---|---|---|---|
+| **Ownership** | owns every value | owns nothing; you decide what to keep, in your handler | borrows or owns the *text*; the index is always owned by the document | same as `json_document`; edits go to storage the document owns |
+| **Mutability** | freely mutable | not applicable (a one-shot event stream) | read-only | [`set`](../api/basic_json_document/set.md)/[`push_back`](../api/basic_json_document/push_back.md)/[`insert`](../api/basic_json_document/insert.md)/[`erase`](../api/basic_json_document/erase.md) edit in place; the source text is never rewritten |
+| **What you get** | a full tree you can read, write, and keep as long as you like | a sequence of callbacks; whatever your handler builds from them | a flat index plus, on demand, [`materialize()`](../api/basic_json_view/materialize.md)d `json`/`ordered_json` values for the parts you actually use | the same, plus [`dump()`](../api/basic_json_view/dump.md) of an edited document that keeps the member order and, with [`number_format::source`](../api/basic_json_view/number_format.md), the spelling of every untouched number |
+| **Typical use** | general-purpose JSON handling: config, request/response bodies you build or modify, anything you hold onto | validating or projecting a text into your own data structure without ever holding the whole thing as JSON | large or high-volume input where you only need part of it, or need it repeatedly, and can keep the source text (or a copy) alive for as long as the document lives | a document you read, patch a few fields of, and write back -- a configuration file, for instance -- where the rest of it should come back exactly as it was |
+| **Caching/reload** | not applicable -- re-parse, or roll your own serialization | not applicable | [`save()`](../api/basic_json_document/save.md)/[`load()`](../api/basic_json_document/load.md): cache the parsed index as an image and reload it without parsing | same, saving the document's current -- possibly edited -- state |
 
 ## Version history
 

docs/mkdocs/docs/home/architecture.md

@@ -194,8 +194,8 @@ packet-beta
 
 | Bytes | Field   | Type       | Contents                                                                                                                      |
 |-------|---------|------------|-------------------------------------------------------------------------------------------------------------------------------|
-| 0     | `kind`  | `uint8_t`  | the type, numbered as [`value_t`](../api/basic_json/value_t.md): 0 null, 1 object, 2 array, 3 string, 4 boolean, 5 signed integer, 6 unsigned integer, 7 float |
-| 1     | `flags` | `uint8_t`  | bits 0-1: where a string's bytes are (0: the source text, 1: the buffer of decoded strings, for strings with escapes); bit 2: the value of a boolean |
+| 0     | `kind`  | `uint8_t`  | the type, numbered as [`value_t`](../api/basic_json/value_t.md): 0 null, 1 object, 2 array, 3 string, 4 boolean, 5 signed integer, 6 unsigned integer, 7 float; 10 for a link (see below) |
+| 1     | `flags` | `uint8_t`  | bits 0-1: where a string's bytes (or a number's token) are (0: the source text, 1: the buffer of decoded strings, for strings with escapes, 2: the edit buffer); bit 2: the value of a boolean; bits 3 and 4: moved and new (see below) |
 | 2-3   | `extra` | `uint16_t` | numbers: the number of integer digits (low byte) and fraction digits (high byte), 255 for more; objects: the number of their key hash index (1-based), or 0; otherwise 0 |
 | 4-7   | `off`   | `uint32_t` | where the value starts: the first byte after a string's opening quote (or its position in the buffer of decoded strings), the first byte of a number or literal, the bracket of an array or object |
 | 8-11  | `len`   | `uint32_t` | strings: the length after decoding; floats and literals: the length of the token; arrays and objects: the number of elements |
@@ -245,6 +245,29 @@ flowchart LR
 All `flags` are 0. The integer's bytes 8-15 hold its value, 1; its `extra` says it has one digit. The float's `extra`
 says it has one integer and one fraction digit, and its `len` is that of the token `2.5`.
 
+Editable documents ([`json_editable_document`](../api/json_editable_document.md),
+[`detail/view/edit.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/view/edit.hpp) and
+[`detail/view/edit_storage.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/view/edit_storage.hpp))
+never write the source text and never move or resize the parsed index, so views stay valid while the document is
+edited:
+
+- A new scalar is written over its node. Its text (a string, or the token of a number as `dump()` writes it) goes to
+  the edit buffer, which `flags` bits 0-1 then name.
+- An array or object whose elements change gets the flag *moved* (bit 3): its elements then live in a separate
+  sequence (a header node, then the entries), whose number is in `off`. The entries are links (`kind` 10), whose bytes
+  8-15 hold the address of the value's node, so values never move.
+- A node written by an edit gets the flag *new* (bit 4): it has no position in the source text.
+- Views of read-only documents compile without any of this: how views walk the index is a template parameter
+  (`navigation<Editable>`).
+
+Images ([`save`](../api/basic_json_document/save.md) and [`load`](../api/basic_json_document/load.md),
+[`detail/view/image.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/view/image.hpp)) store
+the nodes as they are: a 64-byte header (the magic bytes `NJVI`, a format version, the sizes, and reserved bytes that
+must be zero), the nodes, the text, and the decoded strings. An edited document is first written in document order, as
+the parser would have written it (without links), and the numbers of the hash indexes are cleared, since `load`
+rebuilds the indexes. So a change of the node layout is a change of the image format: it must raise `image_version`,
+and `load` then rejects images of other versions (`parse_error.116`) instead of misreading them.
+
 ## Input adapters
 
 Input is read via **input adapters** that abstract a source. Every input adapter provides this interface:

docs/mkdocs/docs/home/exceptions.md

@@ -395,6 +395,23 @@ A UBJSON high-precision number could not be parsed.
     [json.exception.parse_error.115] parse error at byte 5: syntax error while parsing UBJSON high-precision number: invalid number text: 1A
     ```
 
+### json.exception.parse_error.116
+
+[`basic_json_document::load()`](../api/basic_json_document/load.md) rejected an
+[image](../features/json_view.md#images): either the bytes are not one [`save()`](../api/basic_json_document/save.md)
+could have written (too short, an unknown magic number or format version, or sizes that do not fit the buffer), or
+they are, but fail the requested [`image_check`](../api/basic_json_document/load.md#image_check).
+
+!!! failure "Example message"
+
+    ```
+    [json.exception.parse_error.116] parse error: invalid json_document image: the check failed
+    ```
+
+!!! note
+
+    This exception was added in version 3.13.0, together with [images](../features/json_view.md#images).
+
 ## Iterator errors
 
 This exception is thrown if iterators passed to a library function do not match
@@ -812,6 +829,45 @@ does not list an enumerator and it is therefore converted like the first listed
     [json.exception.type_error.318] duplicate object key 'red'
     ```
 
+### json.exception.type_error.319
+
+[`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.
+
+!!! failure "Example message"
+
+    ```
+    [json.exception.type_error.319] cannot store a binary value in a json_document
+    ```
+
+!!! note
+
+    This exception was added in version 3.13.0, together with editable [`json_document`s](../features/json_view.md).
+
+### json.exception.type_error.320
+
+[`basic_json_document::save()`](../api/basic_json_document/save.md) cannot write an
+[image](../features/json_view.md#images) of a [discarded](../api/basic_json_document/is_discarded.md) document.
+[`save()`](../api/basic_json_document/save.md) and [`load()`](../api/basic_json_document/load.md) also throw this
+exception on a big-endian target, since the image format is little-endian only.
+
+!!! failure "Example messages"
+
+    ```
+    [json.exception.type_error.320] cannot save a discarded json_document
+    ```
+    ```
+    [json.exception.type_error.320] json_document images need a little-endian target
+    ```
+
+!!! note
+
+    This exception was added in version 3.13.0, together with [images](../features/json_view.md#images).
+
 ### json.exception.type_error.321
 
 A discarded value (one created by [`parse()`](../api/basic_json/parse.md) with a callback that returns `false` for the
@@ -1066,13 +1122,24 @@ 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 4294967280 bytes (4 GiB minus 16 bytes) or more.
+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
+[image](../features/json_view.md#images): [`save()`](../api/basic_json_document/save.md) throws it if the node
+count, the text, or the decoded strings it would write would individually reach 4 GiB.
 
-!!! failure "Example message"
+!!! failure "Example messages"
 
     ```
     [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
+    ```
+    ```
+    [json.exception.out_of_range.416] images of 4 GiB or more are not supported by json_document
+    ```
 
 !!! note
 

docs/mkdocs/mkdocs.yml

@@ -239,14 +239,20 @@ nav:
           - 'Overview': api/basic_json_document/index.md
           - '(Constructor)': api/basic_json_document/basic_json_document.md
           - 'accept': api/basic_json_document/accept.md
+          - 'erase': api/basic_json_document/erase.md
+          - 'insert': api/basic_json_document/insert.md
           - 'is_discarded': api/basic_json_document/is_discarded.md
+          - 'load': api/basic_json_document/load.md
           - 'memory_usage': api/basic_json_document/memory_usage.md
           - 'node_count': api/basic_json_document/node_count.md
           - 'owns_source': api/basic_json_document/owns_source.md
           - 'parse': api/basic_json_document/parse.md
           - 'parse_copy': api/basic_json_document/parse_copy.md
+          - 'push_back': api/basic_json_document/push_back.md
           - 'read': api/basic_json_document/read.md
           - 'root': api/basic_json_document/root.md
+          - 'save': api/basic_json_document/save.md
+          - 'set': api/basic_json_document/set.md
           - 'shrink_to_fit': api/basic_json_document/shrink_to_fit.md
           - 'source': api/basic_json_document/source.md
       - basic_json_view:
@@ -308,6 +314,8 @@ nav:
           - 'to_json': api/adl_serializer/to_json.md
       - 'json': api/json.md
       - 'json_document': api/json_document.md
+      - 'json_editable_document': api/json_editable_document.md
+      - 'json_editable_view': api/json_editable_view.md
       - json_pointer:
           - 'Overview': api/json_pointer/index.md
           - '(Constructor)': api/json_pointer/json_pointer.md
@@ -349,6 +357,8 @@ nav:
       - 'operator""_json_pointer': api/operator_literal_json_pointer.md
       - 'ordered_json': api/ordered_json.md
       - 'ordered_json_document': api/ordered_json_document.md
+      - 'ordered_json_editable_document': api/ordered_json_editable_document.md
+      - 'ordered_json_editable_view': api/ordered_json_editable_view.md
       - 'ordered_json_view': api/ordered_json_view.md
       - 'ordered_map': api/ordered_map.md
       - macros:

include/nlohmann/detail/conversions/to_chars.hpp

@@ -1342,6 +1342,48 @@ inline char* write_shortest(char* first, const zmij::shortest_decimal d) noexcep
     return end + (three ? 5 : 4);
 }
 
+/// the powers of ten up to 10^16
+inline const std::array<std::uint64_t, 17>& powers_of_ten_16() noexcept
+{
+    static const std::array<std::uint64_t, 17> powers =
+    {
+        {
+            1u, 10u, 100u, 1000u, 10000u, 100000u, 1000000u, 10000000u, 100000000u, 1000000000u, 10000000000u,
+            100000000000u, 1000000000000u, 10000000000000u, 100000000000000u, 1000000000000000u, 10000000000000000u
+        }
+    };
+    return powers;
+}
+
+/*!
+@brief digits * 10^exp, as write_decimal() writes it, for the digits of a
+double that need no conversion (count digits, at most 15, the first not 0;
+trailing zeros allowed): extended to 16 digits and written by write_shortest()
+
+@return a pointer past the text; up to 41 bytes at @a first are written
+        (some beyond the returned end)
+*/
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_short_decimal(char* first, std::uint64_t digits, int count, int exp) noexcept
+{
+    JSON_ASSERT(digits >= powers_of_ten_16()[static_cast<std::size_t>(count - 1)] && count <= 15);
+    const int scale = 16 - count;
+    return write_shortest(first, zmij::shortest_decimal{digits * powers_of_ten_16()[static_cast<std::size_t>(scale)], exp - scale - 1, 0, false});
+}
+
+/// as write_short_decimal(), counting the digits (not 0, less than 10^15)
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_short_decimal(char* first, std::uint64_t digits, int exp) noexcept
+{
+    JSON_ASSERT(digits != 0 && digits < 1000000000000000u);
+    // floor(log10(2^bits)) + 1 digits, or one less
+    const int log2_bound = ((64 - count_leading_zeros(digits)) * 1233) >> 12;
+    const int count = log2_bound + (digits >= powers_of_ten_16()[static_cast<std::size_t>(log2_bound)] ? 1 : 0);
+    return write_short_decimal(first, digits, count, exp);
+}
+
 /*!
 @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)

include/nlohmann/detail/view/document_data.hpp

@@ -10,9 +10,11 @@
 
 #include <array> // array
 #include <cstddef> // size_t
-#include <cstdint> // uint32_t
+#include <cstdint> // uint8_t, uint32_t
 #include <cstring> // memcpy
 #include <limits> // numeric_limits
+#include <map> // map
+#include <memory> // unique_ptr
 #include <new> // bad_alloc, operator new, placement new
 #include <string> // string
 #include <vector> // vector
@@ -40,7 +42,9 @@ struct document_data
     std::size_t inline_capacity = 0;
     std::size_t max_depth = 0; ///< deepest nesting of arrays and objects (the root container is depth 1)
     std::vector<char> arena; ///< decoded strings that contained escapes (no terminator: they are handed out with their length)
+    std::size_t arena_size = 0; ///< bytes of decoded strings at base[1] (the arena, or those of a loaded image)
     std::string owned; ///< owned copy of the input, if any (a std::string, so that its NUL serves as the parser's sentinel)
+    std::vector<std::uint8_t> owned_image; ///< a loaded image the document owns (the text and the decoded strings point into it)
 
     // hash indexes of the keys of large objects (see object_index.hpp)
     static constexpr std::uint32_t index_min_members = 128;
@@ -52,9 +56,30 @@ struct document_data
     std::vector<object_index> indexes;
     std::vector<std::uint32_t> index_slots;
     std::vector<std::uint32_t> large_objects; ///< positions of the objects to index (noted while parsing)
-    std::array<const char*, 4> base = {{nullptr, nullptr, nullptr, nullptr}}; ///< string bases: source, arena (indexed by flags & node_flags::storage)
+    std::array<const char*, 4> base = {{nullptr, nullptr, nullptr, nullptr}}; ///< string bases: source, arena, edit arena (indexed by flags & node_flags::storage)
     bool discarded = true;
 
+    /// The storage of edits (editable documents only; see edit_storage.hpp).
+    /// Edits never move or resize the parsed index, so views stay valid: an
+    /// array/object whose elements change gets node_flags::moved, and its
+    /// elements then live in a separate sequence (a header node, then the
+    /// entries), whose entries link to the values.
+    struct edit_state
+    {
+        std::vector<node*> moved{};                    ///< element sequences of moved arrays/objects (header node first) // NOLINT(readability-redundant-member-init)
+        std::vector<std::size_t> moved_cap{};          ///< capacity in nodes of a growable block; 0: a fixed sequence (a new value) // NOLINT(readability-redundant-member-init)
+        std::vector<std::unique_ptr<node[]>> chunks{}; ///< storage of new values and blocks; never moved // NOLINT(readability-redundant-member-init,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+        std::map<const node*, node*> regions{}; ///< new arrays/objects: root -> container that uses it as its element sequence (nullptr: linked from a block) // NOLINT(readability-redundant-member-init)
+        node* chunk_cur = nullptr;
+        node* chunk_end = nullptr;
+        std::size_t chunk_next = 64;
+        std::vector<std::unique_ptr<char[]>> texts{}; ///< edit arena, the current buffer last; earlier ones stay alive for string views // NOLINT(readability-redundant-member-init,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+        std::size_t text_used = 0;
+        std::size_t text_cap = 0;
+        std::size_t bytes = 0; ///< memory held by edits
+    };
+    std::unique_ptr<edit_state> edits; ///< created by the first edit
+
     /// One allocation for the header and room for `count` nodes, so that a
     /// small document needs one allocation instead of two. Large documents get
     /// a separate node array instead (so it can be trimmed). When a document
@@ -94,9 +119,11 @@ struct document_data
     document_data() noexcept
         : arena() // NOLINT(readability-redundant-member-init)
         , owned() // NOLINT(readability-redundant-member-init)
+        , owned_image() // NOLINT(readability-redundant-member-init)
         , indexes() // NOLINT(readability-redundant-member-init)
         , index_slots() // NOLINT(readability-redundant-member-init)
         , large_objects() // NOLINT(readability-redundant-member-init)
+        , edits() // NOLINT(readability-redundant-member-init)
     {}
     document_data(const document_data&) = delete;
     document_data(document_data&&) = delete;
@@ -173,6 +200,90 @@ struct document_data
     {
         return n + n->next;
     }
+
+    /// (editable documents) first element or key, also of a moved container
+    NLOHMANN_VIEW_ALWAYS_INLINE const node* first_child_edited(const node* n) const noexcept
+    {
+        return NLOHMANN_VIEW_LIKELY((n->flags & node_flags::moved) == 0) ? n + 1 : edits->moved[n->off] + 1;
+    }
+
+    /// (editable documents) end of the elements, also of a moved container
+    NLOHMANN_VIEW_ALWAYS_INLINE const node* child_end_edited(const node* n) const noexcept
+    {
+        if (NLOHMANN_VIEW_LIKELY((n->flags & node_flags::moved) == 0))
+        {
+            return n + n->next;
+        }
+        const node* const h = edits->moved[n->off];
+        return h + h->next;
+    }
+
+    /// (editable documents) the value at an element position: entries of
+    /// moved sequences are links. The link case is out of line, so that this
+    /// compiles to a predicted branch rather than a select that delays the
+    /// following loads.
+    static NLOHMANN_VIEW_ALWAYS_INLINE const node* deref(const node* n) noexcept
+    {
+        return NLOHMANN_VIEW_LIKELY(n->kind != kind_link) ? n : follow_link(n);
+    }
+
+    static NLOHMANN_VIEW_NOINLINE const node* follow_link(const node* n) noexcept
+    {
+        return link_target(*n);
+    }
+};
+
+/// How the index is walked: views of read-only documents follow the node
+/// array alone and compile without any of the edit handling; views of
+/// editable documents also follow moved element sequences and links.
+template<bool Editable>
+struct navigation
+{
+    /// whether the walk follows edits (the template argument as a runtime
+    /// condition: `Editable && ...` is a constant condition for MSVC, C4127)
+    static NLOHMANN_VIEW_ALWAYS_INLINE bool editable() noexcept
+    {
+        return false;
+    }
+
+    static NLOHMANN_VIEW_ALWAYS_INLINE const node* first(const document_data& /*d*/, const node* n) noexcept
+    {
+        return n + 1;
+    }
+
+    static NLOHMANN_VIEW_ALWAYS_INLINE const node* end(const document_data& /*d*/, const node* n) noexcept
+    {
+        return n + n->next;
+    }
+
+    static NLOHMANN_VIEW_ALWAYS_INLINE const node* value(const node* n) noexcept
+    {
+        return n;
+    }
+};
+
+template<>
+struct navigation<true>
+{
+    static NLOHMANN_VIEW_ALWAYS_INLINE bool editable() noexcept
+    {
+        return true;
+    }
+
+    static NLOHMANN_VIEW_ALWAYS_INLINE const node* first(const document_data& d, const node* n) noexcept
+    {
+        return d.first_child_edited(n);
+    }
+
+    static NLOHMANN_VIEW_ALWAYS_INLINE const node* end(const document_data& d, const node* n) noexcept
+    {
+        return d.child_end_edited(n);
+    }
+
+    static NLOHMANN_VIEW_ALWAYS_INLINE const node* value(const node* n) noexcept
+    {
+        return document_data::deref(n);
+    }
 };
 
 }  // namespace view

include/nlohmann/detail/view/edit.hpp

@@ -0,0 +1,883 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <array> // array
+#include <cmath> // isinf, isnan
+#include <cstddef> // size_t
+#include <cstdint> // int64_t, uint8_t, uint32_t, uint64_t
+#include <cstring> // memcmp, memmove
+#include <limits> // numeric_limits
+#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>
+#include <nlohmann/detail/view/edit_storage.hpp>
+#include <nlohmann/detail/view/errors.hpp>
+#include <nlohmann/detail/view/lookup.hpp>
+#include <nlohmann/detail/view/macro_scope.hpp>
+#include <nlohmann/detail/view/node.hpp>
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+
+template<typename BasicJsonType, bool Editable>
+class basic_json_view;
+
+namespace detail
+{
+namespace view
+{
+
+/// the index of the first true condition (the number of conditions if none is)
+template<bool... Conditions>
+struct first_true : std::integral_constant<int, 0> {};
+
+template<bool... Conditions>
+struct first_true<false, Conditions...> : std::integral_constant < int, 1 + first_true<Conditions...>::value > {};
+
+/// Checks a string the way basic_json's serializer does when it writes it
+/// (type_error.316 with the same message), so that an editable document
+/// only holds valid UTF-8: the error is at the first byte that no
+/// well-formed sequence can continue with (Unicode, Table 3-7).
+inline void check_utf8(const char* s, std::size_t n)
+{
+    const auto* const p = reinterpret_cast<const unsigned char*>(s); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    const auto hex = [](unsigned char c)
+    {
+        constexpr const char* digits = "0123456789ABCDEF";
+        return std::string{digits[c >> 4u], digits[c & 0xFu]};
+    };
+    for (std::size_t i = 0; i < n;)
+    {
+        const unsigned char c = p[i];
+        if (c < 0x80)
+        {
+            ++i;
+            continue;
+        }
+        std::size_t len = 0;
+        unsigned char lo = 0x80;
+        unsigned char hi = 0xBF;
+        if (c >= 0xC2 && c <= 0xDF)
+        {
+            len = 2;
+        }
+        else if (c >= 0xE0 && c <= 0xEF)
+        {
+            len = 3;
+            lo = c == 0xE0 ? 0xA0 : 0x80;
+            hi = c == 0xED ? 0x9F : 0xBF;
+        }
+        else if (c >= 0xF0 && c <= 0xF4)
+        {
+            len = 4;
+            lo = c == 0xF0 ? 0x90 : 0x80;
+            hi = c == 0xF4 ? 0x8F : 0xBF;
+        }
+        else
+        {
+            throw_type_error(316, concat("invalid UTF-8 byte at index ", std::to_string(i), ": 0x", hex(c)));
+        }
+        for (std::size_t k = 1; k < len; ++k)
+        {
+            if (i + k == n)
+            {
+                throw_type_error(316, concat("incomplete UTF-8 string; last byte: 0x", hex(p[n - 1])));
+            }
+            const unsigned char b = p[i + k];
+            if (b < (k == 1 ? lo : 0x80) || b > (k == 1 ? hi : 0xBF))
+            {
+                throw_type_error(316, concat("invalid UTF-8 byte at index ", std::to_string(i + k), ": 0x", hex(b)));
+            }
+        }
+        i += len;
+    }
+}
+
+/*!
+@brief the edits of an editable basic_json_document
+
+Values are accepted as views (of any document), BasicJsonType values, and
+everything BasicJsonType can be constructed from. The source text is never
+written: new values go to storage owned by the document (see
+edit_storage.hpp).
+*/
+template<typename BasicJsonType, typename View>
+class editor
+{
+    using number_integer_t = typename BasicJsonType::number_integer_t;
+    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    using number_float_t = typename BasicJsonType::number_float_t;
+    using string_t = typename BasicJsonType::string_t;
+    using string_view_t = typename View::string_view_t;
+    using nav = navigation<true>;
+
+  public:
+    explicit editor(document_data& d) noexcept
+        : m_doc(d)
+    {}
+
+    /// replace a value; returns its view
+    template<typename V>
+    View set(const View& target, V&& value)
+    {
+        node* const slot = own(target);
+        const encoded e = encode(std::forward<V>(value));
+        assign(slot, e, nullptr, false);
+        return View(&m_doc, slot);
+    }
+
+    /// set a member (appended if missing; a null value becomes an object);
+    /// returns a view of the member value
+    template<typename V>
+    View set(const View& object, string_view_t key, V&& value)
+    {
+        node* const o = own(object);
+        if (o->kind != static_cast<std::uint8_t>(value_t::object) && o->kind != static_cast<std::uint8_t>(value_t::null))
+        {
+            throw_type_error(305, "cannot use operator[] with a string argument with ", object.type_name());
+        }
+        check_utf8(key.data(), key.size());
+        const encoded e = encode(std::forward<V>(value));
+        if (o->kind == static_cast<std::uint8_t>(value_t::null))
+        {
+            become_empty(o, value_t::object);
+        }
+        // an existing member: assign it (and drop later duplicates, so that
+        // lookups, iteration, and materialize() agree)
+        node* slot = nullptr;
+        bool duplicates = false;
+        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
+            }
+        }
+        if (slot != nullptr)
+        {
+            if (duplicates)
+            {
+                erase_members(o, key, true);
+            }
+            assign(slot, e, o, true);
+            return View(&m_doc, slot);
+        }
+        const node k = string_node(key.data(), key.size());
+        slot = new_slot(e);
+        node* const h = block_of(m_doc, o, 2);
+        h[h->next] = k;
+        make_link(h[h->next + 1], slot);
+        h->next += 2;
+        ++h->len;
+        ++o->len;
+        return View(&m_doc, slot);
+    }
+
+    /// assign an existing array element; returns a view of it
+    template<typename V>
+    View set(const View& array, std::size_t idx, V&& value)
+    {
+        node* const a = own(array);
+        if (a->kind != static_cast<std::uint8_t>(value_t::array))
+        {
+            throw_type_error(305, "cannot use operator[] with a numeric argument with ", array.type_name());
+        }
+        check_index(idx, a->len);
+        const encoded e = encode(std::forward<V>(value));
+        node* const slot = const_cast<node*>(nav::value(element_at<true>(m_doc, a, idx))); // NOLINT(cppcoreguidelines-pro-type-const-cast)
+        assign(slot, e, a, true);
+        return View(&m_doc, slot);
+    }
+
+    /// append to an array (a null value becomes an array); returns a view of
+    /// the new element
+    template<typename V>
+    View push_back(const View& array, V&& value)
+    {
+        node* const a = own(array);
+        if (a->kind != static_cast<std::uint8_t>(value_t::array) && a->kind != static_cast<std::uint8_t>(value_t::null))
+        {
+            throw_type_error(308, "cannot use push_back() with ", array.type_name());
+        }
+        const encoded e = encode(std::forward<V>(value));
+        if (a->kind == static_cast<std::uint8_t>(value_t::null))
+        {
+            become_empty(a, value_t::array);
+        }
+        node* const slot = new_slot(e);
+        node* const h = block_of(m_doc, a, 1);
+        make_link(h[h->next], slot);
+        ++h->next;
+        ++h->len;
+        ++a->len;
+        return View(&m_doc, slot);
+    }
+
+    /// insert into an array before position idx (idx <= size()); returns a
+    /// view of the new element
+    template<typename V>
+    View insert(const View& array, std::size_t idx, V&& value)
+    {
+        node* const a = own(array);
+        if (a->kind != static_cast<std::uint8_t>(value_t::array))
+        {
+            throw_type_error(309, "cannot use insert() with ", array.type_name());
+        }
+        check_index(idx, a->len + 1);
+        const encoded e = encode(std::forward<V>(value));
+        node* const slot = new_slot(e);
+        node* const h = block_of(m_doc, a, 1);
+        std::memmove(h + 2 + idx, h + 1 + idx, (h->next - 1 - idx) * sizeof(node));
+        make_link(h[1 + idx], slot);
+        ++h->next;
+        ++h->len;
+        ++a->len;
+        return View(&m_doc, slot);
+    }
+
+    /// remove all members with this key; returns their number
+    std::size_t erase(const View& object, string_view_t key)
+    {
+        node* const o = own(object);
+        if (o->kind != static_cast<std::uint8_t>(value_t::object))
+        {
+            throw_type_error(307, "cannot use erase() with ", object.type_name());
+        }
+        for (const node* k = nav::first(m_doc, o), *end = nav::end(m_doc, o); k != end; k = document_data::after(k + 1))
+        {
+            if (key_equals(*k, key))
+            {
+                return erase_members(o, key, false);
+            }
+        }
+        return 0;
+    }
+
+    /// remove an array element
+    void erase(const View& array, std::size_t idx)
+    {
+        node* const a = own(array);
+        if (a->kind != static_cast<std::uint8_t>(value_t::array))
+        {
+            throw_type_error(307, "cannot use erase() with ", array.type_name());
+        }
+        check_index(idx, a->len);
+        node* const h = block_of(m_doc, a, 0);
+        std::memmove(h + 1 + idx, h + 2 + idx, (h->next - 2 - idx) * sizeof(node));
+        --h->next;
+        --h->len;
+        --a->len;
+    }
+
+  private:
+    /// an encoded value: a scalar node, or the root of a new array/object
+    struct encoded
+    {
+        node scalar{};
+        node* region = nullptr;
+    };
+
+    /// the node of a view of this document
+    node* own(const View& v)
+    {
+        if (NLOHMANN_VIEW_UNLIKELY(v.m_doc != &m_doc || v.m_node == nullptr))
+        {
+            throw_invalid_iterator(202, "view does not belong to this document");
+        }
+        edit_state_of(m_doc);
+        return const_cast<node*>(v.m_node); // NOLINT(cppcoreguidelines-pro-type-const-cast): the nodes belong to this document
+    }
+
+    static void check_index(std::size_t idx, std::size_t limit)
+    {
+        if (idx >= limit)
+        {
+            throw_out_of_range(401, concat("array index ", std::to_string(idx), " is out of range"));
+        }
+    }
+
+    bool key_equals(const node& k, string_view_t key) const noexcept
+    {
+        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)
+    {
+        node* const h = block_of(m_doc, o, 0);
+        node* w = h + 1;
+        std::size_t erased = 0;
+        bool kept = false;
+        for (const node* r = h + 1, *end = h + h->next; r != end; r += 2)
+        {
+            const bool match = key_equals(*r, key);
+            if (match && (kept || !keep_first))
+            {
+                ++erased;
+                continue;
+            }
+            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);
+        h->len -= static_cast<std::uint32_t>(erased);
+        o->len -= static_cast<std::uint32_t>(erased);
+        return erased;
+    }
+
+    /// 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 = static_cast<std::uint8_t>(node_flags::is_new | linked);
+        n->next = 1;
+    }
+
+    /// Replace the value at slot; `parent` is the container whose elements
+    /// 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.nodes && 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). 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))
+                {
+                    block_of(m_doc, p, 0);
+                }
+            }
+            *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
+        // sequence still steps over it), and the elements come from the new
+        // sequence
+        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;
+        // (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;
+    }
+
+    /// a node for a new element (links point to it; it never moves)
+    node* new_slot(const encoded& e)
+    {
+        if (e.region != nullptr)
+        {
+            return e.region;
+        }
+        node* const s = alloc_nodes(m_doc, 1);
+        *s = e.scalar;
+        return s;
+    }
+
+    //////////////
+    // encoding //
+    //////////////
+
+    template<int N>
+    using encode_tag = std::integral_constant<int, N>;
+
+    template<typename T>
+    struct is_view : std::false_type {};
+
+    template<typename J, bool E>
+    struct is_view<basic_json_view<J, E>> : std::true_type {};
+
+    template<typename V>
+    encoded encode(V&& v)
+    {
+        using D = typename std::decay<V>::type;
+        return encode_impl(std::forward<V>(v), encode_tag<first_true<is_view<D>::value,
+                           std::is_same<D, BasicJsonType>::value,
+                           std::is_same<D, std::nullptr_t>::value,
+                           std::is_same<D, bool>::value,
+                           std::is_arithmetic<D>::value,
+                           std::is_convertible<const D&, string_view_t>::value>::value> {});
+    }
+
+    /// a view of any document (copied; nothing is shared with it)
+    template<typename J, bool E>
+    encoded encode_impl(const basic_json_view<J, E>& v, encode_tag<0> /*view*/)
+    {
+        if (NLOHMANN_VIEW_UNLIKELY(v.m_node == nullptr))
+        {
+            throw_type_error(302, "type must be a value, but is ", "discarded");
+        }
+        encoded r;
+        if (!is_container(*v.m_node))
+        {
+            r.scalar = copy_scalar(*v.m_doc, *v.m_node);
+            return r;
+        }
+        r.region = alloc_nodes(m_doc, count_nodes<E>(*v.m_doc, v.m_node));
+        fill_nodes<E>(*v.m_doc, v.m_node, r.region);
+        edit_state_of(m_doc).regions.emplace(r.region, nullptr);
+        return r;
+    }
+
+    encoded encode_impl(const BasicJsonType& j, encode_tag<1> /*json*/)
+    {
+        encoded r;
+        if (!j.is_structured())
+        {
+            r.scalar = json_scalar(j);
+            return r;
+        }
+        r.region = alloc_nodes(m_doc, count_nodes(j));
+        fill_nodes(j, r.region);
+        edit_state_of(m_doc).regions.emplace(r.region, nullptr);
+        return r;
+    }
+
+    encoded encode_impl(std::nullptr_t /*unused*/, encode_tag<2> /*null*/)
+    {
+        encoded r;
+        r.scalar = plain_node(value_t::null);
+        return r;
+    }
+
+    encoded encode_impl(bool b, encode_tag<3> /*boolean*/)
+    {
+        encoded r;
+        r.scalar = plain_node(value_t::boolean);
+        r.scalar.flags = static_cast<std::uint8_t>(r.scalar.flags | (b ? node_flags::is_true : 0));
+        return r;
+    }
+
+    template<typename T>
+    encoded encode_impl(T x, encode_tag<4> /*number*/)
+    {
+        encoded r;
+        r.scalar = number_node(x, std::integral_constant<int, first_true<std::is_floating_point<T>::value, std::is_signed<T>::value>::value> {});
+        return r;
+    }
+
+    template<typename T>
+    encoded encode_impl(const T& s, encode_tag<5> /*string*/)
+    {
+        const string_view_t sv(s);
+        check_utf8(sv.data(), sv.size());
+        encoded r;
+        r.scalar = string_node(sv.data(), sv.size());
+        return r;
+    }
+
+    template<typename T>
+    encoded encode_impl(T&& x, encode_tag<6> /*other*/)
+    {
+        return encode_impl(BasicJsonType(std::forward<T>(x)), encode_tag<1> {});
+    }
+
+    static node plain_node(value_t k) noexcept
+    {
+        node n{};
+        n.kind = static_cast<std::uint8_t>(k);
+        n.flags = node_flags::is_new;
+        return n;
+    }
+
+    template<typename T>
+    node number_node(T x, std::integral_constant<int, 0> /*floating-point*/)
+    {
+        return float_node(static_cast<number_float_t>(x));
+    }
+
+    template<typename T>
+    node number_node(T x, std::integral_constant<int, 1> /*signed*/)
+    {
+        return integer_node(static_cast<std::uint64_t>(static_cast<std::int64_t>(x)), value_t::number_integer);
+    }
+
+    template<typename T>
+    node number_node(T x, std::integral_constant<int, 2> /*unsigned*/)
+    {
+        return integer_node(static_cast<std::uint64_t>(x), value_t::number_unsigned);
+    }
+
+    /// an integer with its canonical token in the edit arena
+    node integer_node(std::uint64_t bits, value_t k)
+    {
+        const bool negative = k == value_t::number_integer && static_cast<std::int64_t>(bits) < 0;
+        std::uint64_t magnitude = negative ? 0 - bits : bits;
+        std::array<char, 24> buf{};
+        char* p = buf.data() + buf.size(); // NOLINT(misc-const-correctness): digits are written through p
+        do
+        {
+            *--p = static_cast<char>('0' + (magnitude % 10));
+            magnitude /= 10;
+        }
+        while (magnitude != 0);
+        if (negative)
+        {
+            *--p = '-';
+        }
+        const auto len = static_cast<std::size_t>(buf.data() + buf.size() - p);
+        node n = plain_node(k);
+        n.flags = static_cast<std::uint8_t>(n.flags | node_flags::edited);
+        n.off = append_text(m_doc, p, len);
+        // number_length() adds one for the sign of number_integer nodes
+        n.extra = static_cast<std::uint16_t>(k == value_t::number_integer ? len - 1 : len);
+        set_integer_bits(n, bits);
+        return n;
+    }
+
+    /// a float with its shortest round-trip token (as basic_json::dump()
+    /// writes it), or nan, inf, -inf, in the edit arena
+    node float_node(number_float_t x)
+    {
+        string_t text;
+        if (std::isnan(x))
+        {
+            text = "nan";
+        }
+        else if (std::isinf(x))
+        {
+            text = x > 0 ? "inf" : "-inf";
+        }
+        else
+        {
+            text = BasicJsonType(x).dump();
+        }
+        node n = plain_node(value_t::number_float);
+        n.flags = static_cast<std::uint8_t>(n.flags | node_flags::edited);
+        n.extra = 0xFFFFu; // (the digit layout is not recorded)
+        n.off = append_text(m_doc, text.data(), text.size());
+        n.len = static_cast<std::uint32_t>(text.size());
+        return n;
+    }
+
+    /// a string (or key) in the edit arena
+    node string_node(const char* s, std::size_t len)
+    {
+        if (NLOHMANN_VIEW_UNLIKELY(len >= 0xFFFFFFFFu))
+        {
+            throw_out_of_range(416, "strings of 4 GiB or more are not supported by json_document"); // LCOV_EXCL_LINE
+        }
+        node n = plain_node(value_t::string);
+        n.flags = static_cast<std::uint8_t>(n.flags | node_flags::edited);
+        n.off = append_text(m_doc, s, len);
+        n.len = static_cast<std::uint32_t>(len);
+        return n;
+    }
+
+    /// a scalar of a view (of any document) as a node of this document
+    node copy_scalar(const document_data& from, const node& n)
+    {
+        if (&from == &m_doc)
+        {
+            return n; // the same storage
+        }
+        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:
+                return integer_node(integer_bits(n), static_cast<value_t>(n.kind));
+            case value_t::number_float:
+            {
+                node r = plain_node(value_t::number_float);
+                r.flags = static_cast<std::uint8_t>(r.flags | node_flags::edited);
+                r.off = append_text(m_doc, from.str(n), n.len);
+                r.len = n.len;
+                r.extra = n.extra;
+                return r;
+            }
+            case value_t::boolean:
+            {
+                node r = plain_node(value_t::boolean);
+                r.flags = static_cast<std::uint8_t>(r.flags | (n.flags & node_flags::is_true));
+                return r;
+            }
+            case value_t::null:
+            case value_t::object:
+            case value_t::array:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
+                return plain_node(value_t::null);
+        }
+    }
+
+    node json_scalar(const BasicJsonType& j)
+    {
+        switch (j.type())
+        {
+            case value_t::null:
+                return plain_node(value_t::null);
+            case value_t::boolean:
+            {
+                node r = plain_node(value_t::boolean);
+                r.flags = static_cast<std::uint8_t>(r.flags | (j.template get<bool>() ? node_flags::is_true : 0));
+                return r;
+            }
+            case value_t::number_integer:
+                return integer_node(static_cast<std::uint64_t>(static_cast<std::int64_t>(j.template get<number_integer_t>())), value_t::number_integer);
+            case value_t::number_unsigned:
+                return integer_node(static_cast<std::uint64_t>(j.template get<number_unsigned_t>()), value_t::number_unsigned);
+            case value_t::number_float:
+                return float_node(j.template get<number_float_t>());
+            case value_t::string:
+            {
+                const auto& s = j.template get_ref<const string_t&>();
+                check_utf8(s.data(), s.size());
+                return string_node(s.data(), s.size());
+            }
+            case value_t::binary:
+                throw_type_error(319, "cannot store a binary value in a json_document", "");
+            case value_t::discarded:
+            case value_t::object:
+            case value_t::array:
+            default:
+                throw_type_error(302, "type must be a value, but is ", "discarded");
+        }
+    }
+
+    // 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)
+    {
+        using walk = navigation<E>;
+        struct frame
+        {
+            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 (;;)
+        {
+            ++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;
+            }
+        }
+    }
+
+    /// copy a subtree (of any document) as a contiguous sequence of
+    /// count_nodes() nodes
+    template<bool E>
+    void fill_nodes(const document_data& d, const node* n, node* out)
+    {
+        using walk = navigation<E>;
+        struct frame
+        {
+            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 (is_container(*n))
+            {
+                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;
+            }
+        }
+    }
+
+    static std::size_t count_nodes(const BasicJsonType& j)
+    {
+        using iterator = typename BasicJsonType::const_iterator;
+        struct frame
+        {
+            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())
+            {
+                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;
+            }
+        }
+    }
+
+    void fill_nodes(const BasicJsonType& j, node* out)
+    {
+        using iterator = typename BasicJsonType::const_iterator;
+        struct frame
+        {
+            iterator pos;
+            iterator end;
+            bool object;
+            node* self; ///< the container in the copy
+        };
+        std::vector<frame> open;
+        const BasicJsonType* n = &j;
+        for (;;)
+        {
+            if (n->is_structured())
+            {
+                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;
+            }
+        }
+    }
+
+    document_data& m_doc;
+};
+
+}  // namespace view
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/view/edit_storage.hpp

@@ -0,0 +1,266 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <algorithm> // max, min
+#include <cstddef> // size_t
+#include <cstdint> // uint8_t, uint32_t
+#include <cstring> // memcpy
+#include <functional> // less
+#include <memory> // unique_ptr
+#include <utility> // move
+
+#include <nlohmann/json.hpp>
+#include <nlohmann/detail/view/document_data.hpp>
+#include <nlohmann/detail/view/errors.hpp>
+#include <nlohmann/detail/view/macro_scope.hpp>
+#include <nlohmann/detail/view/node.hpp>
+
+// The storage of edits. Edits never move or resize the parsed index: every
+// value keeps its node, so views stay valid. New values and element sequences
+// live in chunks that never move; strings and number tokens written by edits
+// live in the edit arena. An array/object whose elements change gets
+// node_flags::moved: its elements then live in a separate sequence (a header
+// node, then the entries), whose entries link to the values (kind_link).
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+namespace view
+{
+
+inline document_data::edit_state& edit_state_of(document_data& d)
+{
+    if (!d.edits)
+    {
+        d.edits.reset(new document_data::edit_state()); // NOLINT(cppcoreguidelines-owning-memory,modernize-make-unique): owned by the unique_ptr; std::make_unique is C++14
+    }
+    return *d.edits;
+}
+
+/// k consecutive nodes that never move (new values and blocks)
+inline node* alloc_nodes(document_data& d, std::size_t k)
+{
+    document_data::edit_state& e = edit_state_of(d);
+    if (NLOHMANN_VIEW_UNLIKELY(static_cast<std::size_t>(e.chunk_end - e.chunk_cur) < k))
+    {
+        const std::size_t count = (std::max)(k, e.chunk_next);
+        std::unique_ptr<node[]> fresh(new node[count]()); // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+        e.chunks.push_back(std::move(fresh));
+        e.chunk_cur = e.chunks.back().get();
+        e.chunk_end = e.chunk_cur + count;
+        e.chunk_next = (std::min)(e.chunk_next * 2, std::size_t{65536});
+        e.bytes += count * sizeof(node);
+    }
+    node* const r = e.chunk_cur;
+    e.chunk_cur += 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)
+{
+    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 = 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)
+        {
+            std::memcpy(fresh.get(), e.texts.back().get(), e.text_used);
+        }
+        e.texts.push_back(std::move(fresh));
+        e.text_cap = cap;
+        e.bytes += cap;
+        d.base[2] = e.texts.back().get();
+    }
+    const auto off = static_cast<std::uint32_t>(e.text_used);
+    if (n != 0)
+    {
+        std::memcpy(e.texts.back().get() + e.text_used, s, n);
+    }
+    e.text_used += n;
+    return off;
+}
+
+/// the capacity in nodes of the block of a moved container (0: a fixed
+/// sequence, the elements of a new value)
+inline std::size_t moved_capacity(const document_data& d, const node* n) noexcept
+{
+    return d.edits->moved_cap[n->off];
+}
+
+/// 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 (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
+    }
+    if (e.moved.size() == e.moved.capacity() || e.moved_cap.size() == e.moved_cap.capacity())
+    {
+        // both grow before either changes, so that the push_backs cannot throw
+        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);
+    n->flags = static_cast<std::uint8_t>(n->flags | node_flags::moved | node_flags::is_new);
+}
+
+/// Make the elements of container n a growable block with room for `extra`
+/// more nodes, and return its header. The entries link to the existing
+/// values, which stay where they are. A block that grows is copied (its old
+/// space is not reused).
+inline node* block_of(document_data& d, node* n, std::size_t extra)
+{
+    if ((n->flags & node_flags::moved) != 0 && moved_capacity(d, n) != 0)
+    {
+        node* const h = d.edits->moved[n->off];
+        if (h->next + extra <= moved_capacity(d, n))
+        {
+            return h;
+        }
+        const std::size_t cap = (std::max)(2 * moved_capacity(d, n), h->next + extra);
+        node* const nh = alloc_nodes(d, cap);
+        std::memcpy(nh, h, h->next * sizeof(node));
+        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;
+    node* const h = alloc_nodes(d, cap);
+    *h = node{};
+    h->kind = n->kind;
+    h->len = n->len;
+    h->next = static_cast<std::uint32_t>(used);
+    node* o = h + 1;
+    for (const node* c = d.first_child_edited(n), *e = d.child_end_edited(n); c != e;)
+    {
+        if (object)
+        {
+            *o++ = *c++; // the key
+        }
+        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);
+    }
+    set_moved(d, n, h, cap);
+    return h;
+}
+
+/// The container whose elements include `target`; nullptr for the root, for
+/// a value that is no longer part of the document, and for a value that is
+/// only reached through a link. Values never move between allocations, so
+/// the path to `target` stays inside the allocation that holds it (the parsed
+/// index, or one new value), where the extent of each container (`next`)
+/// still covers its original subtree.
+inline node* find_parent(const document_data& d, const node* target)
+{
+    const std::less<const node*> lt{};
+    const node* lo = d.nodes;
+    const node* hi = d.nodes + d.node_count;
+    const node* c = d.nodes;
+    if (lt(target, lo) || !lt(target, hi))
+    {
+        if (!d.edits)
+        {
+            return nullptr; // LCOV_EXCL_LINE (nodes outside the index exist only after edits)
+        }
+        auto it = d.edits->regions.upper_bound(target);
+        if (it == d.edits->regions.begin())
+        {
+            return nullptr; // LCOV_EXCL_LINE (an array/object with elements is in the index or a new value)
+        }
+        --it;
+        lo = it->first;
+        hi = lo + lo->next;
+        if (!lt(target, hi))
+        {
+            return nullptr; // LCOV_EXCL_LINE (a single-node value, reached through a link)
+        }
+        // the root of a new value is the element sequence of its owner, or a linked value
+        c = it->second != nullptr ? it->second : lo;
+    }
+    if (target == lo)
+    {
+        return nullptr;
+    }
+    for (;;)
+    {
+        if (!is_container(*c))
+        {
+            return nullptr; // LCOV_EXCL_LINE (the value is inside c)
+        }
+        const bool object = c->kind == static_cast<std::uint8_t>(value_t::object);
+        const node* down = nullptr;
+        for (const node* p = d.first_child_edited(c), *e = d.child_end_edited(c); p != e;)
+        {
+            const node* const at = object ? p + 1 : p;
+            const node* const v = document_data::deref(at);
+            if (v == target)
+            {
+                return const_cast<node*>(c); // NOLINT(cppcoreguidelines-pro-type-const-cast): the nodes belong to the document
+            }
+            if (is_container(*v) && !lt(v, lo) && lt(v, target) && lt(target, v + v->next))
+            {
+                down = v;
+                break;
+            }
+            p = document_data::after(at);
+        }
+        if (down == nullptr)
+        {
+            return nullptr;
+        }
+        c = down;
+    }
+}
+
+}  // namespace view
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/view/errors.hpp

@@ -30,6 +30,11 @@ namespace view
     NLOHMANN_VIEW_THROW(type_error::create(id, concat(prefix, type), nullptr));
 }
 
+[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_type_error(int id, const std::string& msg)
+{
+    NLOHMANN_VIEW_THROW(type_error::create(id, msg, nullptr));
+}
+
 [[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_out_of_range(int id, const std::string& msg)
 {
     NLOHMANN_VIEW_THROW(out_of_range::create(id, msg, nullptr));

include/nlohmann/detail/view/image.hpp

@@ -0,0 +1,755 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <algorithm> // sort
+#include <array> // array
+#include <cstddef> // size_t
+#include <cstdint> // int64_t, uint8_t, uint16_t, uint32_t, uint64_t
+#include <cstring> // memcmp, memcpy
+#include <limits> // numeric_limits
+#include <string> // string
+#include <vector> // vector
+
+#include <nlohmann/json.hpp>
+#include <nlohmann/detail/view/document_data.hpp>
+#include <nlohmann/detail/view/errors.hpp>
+#include <nlohmann/detail/view/macro_scope.hpp>
+#include <nlohmann/detail/view/node.hpp>
+#include <nlohmann/detail/view/number.hpp>
+#include <nlohmann/detail/view/object_index.hpp>
+#include <nlohmann/detail/view/scan.hpp>
+
+// Images: a document stored so that loading it needs no parsing.
+//
+// Layout (little-endian): a 64-byte header, the nodes, the text (the source,
+// followed by the number tokens written by edits), a NUL, the decoded strings
+// (followed by the strings written by edits), a NUL. The idea is that of
+// zero-copy formats such as FlatBuffers (https://github.com/google/flatbuffers)
+// and YaFF (https://github.com/yandex/yaff); no code is taken from them.
+// check_image follows the idea of FlatBuffers' Verifier (bounds and
+// structure) and also checks what the parser guarantees about strings and
+// numbers, so that reading and serializing a checked image is safe and yields
+// valid JSON.
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+namespace view
+{
+
+/// how load() checks an image
+enum class image_check
+{
+    /// everything the parser guarantees: structure and bounds, strings (valid
+    /// UTF-8; source strings without quotes, backslashes, and control
+    /// characters), and numbers (well-formed, matching the stored values)
+    full,
+    /// structure and bounds only: reading and serializing are safe, but a
+    /// crafted image can yield invalid UTF-8, strings that serialize to
+    /// invalid JSON, or numbers that differ from their text
+    bounds,
+    /// none: for images from a trusted source only (a damaged image is
+    /// undefined behavior)
+    none,
+};
+
+struct image_header
+{
+    std::array<char, 4> magic;              ///< "NJVI"
+    std::uint32_t version;                  ///< 1
+    std::uint64_t node_count;
+    std::uint64_t text_size;
+    std::uint64_t arena_size;
+    std::array<std::uint64_t, 4> reserved;  ///< zero (for later versions)
+};
+static_assert(sizeof(image_header) == 64, "the image header must be 64 bytes");
+
+constexpr std::uint32_t image_version = 1;
+
+/// the largest node count and text or string size of an image (as for parsed
+/// documents, offsets and counts must fit 32 bits)
+constexpr std::uint64_t image_limit = 0xFFFFFFF0u;
+
+/// Copy the current structure of an edited document into nodes in document
+/// order, as the parser would have written them. Text written by edits is
+/// appended to text_tail (number tokens) and arena_tail (strings); floats that
+/// are not finite become null, as dump() writes them.
+inline void compact_nodes(const document_data& d, std::size_t arena_size, std::vector<node>& out, std::string& text_tail, std::string& arena_tail)
+{
+    struct frame
+    {
+        const node* cur;
+        const node* end;
+        std::size_t index; ///< the container's node in out
+        std::uint32_t count;
+        bool object;
+    };
+    std::vector<frame> stack;
+    const auto string_node = [&](const node & s)
+    {
+        node r = s;
+        r.extra = 0;
+        r.flags = static_cast<std::uint8_t>(s.flags & node_flags::storage);
+        if (r.flags == node_flags::edited)
+        {
+            r.off = static_cast<std::uint32_t>(arena_size + arena_tail.size());
+            arena_tail.append(d.str(s), s.len);
+            r.flags = node_flags::escaped;
+        }
+        return r;
+    };
+    const auto copy_node = [&](const node * v)
+    {
+        node r = *v;
+        switch (static_cast<value_t>(v->kind))
+        {
+            case value_t::object:
+            case value_t::array:
+                r.flags = 0;
+                r.extra = 0;
+                r.off = (v->flags & (node_flags::moved | node_flags::is_new)) != 0 ? 0 : v->off;
+                r.len = 0;  // counted below
+                r.next = 0; // set when the container is complete
+                stack.push_back(frame{d.first_child_edited(v), d.child_end_edited(v), out.size(), 0, v->kind == static_cast<std::uint8_t>(value_t::object)});
+                break;
+            case value_t::string:
+                r = string_node(*v);
+                break;
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+                if ((v->flags & node_flags::storage) == node_flags::edited)
+                {
+                    r.off = static_cast<std::uint32_t>(d.size + text_tail.size());
+                    text_tail.append(d.str(*v), number_length(*v));
+                }
+                r.flags = 0;
+                break;
+            case value_t::number_float:
+                if ((v->flags & node_flags::storage) == node_flags::edited)
+                {
+                    const char* const t = d.str(*v);
+                    if (t[0] == 'n' || t[0] == 'i' || (v->len > 1 && t[1] == 'i'))
+                    {
+                        r = node{}; // nan and infinity: null, as dump() writes them
+                        r.kind = static_cast<std::uint8_t>(value_t::null);
+                        break;
+                    }
+                    r.off = static_cast<std::uint32_t>(d.size + text_tail.size());
+                    text_tail.append(t, v->len);
+                    r.extra = 0xFFFFu; // the digit layout is not recorded
+                }
+                r.flags = 0;
+                break;
+            case value_t::boolean:
+                r.flags = static_cast<std::uint8_t>(v->flags & node_flags::is_true);
+                break;
+            case value_t::null:
+            case value_t::binary:
+            case value_t::discarded:
+            default:
+                r.flags = 0;
+                break;
+        }
+        out.push_back(r);
+    };
+    copy_node(d.nodes);
+    while (!stack.empty())
+    {
+        frame& top = stack.back();
+        if (top.cur == top.end)
+        {
+            node& c = out[top.index];
+            c.len = top.count;
+            c.next = static_cast<std::uint32_t>(out.size() - top.index);
+            stack.pop_back();
+            continue;
+        }
+        ++top.count;
+        const node* v = nullptr;
+        if (top.object)
+        {
+            out.push_back(string_node(*top.cur));
+            v = document_data::deref(top.cur + 1);
+            top.cur = document_data::after(top.cur + 1);
+        }
+        else
+        {
+            v = document_data::deref(top.cur);
+            top.cur = document_data::after(top.cur);
+        }
+        copy_node(v); // may grow the stack (top is not used afterwards)
+    }
+}
+
+/// the document as an image
+inline std::vector<std::uint8_t> save_image(const document_data& d)
+{
+#if !NLOHMANN_VIEW_LITTLE_ENDIAN
+    throw_type_error(320, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
+#endif
+    const std::size_t arena_size = d.arena_size;
+    const node* nodes = d.nodes;
+    std::size_t count = d.node_count;
+    std::vector<node> compacted;
+    std::string text_tail;
+    std::string arena_tail;
+    if (d.edits)
+    {
+        compact_nodes(d, arena_size, compacted, text_tail, arena_tail);
+        nodes = compacted.data();
+        count = compacted.size();
+    }
+    const std::size_t text_size = d.size + text_tail.size();
+    const std::size_t total_arena = arena_size + arena_tail.size();
+    if (NLOHMANN_VIEW_UNLIKELY(text_size >= image_limit || total_arena >= image_limit || count >= image_limit))
+    {
+        // LCOV_EXCL_START (4 GiB)
+        throw_out_of_range(416, "images of 4 GiB or more are not supported by json_document");
+        // LCOV_EXCL_STOP
+    }
+    image_header h{};
+    h.magic = {{'N', 'J', 'V', 'I'}};
+    h.version = image_version;
+    h.node_count = count;
+    h.text_size = text_size;
+    h.arena_size = total_arena;
+    std::vector<std::uint8_t> image(sizeof(h) + (count * sizeof(node)) + text_size + 1 + total_arena + 1);
+    std::uint8_t* o = image.data();
+    std::memcpy(o, &h, sizeof(h));
+    o += sizeof(h);
+    std::memcpy(o, nodes, count * sizeof(node));
+    // the hash indexes are rebuilt by load()
+    for (std::size_t i = 0; i < count; ++i)
+    {
+        if (nodes[i].kind == static_cast<std::uint8_t>(value_t::object) && nodes[i].extra != 0)
+        {
+            node n = nodes[i];
+            n.extra = 0;
+            std::memcpy(o + (i * sizeof(node)), &n, sizeof(node));
+        }
+    }
+    o += count * sizeof(node);
+    const auto append = [&o](const char* s, std::size_t n)
+    {
+        if (n != 0)
+        {
+            std::memcpy(o, s, n);
+            o += n;
+        }
+    };
+    append(d.src, d.size);
+    append(text_tail.data(), text_tail.size());
+    *o++ = 0;
+    append(d.base[1], arena_size);
+    append(arena_tail.data(), arena_tail.size());
+    *o = 0;
+    return image;
+}
+
+/// 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 unsigned char* const e = s + len;
+    const unsigned char* p = s;
+    t.negative = p != e && *p == '-';
+    p += t.negative ? 1 : 0;
+    t.int_start = p;
+    if (p == e)
+    {
+        return false;
+    }
+    if (*p == '0')
+    {
+        ++p;
+    }
+    else if (*p >= '1' && *p <= '9')
+    {
+        while (p != e && is_digit(*p))
+        {
+            ++p;
+        }
+    }
+    else
+    {
+        return 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;
+        while (p != e && is_digit(*p))
+        {
+            ++p;
+        }
+        if (p == f0)
+        {
+            return false;
+        }
+        t.frac_digits = static_cast<std::size_t>(p - f0);
+        t.is_float = true;
+    }
+    t.exponent = 0;
+    if (p != e && (*p | 0x20u) == 'e')
+    {
+        ++p;
+        const bool exp_negative = p != e && *p == '-';
+        p += (p != e && (*p == '+' || *p == '-')) ? 1 : 0;
+        if (p == e || !is_digit(*p))
+        {
+            return false;
+        }
+        while (p != e && is_digit(*p))
+        {
+            t.exponent = t.exponent < 100000 ? (t.exponent * 10) + (*p - '0') : t.exponent;
+            ++p;
+        }
+        t.exponent = exp_negative ? -t.exponent : t.exponent;
+        t.is_float = true;
+    }
+    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;
+    }
+    // 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 (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 (t.int_digits == 20 && std::memcmp(t.int_start, "18446744073709551615", 20) > 0)
+    {
+        return false;
+    }
+    std::uint64_t m = 0;
+    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 > (t.negative ? std::uint64_t{1} << 63u : (std::uint64_t{1} << 63u) - 1))
+    {
+        return false;
+    }
+    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)
+    {
+        if (a.off != b.off)
+        {
+            return a.off < b.off;
+        }
+        if (a.len != b.len)
+        {
+            return a.len < b.len;
+        }
+        return 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:
+/// kinds, flags, and `extra`; extents and element counts of arrays and
+/// 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)
+{
+    struct frame
+    {
+        std::size_t end;
+        std::uint32_t len;
+        std::uint32_t seen;
+        bool object;
+        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)
+        {
+            return false;
+        }
+        const bool decoded = (n.flags & node_flags::escaped) != 0;
+        const std::size_t limit = decoded ? arena_size : text_size;
+        if (n.off > limit || n.len > limit - n.off)
+        {
+            return false;
+        }
+        if (full && n.len != 0)
+        {
+            (decoded ? decoded_strings : source_strings).push_back(byte_range{n.off, 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
+    {
+        const std::size_t len = number_length(n);
+        if (len == 0 || n.off > text_size || len > text_size - n.off)
+        {
+            return false;
+        }
+        if (n.kind != static_cast<std::uint8_t>(value_t::number_float))
+        {
+            return (n.extra >> 8u) == 0;
+        }
+        // float_value() reads the sign, the integer digits, and the point and
+        // fraction digits the layout records (a layout of more than 19 digits
+        // means the general conversion, which stays within the token)
+        const std::size_t int_digits = n.extra & 0xFFu;
+        const std::size_t frac_digits = n.extra >> 8u;
+        const std::size_t need = (text[n.off] == '-' ? 1u : 0u) + int_digits + (frac_digits != 0 ? frac_digits + 1 : 0);
+        return int_digits + frac_digits > 19 || need <= len;
+    };
+    std::size_t i = 0;
+    for (;;)
+    {
+        // close finished arrays and objects
+        while (!stack.empty() && i == stack.back().end)
+        {
+            const frame f = stack.back();
+            if (f.seen != f.len || (f.object && !f.expect_key))
+            {
+                return false;
+            }
+            stack.pop_back();
+            if (!stack.empty())
+            {
+                ++stack.back().seen;
+                stack.back().expect_key = true;
+            }
+        }
+        if (i == count)
+        {
+            return stack.empty() && (!full || check_contents(text, arena, source_strings, decoded_strings, floats));
+        }
+        if (i != 0 && stack.empty())
+        {
+            return false; // nodes after the root
+        }
+        const node& n = nodes[i];
+        if (!stack.empty() && stack.back().object && stack.back().expect_key)
+        {
+            if (n.kind != static_cast<std::uint8_t>(value_t::string) || !check_string(n))
+            {
+                return false;
+            }
+            stack.back().expect_key = false;
+            ++i;
+            continue;
+        }
+        bool complete = true;
+        switch (static_cast<value_t>(n.kind))
+        {
+            case value_t::null:
+                // (the offset of a literal is read to size the output of dump())
+                if (n.flags != 0 || n.extra != 0 || n.off > text_size)
+                {
+                    return false;
+                }
+                break;
+            case value_t::boolean:
+                if ((n.flags & ~node_flags::is_true) != 0 || n.extra != 0 || n.off > text_size)
+                {
+                    return false;
+                }
+                break;
+            case value_t::string:
+                if (!check_string(n))
+                {
+                    return false;
+                }
+                break;
+            case value_t::number_integer:
+            case value_t::number_unsigned:
+            case value_t::number_float:
+                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:
+            {
+                const std::size_t limit = stack.empty() ? count : stack.back().end;
+                if (n.flags != 0 || n.extra != 0 || n.next == 0 || n.next > limit - i || n.off > text_size)
+                {
+                    return false;
+                }
+                stack.push_back(frame{i + n.next, n.len, 0, n.kind == static_cast<std::uint8_t>(value_t::object), true});
+                complete = false;
+                break;
+            }
+            case value_t::binary:
+            case value_t::discarded:
+            default:
+                return false;
+        }
+        ++i;
+        if (complete && !stack.empty())
+        {
+            ++stack.back().seen;
+            stack.back().expect_key = true;
+        }
+    }
+}
+
+[[noreturn]] NLOHMANN_VIEW_NOINLINE inline void throw_invalid_image(const char* what)
+{
+    throw_parse_error(116, concat("invalid json_document image: ", what));
+}
+
+/// Read an image into d. The text and the decoded strings stay in the image;
+/// the nodes are copied (so that they are aligned, and edits can change them).
+inline void load_image(document_data& d, const std::uint8_t* image, std::size_t size, image_check check)
+{
+#if !NLOHMANN_VIEW_LITTLE_ENDIAN
+    throw_type_error(320, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
+#endif
+    if (image == nullptr || size < sizeof(image_header))
+    {
+        throw_invalid_image("too short");
+    }
+    image_header h{};
+    std::memcpy(&h, image, sizeof(h));
+    // (the reserved fields are for later versions)
+    if (std::memcmp(h.magic.data(), "NJVI", 4) != 0 || h.version != image_version
+            || (h.reserved[0] | h.reserved[1] | h.reserved[2] | h.reserved[3]) != 0)
+    {
+        throw_invalid_image("unknown format");
+    }
+    const std::size_t room = size - sizeof(h);
+    if (h.node_count == 0 || h.node_count > room / sizeof(node) || h.node_count >= image_limit || h.text_size >= image_limit || h.arena_size >= image_limit)
+    {
+        throw_invalid_image("sizes out of range");
+    }
+    const auto count = static_cast<std::size_t>(h.node_count);
+    const auto text_size = static_cast<std::size_t>(h.text_size);
+    const auto arena_size = static_cast<std::size_t>(h.arena_size);
+    const std::size_t text_at = sizeof(h) + (count * sizeof(node));
+    // the text, a NUL, the decoded strings, a NUL, and nothing after them
+    if (size - text_at < 2 || text_size > size - text_at - 2 || arena_size != size - text_at - text_size - 2
+            || image[text_at + text_size] != 0 || image[size - 1] != 0)
+    {
+        throw_invalid_image("sizes out of range");
+    }
+
+    d.discarded = true;
+    d.edits.reset();
+    d.base[2] = nullptr;
+    d.owned.clear();
+    if (d.owned_image.empty() || image != d.owned_image.data())
+    {
+        d.owned_image.clear();
+    }
+    d.arena.clear();
+    d.indexes.clear();
+    d.index_slots.clear();
+    d.large_objects.clear();
+    d.node_count = 0;
+    d.reserve(count);
+    std::memcpy(d.nodes, image + sizeof(h), count * sizeof(node));
+    d.node_count = count;
+    const std::uint8_t* const text = image + text_at;
+    const std::uint8_t* const arena = text + text_size + 1;
+    d.src = reinterpret_cast<const char*>(text); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    d.size = text_size;
+    d.base[0] = d.src;
+    d.base[1] = reinterpret_cast<const char*>(arena); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    d.arena_size = arena_size;
+    if (check != image_check::none && !check_image(d.nodes, count, text, text_size, arena, arena_size, check == image_check::full))
+    {
+        throw_invalid_image("the check failed");
+    }
+    // the hash indexes of large objects, as after parsing
+    for (std::size_t i = 0; i < count; ++i)
+    {
+        node& n = d.nodes[i];
+        if (n.kind == static_cast<std::uint8_t>(value_t::object))
+        {
+            n.extra = 0;
+            if (n.len >= document_data::index_min_members)
+            {
+                d.large_objects.push_back(static_cast<std::uint32_t>(i));
+            }
+        }
+    }
+    build_object_indexes(d);
+    std::vector<std::uint32_t>().swap(d.large_objects); // (only needed while building)
+    d.discarded = false;
+}
+
+}  // namespace view
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/view/iterator.hpp

@@ -73,7 +73,7 @@ class view_iterator
 
     NLOHMANN_VIEW_ALWAYS_INLINE View operator*() const noexcept
     {
-        return View(m_doc, m_pos + m_value_offset);
+        return View(m_doc, View::navigation::value(m_pos + m_value_offset));
     }
 
     pointer operator->() const noexcept

include/nlohmann/detail/view/lookup.hpp

@@ -88,18 +88,20 @@ class short_key
 /// nullptr (the search stops at the first match; materialize() and parse()
 /// keep the last value of a duplicate key instead); most keys are rejected by
 /// their length, from the index alone
-inline const node* find_member(const document_data& d, const node* object, const char* key, std::size_t n) noexcept
+template<bool Editable>
+const node* find_member(const document_data& d, const node* object, const char* key, std::size_t n) noexcept
 {
-    if (NLOHMANN_VIEW_UNLIKELY(object->extra != 0))
+    using nav = navigation<Editable>;
+    if (NLOHMANN_VIEW_UNLIKELY(object->extra != 0) && (!nav::editable() || (object->flags & node_flags::moved) == 0))
     {
-        return find_indexed(d, object, key, n); // a large object
+        return find_indexed(d, object, key, n); // a large object (whose members have not been edited)
     }
-    const node* const end = document_data::child_end(object);
+    const node* const end = nav::end(d, object);
     const auto* const k = reinterpret_cast<const unsigned char*>(key); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
     if (NLOHMANN_VIEW_LIKELY(n <= 16))
     {
         const short_key probe(k, n);
-        for (const node* m = document_data::first_child(object); m != end; m = document_data::after(m + 1))
+        for (const node* m = nav::first(d, object); m != end; m = document_data::after(m + 1))
         {
             if (m->len == n && probe.matches(reinterpret_cast<const unsigned char*>(d.str(*m)))) // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
             {
@@ -108,7 +110,7 @@ inline const node* find_member(const document_data& d, const node* object, const
         }
         return nullptr;
     }
-    for (const node* m = document_data::first_child(object); m != end; m = document_data::after(m + 1))
+    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)
         {
@@ -119,11 +121,13 @@ inline const node* find_member(const document_data& d, const node* object, const
 }
 
 /// the number of members of an object with this key (duplicates included)
-inline std::size_t count_members(const document_data& d, const node* object, const char* key, std::size_t n) noexcept
+template<bool Editable>
+std::size_t count_members(const document_data& d, const node* object, const char* key, std::size_t n) noexcept
 {
+    using nav = navigation<Editable>;
     std::size_t result = 0;
-    const node* const end = document_data::child_end(object);
-    for (const node* m = document_data::first_child(object); m != end; m = document_data::after(m + 1))
+    const node* const end = nav::end(d, object);
+    for (const node* m = nav::first(d, object); m != end; m = document_data::after(m + 1))
     {
         if (m->len == n && (n == 0 || std::memcmp(d.str(*m), key, n) == 0))
         {
@@ -151,10 +155,17 @@ SizeType to_index(IntegerType idx) noexcept
     return (idx < zero || static_cast<IntegerType>(result) != idx) ? (std::numeric_limits<SizeType>::max)() : result;
 }
 
-/// the element of an array at an index below its size
-inline const node* element_at(const node* array, std::size_t idx) noexcept
+/// the entry of the element of an array at an index below its size (a link
+/// in the moved sequences of editable documents)
+template<bool Editable>
+const node* element_at(const document_data& d, const node* array, std::size_t idx) noexcept
 {
-    const node* e = document_data::first_child(array);
+    using nav = navigation<Editable>;
+    const node* e = nav::first(d, array);
+    if (nav::editable() && (array->flags & node_flags::moved) != 0 && d.edits->moved_cap[array->off] != 0)
+    {
+        return e + idx; // a growable block: one link per element
+    }
     for (std::size_t i = 0; i < idx; ++i)
     {
         e = document_data::after(e);
@@ -162,13 +173,14 @@ inline const node* element_at(const node* array, std::size_t idx) noexcept
     return e;
 }
 
-/// the last element of a non-empty array, or the key of the last member of a
-/// non-empty object
-inline const node* last_child(const node* container) noexcept
+/// the entry of the last element of a non-empty array, or the key of the
+/// last member of a non-empty object
+template<bool Editable>
+const node* last_child(const document_data& d, const node* container) noexcept
 {
     const std::size_t value_offset = container->kind == static_cast<std::uint8_t>(value_t::object) ? 1 : 0;
-    const node* const end = document_data::child_end(container);
-    const node* last = document_data::first_child(container);
+    const node* const end = navigation<Editable>::end(d, container);
+    const node* last = navigation<Editable>::first(d, container);
     for (const node* c = document_data::after(last + value_offset); c != end; c = document_data::after(c + value_offset))
     {
         last = c;

include/nlohmann/detail/view/materialize.hpp

@@ -36,26 +36,32 @@ iterative, so the nesting depth is limited by memory only, as for parse().
 Without a lexer the handler records no source positions
 (JSON_DIAGNOSTIC_POSITIONS).
 */
-template<typename BasicJsonType>
+template<typename BasicJsonType, bool Editable>
 BasicJsonType materialize(const document_data& d, const node* n)
 {
     using string_t = typename BasicJsonType::string_t;
     using sax_t = json_sax_dom_parser<BasicJsonType, iterator_input_adapter<const char*>>;
+    using nav = navigation<Editable>;
+
+    // the open containers: their next element (or key of the next member),
+    // their end, and whether they are objects; sized once from the
+    // document's deepest nesting (for a subtree an upper bound)
+    struct frame
+    {
+        const node* pos;
+        const node* end;
+        bool object;
+    };
 
     BasicJsonType result;
     sax_t sax(result, true);
     const string_t no_token{};
-    // the ends of the open containers, and whether they are objects; sized
-    // once from the document's deepest nesting (for a subtree an upper bound)
-    struct open_container
-    {
-        const node* end;
-        bool is_object;
-    };
-    std::vector<open_container> open((std::max)(d.max_depth, std::size_t{1}));
+    std::vector<frame> open((std::max)(d.max_depth, std::size_t{1}));
     std::size_t depth = 0;
     for (;;)
     {
+        // false positive: n comes from nav::value(), which never returns null for a valid index
+        // @infer-ignore NULLPTR_DEREFERENCE
         switch (static_cast<value_t>(n->kind))
         {
             case value_t::object:
@@ -72,69 +78,68 @@ BasicJsonType materialize(const document_data& d, const node* n)
                 }
                 if (NLOHMANN_VIEW_UNLIKELY(depth == open.size()))
                 {
-                    open.resize(depth * 2); // (deeper than the document's recorded nesting)
+                    open.resize(depth * 2); // (deeper than the recorded nesting, e.g. after edits)
                 }
-                open[depth++] = open_container{document_data::child_end(n), object};
-                n = document_data::first_child(n);
+                open[depth++] = frame{nav::first(d, n), nav::end(d, n), object};
                 break;
             }
             case value_t::string:
             {
                 string_t s(d.str(*n), n->len);
                 sax.string(s);
-                ++n;
                 break;
             }
             case value_t::number_integer:
                 sax.number_integer(static_cast<typename BasicJsonType::number_integer_t>(static_cast<std::int64_t>(integer_bits(*n))));
-                ++n;
                 break;
             case value_t::number_unsigned:
                 sax.number_unsigned(static_cast<typename BasicJsonType::number_unsigned_t>(integer_bits(*n)));
-                ++n;
                 break;
             case value_t::number_float:
                 sax.number_float(float_value<typename BasicJsonType::number_float_t>(d, *n), no_token);
-                ++n;
                 break;
             case value_t::boolean:
                 sax.boolean((n->flags & node_flags::is_true) != 0);
-                ++n;
                 break;
             case value_t::null:
             case value_t::binary:
             case value_t::discarded:
             default:
                 sax.null();
-                ++n;
                 break;
         }
+
+        // the next value: close finished containers, then read the key
         for (;;)
         {
             if (depth == 0)
             {
                 return result;
             }
-            if (n != open[depth - 1].end)
+            frame& f = open[depth - 1];
+            if (f.pos == f.end)
             {
-                break;
+                if (f.object)
+                {
+                    sax.end_object();
+                }
+                else
+                {
+                    sax.end_array();
+                }
+                --depth;
+                continue;
             }
-            if (open[depth - 1].is_object)
+            const node* entry = f.pos;
+            if (f.object)
             {
-                sax.end_object();
+                string_t key(d.str(*entry), entry->len);
+                sax.key(key);
+                ++entry;
             }
-            else
-            {
-                sax.end_array();
-            }
-            --depth;
-        }
-        if (open[depth - 1].is_object)
-        {
-            // the key of the next member
-            string_t key(d.str(*n), n->len);
-            sax.key(key);
-            ++n;
+            n = nav::value(entry);
+            f.pos = document_data::after(entry);
+            break;
         }
     }
 }

include/nlohmann/detail/view/node.hpp

@@ -33,20 +33,28 @@ constexpr std::size_t max_input_size() noexcept
 struct node_flags
 {
     static constexpr std::uint8_t escaped = 1; ///< string payload lives in the decode arena, not the source
+    static constexpr std::uint8_t edited = 2;  ///< string or number token lives in the edit arena (editable documents)
     static constexpr std::uint8_t storage = 3; ///< mask: where a string or number token lives (index into document_data::base)
     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
+/// elsewhere (the address of the value's node is kept in the len/next bytes)
+constexpr std::uint8_t kind_link = 10;
+
 /// One entry of the flat index, in document order. An object's members are
 /// stored as key node followed by the value's subtree. Integers keep their
 /// converted 64-bit value in the len/next bytes (the node after a scalar is
 /// always the next one, and the token length follows from `extra`).
 struct node
 {
-    std::uint8_t kind;   ///< value_t
+    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 object's key hash index (1-based, 0 = none); otherwise 0
-    std::uint32_t off;   ///< source offset (string content, number token, literal, bracket); arena offset if node_flags::escaped
+    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)
 };
@@ -65,6 +73,23 @@ NLOHMANN_VIEW_ALWAYS_INLINE bool is_container(const node& n) noexcept
     return static_cast<unsigned>(n.kind) - 1u <= 1u;
 }
 
+/// the value a link node stands for
+NLOHMANN_VIEW_ALWAYS_INLINE const node* link_target(const node& n) noexcept
+{
+    const node* t = nullptr;
+    std::memcpy(static_cast<void*>(&t), reinterpret_cast<const unsigned char*>(&n) + 8, sizeof(const node*)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    return t;
+}
+
+/// 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: 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

include/nlohmann/detail/view/number.hpp

@@ -10,6 +10,7 @@
 
 #include <cstddef> // size_t
 #include <cstdint> // int64_t, uint64_t
+#include <limits> // numeric_limits
 #include <string> // string
 #include <type_traits> // integral_constant
 
@@ -25,43 +26,76 @@ namespace detail
 namespace view
 {
 
+/*!
+@brief locate the decimal point and the end of the mantissa of a float token
+
+Also checks that the token is a JSON number. Tokens of the parser and of edits
+always are; an image loaded with image_check::bounds can hold any bytes, which
+must not reach the conversion (it expects a well-formed token).
+*/
+inline bool float_token_layout(const char* first, const char* last, std::size_t& dot, std::size_t& mantissa_end) noexcept
+{
+    const auto digit = [last](const char* q)
+    {
+        return q != last && is_digit(static_cast<unsigned char>(*q));
+    };
+    const char* p = first;
+    p += (p != last && *p == '-') ? 1 : 0;
+    if (!digit(p) || (*p == '0' && digit(p + 1)))
+    {
+        return false;
+    }
+    while (digit(p))
+    {
+        ++p;
+    }
+    dot = std::string::npos;
+    if (p != last && *p == '.')
+    {
+        dot = static_cast<std::size_t>(p - first);
+        if (!digit(++p))
+        {
+            return false;
+        }
+        while (digit(p))
+        {
+            ++p;
+        }
+    }
+    mantissa_end = static_cast<std::size_t>(p - first);
+    if (p != last && (*p == 'e' || *p == 'E'))
+    {
+        ++p;
+        p += (p != last && (*p == '+' || *p == '-')) ? 1 : 0;
+        if (!digit(p))
+        {
+            return false;
+        }
+        while (digit(p))
+        {
+            ++p;
+        }
+    }
+    return p == last;
+}
+
 /*!
 @brief the value of the float token of a node, as parse() converts it
 
 Uses the lexer's conversion (detail::convert_float), so that the values are
 bit-identical to parse(): float and double are converted without allocation
-and independent of the locale. The digit layout recorded while parsing locates
-the decimal point and the exponent without scanning the token.
+and independent of the locale. A token that is not a JSON number (only in a
+damaged image loaded with image_check::bounds) yields 0.
 */
 template<typename FloatType>
 NLOHMANN_VIEW_NOINLINE FloatType float_value(const char* first, const node& n)
 {
     const char* const last = first + n.len;
-    const std::size_t neg = first[0] == '-' ? 1 : 0;
-    const std::size_t int_digits = n.extra & 0xFFu;
-    const std::size_t frac_digits = n.extra >> 8u;
-    std::size_t dot = std::string::npos;
-    std::size_t mantissa_end = n.len;
-    if (int_digits != 255 && frac_digits != 255)
+    std::size_t dot = 0;
+    std::size_t mantissa_end = 0;
+    if (NLOHMANN_VIEW_UNLIKELY(!float_token_layout(first, last, dot, mantissa_end)))
     {
-        dot = frac_digits != 0 ? neg + int_digits : std::string::npos;
-        mantissa_end = neg + int_digits + (frac_digits != 0 ? 1 + frac_digits : 0);
-    }
-    else
-    {
-        // more digits than the layout records: locate them
-        for (std::size_t i = 0; i < n.len; ++i)
-        {
-            if (first[i] == '.')
-            {
-                dot = i;
-            }
-            else if (first[i] == 'e' || first[i] == 'E')
-            {
-                mantissa_end = i;
-                break;
-            }
-        }
+        return FloatType{};
     }
     return convert_float<FloatType>(first, last, dot, mantissa_end);
 }
@@ -92,16 +126,20 @@ NLOHMANN_VIEW_ALWAYS_INLINE float_significand layout_decimal(const unsigned char
     }
     if (p != e)
     {
-        // [eE][+-]digits; huge exponents saturate (the parser rejected overflow)
+        // [eE][+-]digits; huge exponents saturate (the parser rejected
+        // overflow). The token is not read beyond e, and the digits are taken
+        // as unsigned, so that a token that is not well-formed (a damaged
+        // image loaded with image_check::bounds) yields a wrong value, but no
+        // overflow.
         ++p;
-        const bool exp_negative = *p == '-';
-        p += (*p == '-' || *p == '+') ? 1 : 0;
+        const bool exp_negative = p != e && *p == '-';
+        p += (p != e && (*p == '-' || *p == '+')) ? 1 : 0;
         std::int64_t exp_value = 0;
         for (; p != e; ++p)
         {
             if (exp_value < 0x10000000)
             {
-                exp_value = (exp_value * 10) + (*p - '0');
+                exp_value = (exp_value * 10) + static_cast<unsigned char>(*p - '0');
             }
         }
         q += exp_negative ? -exp_value : exp_value;
@@ -128,11 +166,31 @@ NLOHMANN_VIEW_ALWAYS_INLINE FloatType layout_float(const unsigned char* p, const
     return decimal_to_float<FloatType>(layout_decimal(p, e, int_digits, frac_digits, limit));
 }
 
+/// the value of a float set by an edit: its token (the shortest round-trip
+/// text, or "nan", "inf", "-inf") in the edit arena
+template<typename FloatType>
+NLOHMANN_VIEW_NOINLINE FloatType edited_float(const char* token, const node& n)
+{
+    if (token[0] == 'n')
+    {
+        return std::numeric_limits<FloatType>::quiet_NaN();
+    }
+    if (token[0] == 'i' || (token[0] == '-' && token[1] == 'i'))
+    {
+        return token[0] == 'i' ? std::numeric_limits<FloatType>::infinity() : -std::numeric_limits<FloatType>::infinity();
+    }
+    return float_value<FloatType>(token, n);
+}
+
 /// the value of the float token of a node, as parse() converts it; floats and
 /// doubles with at most 19 digits are converted from the digit layout
 template<typename FloatType>
 FloatType float_value(const document_data& d, const node& n)
 {
+    if (NLOHMANN_VIEW_UNLIKELY((n.flags & node_flags::storage) == node_flags::edited))
+    {
+        return edited_float<FloatType>(d.str(n), n);
+    }
     return float_value<FloatType>(d, n, std::integral_constant<bool, has_native_float_format<FloatType>::value> {});
 }
 

include/nlohmann/detail/view/object_index.hpp

@@ -13,7 +13,6 @@
 #include <cstring> // memcmp
 
 #include <nlohmann/json.hpp>
-#include <nlohmann/detail/meta/type_traits.hpp>
 #include <nlohmann/detail/view/document_data.hpp>
 #include <nlohmann/detail/view/macro_scope.hpp>
 #include <nlohmann/detail/view/node.hpp>

include/nlohmann/detail/view/serializer.hpp

@@ -31,7 +31,11 @@ namespace view
 {
 
 /// append-only output buffer: writes through a raw pointer into a string that
-/// is resized ahead, and trimmed by finish()
+/// is resized ahead, and trimmed by finish(). The estimate is reserved, and the
+/// string grows in steps of 64 KiB within it: resize() fills the new bytes
+/// with zeros (before C++23, a string cannot grow without), and a small step
+/// is filled while the writer is about to use it, in the cache, instead of
+/// filling the whole estimate in memory first.
 template<typename StringType>
 class output_buffer
 {
@@ -83,17 +87,49 @@ class output_buffer
         m_pos += n;
     }
 
+    /// the write position and the end of the writable space, for a writer
+    /// that keeps the position in a local variable (set_cursor() hands it back)
+    char* cursor() const noexcept
+    {
+        return m_pos;
+    }
+
+    char* limit() const noexcept
+    {
+        return m_end;
+    }
+
+    void set_cursor(char* p) noexcept
+    {
+        m_pos = p;
+    }
+
   private:
+    /// the size of a growth step (a function: std::min() takes a reference,
+    /// which a static constexpr member does not have before C++17)
+    static constexpr std::size_t step() noexcept
+    {
+        return 65536;
+    }
+
     static StringType& sized(StringType& out, std::size_t estimate)
     {
-        out.resize((std::max)(estimate, static_cast<std::size_t>(64)));
+        out.reserve(estimate);
+        out.resize((std::min)((std::max)(estimate, static_cast<std::size_t>(64)), step()));
         return out;
     }
 
     NLOHMANN_VIEW_NOINLINE void grow(std::size_t n)
     {
         const auto used = static_cast<std::size_t>(m_pos - m_out.data());
-        m_out.resize((std::max)(m_out.size() * 2, used + n + 256));
+        // (a step does not go beyond the reserved estimate, so that a good
+        // estimate is never copied to a larger allocation)
+        const std::size_t size = (std::max)((std::min)(m_out.size() + step(), m_out.capacity()), used + n + 256);
+        if (size > m_out.capacity())
+        {
+            m_out.reserve((std::max)(m_out.capacity() * 2, size));
+        }
+        m_out.resize(size);
         m_pos = &m_out[0] + used;
         m_end = &m_out[0] + m_out.size();
     }
@@ -103,6 +139,105 @@ class output_buffer
     char* m_end;
 };
 
+/// The length of the run at s that dump() writes unchanged without
+/// ensure_ascii: all bytes but quotes, backslashes, and control characters.
+/// Unlike detail::string_bulk_run(), non-ASCII bytes are not validated: the
+/// strings of a document are valid UTF-8 (a damaged image loaded with
+/// image_check::bounds can have others, which are then written unchanged).
+inline std::size_t plain_output_run(const unsigned char* s, std::size_t n) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        const std::uint64_t v = read_eight_bytes(s + i);
+        const std::uint64_t q = v ^ 0x2222222222222222ull; // '"'
+        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull; // '\\'
+        const std::uint64_t stop = (((q - ones) & ~q) | ((b - ones) & ~b) | ((v - 0x2020202020202020ull) & ~v)) & high;
+        if (stop != 0)
+        {
+            // the lowest flagged byte is the first stop: borrows only flag bytes above a true one
+            return i + (static_cast<std::size_t>(count_trailing_zeros(stop)) / 8);
+        }
+    }
+    for (; i < n; ++i)
+    {
+        if (s[i] == '"' || s[i] == '\\' || s[i] < 0x20)
+        {
+            return i;
+        }
+    }
+    return n;
+}
+
+/// A stack that starts in a buffer of the caller (a local array) and moves to
+/// the heap (a vector of the caller) only when that is full, so that dumps of
+/// shallow documents need no allocation. The top is a pointer, as in
+/// std::vector. The address of the stack never escapes (the growth gets the
+/// vector and returns the new storage), so its pointers stay in registers.
+template<typename T>
+class small_stack
+{
+  public:
+    small_stack(T* buffer, std::size_t capacity, std::vector<T>& heap) noexcept
+        : m_begin(buffer), m_top(buffer), m_end(buffer + capacity), m_heap(&heap)
+    {}
+    small_stack(const small_stack&) = delete;
+    small_stack(small_stack&&) = delete;
+    small_stack& operator=(const small_stack&) = delete;
+    small_stack& operator=(small_stack&&) = delete;
+    ~small_stack() = default;
+
+    NLOHMANN_VIEW_ALWAYS_INLINE void push_back(const T& x)
+    {
+        if (NLOHMANN_VIEW_UNLIKELY(m_top == m_end))
+        {
+            const std::size_t used = size();
+            const std::size_t capacity = 2 * static_cast<std::size_t>(m_end - m_begin);
+            m_begin = grow(*m_heap, m_begin, used, capacity);
+            m_top = m_begin + used;
+            m_end = m_begin + capacity;
+        }
+        *m_top++ = x;
+    }
+
+    NLOHMANN_VIEW_ALWAYS_INLINE T& back() noexcept
+    {
+        return m_top[-1];
+    }
+
+    NLOHMANN_VIEW_ALWAYS_INLINE void pop_back() noexcept
+    {
+        --m_top;
+    }
+
+    NLOHMANN_VIEW_ALWAYS_INLINE bool empty() const noexcept
+    {
+        return m_top == m_begin;
+    }
+
+    NLOHMANN_VIEW_ALWAYS_INLINE std::size_t size() const noexcept
+    {
+        return static_cast<std::size_t>(m_top - m_begin);
+    }
+
+  private:
+    /// the used entries moved to heap storage of the given capacity
+    NLOHMANN_VIEW_NOINLINE static T* grow(std::vector<T>& heap, const T* begin, std::size_t used, std::size_t capacity)
+    {
+        std::vector<T> bigger(capacity);
+        std::copy(begin, begin + used, bigger.begin());
+        heap.swap(bigger);
+        return heap.data();
+    }
+
+    T* m_begin;
+    T* m_top;
+    T* m_end;
+    std::vector<T>* m_heap;
+};
+
 /// how the view's dump() writes a value
 struct dump_style
 {
@@ -123,11 +258,14 @@ the library's conversion; integers are copied from the source, where they
 are canonical (except "-0", which parse() reads as 0). The walk is
 iterative, so the nesting depth is limited by memory only.
 */
-template<typename BasicJsonType>
+template<typename BasicJsonType, bool Editable>
 class view_serializer
 {
+    using nav = navigation<Editable>;
     using string_t = typename BasicJsonType::string_t;
     using number_float_t = typename BasicJsonType::number_float_t;
+    /// doubles that are IEEE 754 binary64 are written from their bits (Zmij)
+    using fast_double = std::integral_constant < bool, std::is_same<number_float_t, double>::value && ::nlohmann::detail::dtoa_impl::is_binary64<double>::value >;
 
   public:
     view_serializer(const document_data& d, string_t& out, std::size_t estimate, const dump_style& style)
@@ -136,6 +274,18 @@ class view_serializer
 
     void dump(const node* root)
     {
+        if (!m_style.pretty && !m_style.ensure_ascii)
+        {
+            if (m_style.source_numbers)
+            {
+                dump_compact<true>(root);
+            }
+            else
+            {
+                dump_compact<false>(root);
+            }
+            return;
+        }
         struct frame
         {
             const node* pos; ///< next element, or key of the next member
@@ -143,7 +293,9 @@ class view_serializer
             bool object;
             bool first;  ///< nothing written yet
         };
-        std::vector<frame> stack;
+        std::array<frame, 32> buffer; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::vector<frame> heap;
+        small_stack<frame> stack(buffer.data(), buffer.size(), heap);
         const node* n = root;
         for (;;)
         {
@@ -158,7 +310,7 @@ class view_serializer
                 else
                 {
                     m_out.put(object ? '{' : '[');
-                    stack.push_back(frame{document_data::first_child(n), document_data::child_end(n), object, true});
+                    stack.push_back(frame{nav::first(m_doc, n), nav::end(m_doc, n), object, true});
                 }
             }
             else
@@ -200,19 +352,313 @@ class view_serializer
                     {
                         m_out.put(':');
                     }
-                    n = f.pos + 1;
+                    n = nav::value(f.pos + 1);
+                    f.pos = document_data::after(f.pos + 1);
                 }
                 else
                 {
-                    n = f.pos;
+                    n = nav::value(f.pos);
+                    f.pos = document_data::after(f.pos);
                 }
-                f.pos = document_data::after(n);
                 break;
             }
         }
     }
 
   private:
+    /// a string that is not a plain string of the source (decoded, or written
+    /// by an edit), without ensure_ascii: runs without characters to escape
+    /// are copied
+    NLOHMANN_VIEW_NOINLINE void write_decoded(const node& n)
+    {
+        const auto* const s = reinterpret_cast<const unsigned char*>(m_doc.str(n)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+        m_out.put('"');
+        for (std::size_t i = 0; i < n.len;)
+        {
+            const std::size_t run = plain_output_run(s + i, n.len - i);
+            if (run != 0)
+            {
+                m_out.put(reinterpret_cast<const char*>(s + i), run); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+                i += run;
+                continue;
+            }
+            write_codepoint<false>(s[i], s + i, 1); // a quote, a backslash, or a control character
+            ++i;
+        }
+        m_out.put('"');
+    }
+
+    /// the copies of dump_compact() that are not fixed-size moves (long
+    /// strings, or near the end of the source); out of line, so that the
+    /// compiler does not merge the fixed-size moves into this call
+    NLOHMANN_VIEW_NOINLINE static void copy_long(char* to, const char* from, std::size_t n) noexcept
+    {
+        std::memcpy(to, from, n);
+    }
+
+    /// a compile-time option as a runtime condition: testing the template
+    /// argument directly makes a condition like `Editable && c` constant when
+    /// the option is off, which MSVC reports as C4127
+    static NLOHMANN_VIEW_ALWAYS_INLINE bool enabled(bool option) noexcept
+    {
+        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)
+    {
+        struct frame
+        {
+            const node* pos; ///< (editable documents) next element, or key of the next member
+            const node* end;
+            bool object;
+        };
+        std::array<frame, 32> buffer; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::vector<frame> heap;
+        small_stack<frame> stack(buffer.data(), buffer.size(), heap);
+        const char* const src = m_doc.src;
+        const char* const src_end = src + m_doc.size;
+        char* w = m_out.cursor();
+        char* lim = m_out.limit();
+        // room for n bytes and the slack
+        const auto room = [&](std::size_t n)
+        {
+            if (NLOHMANN_VIEW_UNLIKELY(static_cast<std::size_t>(lim - w) < n + 64))
+            {
+                m_out.set_cursor(w);
+                m_out.reserve(n + 64);
+                w = m_out.cursor();
+                lim = m_out.limit();
+            }
+        };
+        // copy n bytes of the source (after room(n))
+        const auto copy = [&](const char* from, std::size_t n)
+        {
+            if (n <= 32 && static_cast<std::size_t>(src_end - from) >= 32)
+            {
+                std::memcpy(w, from, 32);
+            }
+            else if (n <= 256 && static_cast<std::size_t>(src_end - from) >= n + 32)
+            {
+                for (std::size_t i = 0; i < n; i += 32)
+                {
+                    std::memcpy(w + i, from + i, 32);
+                }
+            }
+            else
+            {
+                copy_long(w, from, n);
+            }
+            w += n;
+        };
+        // a literal of n bytes (after room(n))
+        const auto literal = [&](const char* text, std::size_t n)
+        {
+            std::memcpy(w, text, n);
+            w += n;
+        };
+        // a string that is not a plain string of the source (out of line, so
+        // that the cursor stays in a register here)
+        const auto escaped = [&](const node & n)
+        {
+            m_out.set_cursor(w);
+            write_decoded(n);
+            w = m_out.cursor();
+            lim = m_out.limit();
+        };
+
+        // Read-only documents: the elements of a container follow it in the
+        // node array, so the walk goes through the array in order, and a
+        // frame only needs the end of its container. Editable documents: the
+        // elements of a moved container live elsewhere, so a frame keeps the
+        // position of the next element (see navigation).
+        // The innermost open container is kept in registers (cur; end ==
+        // nullptr: none), the stack holds the ones around it.
+        frame cur{nullptr, nullptr, false};
+        const node* n = root;
+        for (;;)
+        {
+            // write the value at n (read-only documents: and advance n)
+            bool opened = false;
+            // false positive: n comes from nav::value(), which never returns null for a valid index
+            // @infer-ignore NULLPTR_DEREFERENCE
+            switch (static_cast<value_t>(n->kind))
+            {
+                case value_t::string:
+                    if ((n->flags & node_flags::storage) == 0)
+                    {
+                        room(n->len + 2);
+                        *w++ = '"';
+                        copy(src + n->off, n->len);
+                        *w++ = '"';
+                    }
+                    else
+                    {
+                        escaped(*n);
+                    }
+                    break;
+                case value_t::number_integer:
+                case value_t::number_unsigned:
+                {
+                    const std::uint32_t len = number_length(*n);
+                    room(len);
+                    if (enabled(Editable) && (n->flags & node_flags::storage) != 0)
+                    {
+                        copy_long(w, m_doc.str(*n), len); // a canonical token written by an edit
+                        w += len;
+                        break;
+                    }
+                    const char* const token = src + n->off;
+                    if (!enabled(SourceNumbers) && NLOHMANN_VIEW_UNLIKELY(len == 2 && token[0] == '-' && token[1] == '0'))
+                    {
+                        *w++ = '0'; // parse() reads -0 as the integer 0
+                    }
+                    else
+                    {
+                        copy(token, len);
+                    }
+                    break;
+                }
+                case value_t::number_float:
+                    if (enabled(SourceNumbers) && (n->flags & node_flags::storage) != node_flags::edited)
+                    {
+                        room(n->len);
+                        copy(src + n->off, n->len);
+                    }
+                    else if (enabled(fast_double::value))
+                    {
+                        room(64);
+                        w = write_double_at(w, *n);
+                    }
+                    else
+                    {
+                        m_out.set_cursor(w);
+                        write_float_node(*n);
+                        w = m_out.cursor();
+                        lim = m_out.limit();
+                    }
+                    break;
+                case value_t::boolean:
+                    room(8);
+                    if ((n->flags & node_flags::is_true) != 0)
+                    {
+                        literal("true", 4);
+                    }
+                    else
+                    {
+                        literal("false", 5);
+                    }
+                    break;
+                case value_t::object:
+                case value_t::array:
+                {
+                    const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
+                    room(8);
+                    if (n->len == 0)
+                    {
+                        literal(object ? "{}" : "[]", 2);
+                    }
+                    else
+                    {
+                        *w++ = object ? '{' : '[';
+                        stack.push_back(cur);
+                        if (Editable)
+                        {
+                            cur = frame{nav::first(m_doc, n), nav::end(m_doc, n), object};
+                        }
+                        else
+                        {
+                            cur = frame{nullptr, n + n->next, object};
+                        }
+                        opened = true;
+                    }
+                    break;
+                }
+                case value_t::null:
+                    room(8);
+                    literal("null", 4);
+                    break;
+                case value_t::binary:    // LCOV_EXCL_LINE (not in a document)
+                case value_t::discarded: // LCOV_EXCL_LINE
+                default:                 // LCOV_EXCL_LINE
+                    break;               // LCOV_EXCL_LINE
+            }
+            if (!Editable)
+            {
+                ++n; // the next node: the first element of an opened container, or the node after a scalar
+            }
+
+            // go to the next value: close finished containers, then separate
+            // (a container just opened has an element)
+            if (!opened)
+            {
+                for (;;)
+                {
+                    if (cur.end == nullptr)
+                    {
+                        m_out.set_cursor(w);
+                        m_out.finish();
+                        return;
+                    }
+                    if ((Editable ? cur.pos : n) != cur.end)
+                    {
+                        break;
+                    }
+                    room(1);
+                    *w++ = cur.object ? '}' : ']';
+                    cur = stack.back();
+                    stack.pop_back();
+                }
+                room(1);
+                *w++ = ',';
+            }
+            const node* const at = Editable ? cur.pos : n;
+            if (cur.object)
+            {
+                const node& key = *at;
+                if ((key.flags & node_flags::storage) == 0)
+                {
+                    room(key.len + 3);
+                    *w++ = '"';
+                    copy(src + key.off, key.len);
+                    w[0] = '"';
+                    w[1] = ':';
+                    w += 2;
+                }
+                else
+                {
+                    escaped(key);
+                    room(1);
+                    *w++ = ':';
+                }
+                if (Editable)
+                {
+                    n = nav::value(at + 1);
+                    cur.pos = document_data::after(at + 1);
+                }
+                else
+                {
+                    ++n;
+                }
+            }
+            else if (Editable)
+            {
+                n = nav::value(at);
+                cur.pos = document_data::after(at);
+            }
+        }
+    }
+
     void newline(std::size_t level)
     {
         if (m_style.pretty)
@@ -258,13 +704,13 @@ class view_serializer
                 break;
             }
             case value_t::number_float:
-                if (m_style.source_numbers)
+                if (m_style.source_numbers && (n.flags & node_flags::storage) != node_flags::edited)
                 {
-                    m_out.put(m_doc.str(n), n.len);
+                    m_out.put(m_doc.str(n), n.len); // (a float set by an edit is written as with shortest)
                 }
                 else
                 {
-                    write_float(float_value<number_float_t>(m_doc, n));
+                    write_float_node(n);
                 }
                 break;
             case value_t::object:    // LCOV_EXCL_LINE (containers are written by dump())
@@ -276,6 +722,88 @@ class view_serializer
         }
     }
 
+    /// a float node as dump() writes it
+    void write_float_node(const node& n)
+    {
+        write_float_node(n, fast_double {});
+    }
+
+    void write_float_node(const node& n, std::false_type /*other*/)
+    {
+        write_float(float_value<number_float_t>(m_doc, n));
+    }
+
+    void write_float_node(const node& n, std::true_type /*double*/)
+    {
+        m_out.reserve(64);
+        m_out.set_cursor(write_double_at(m_out.cursor(), n));
+    }
+
+    /*!
+    @brief (doubles) the float at n as dump() writes it, at w (64 bytes of room)
+
+    A token of at most 15 significant digits is written from its digits,
+    without a conversion: two decimals of at most 15 digits are farther
+    apart than the rounding interval of a (normal) double (the argument
+    behind DBL_DIG), so the token's digits are the shortest ones of its
+    double, which the library's conversion writes (Zmij). Other tokens are
+    converted from the digits already read.
+    */
+    char* write_double_at(char* w, const node& n)
+    {
+        const unsigned int_digits = n.extra & 0xFFu;
+        const unsigned frac_digits = n.extra >> 8u;
+        if ((n.flags & node_flags::storage) != node_flags::edited && int_digits + frac_digits <= 19)
+        {
+            const auto* const first = reinterpret_cast<const unsigned char*>(m_doc.src + n.off); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+            const float_significand d = layout_decimal(first, first + n.len, int_digits, frac_digits, reinterpret_cast<const unsigned char*>(m_doc.src + m_doc.size)); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+            // (the exponent keeps the value far from subnormals and overflow)
+            if (d.w != 0 && d.w < 1000000000000000u && d.exponent >= -290 && d.exponent <= 290)
+            {
+                *w = '-';
+                w += d.negative ? 1 : 0;
+                // (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)
+        }
+        return write_double_value_at(w, static_cast<double>(float_value<number_float_t>(m_doc, n)));
+    }
+
+    /// n bytes of text at w
+    static char* write_text_at(char* w, const char* text, std::size_t n) noexcept
+    {
+        std::memcpy(w, text, n);
+        return w + n;
+    }
+
+    /// a double as dump() writes it, at w (64 bytes of room)
+    static char* write_double_value_at(char* w, double x)
+    {
+        // (from the bits: without the checks of to_chars())
+        std::uint64_t bits = 0;
+        std::memcpy(&bits, &x, sizeof(bits));
+        if (NLOHMANN_VIEW_UNLIKELY((bits & 0x7FF0000000000000u) == 0x7FF0000000000000u))
+        {
+            return write_text_at(w, "null", 4);
+        }
+        *w = '-';
+        w += bits >> 63u;
+        bits &= ~(std::uint64_t{1} << 63u);
+        if (bits == 0)
+        {
+            return write_text_at(w, "0.0", 3);
+        }
+        return ::nlohmann::detail::dtoa_impl::write_shortest(w, ::nlohmann::detail::zmij::to_shortest(bits));
+    }
+
     /// as serializer::dump_float()
     void write_float(number_float_t x)
     {
@@ -309,9 +837,9 @@ class view_serializer
     {
         const char* const s = m_doc.str(n);
         m_out.put('"');
-        if ((n.flags & node_flags::escaped) == 0 && !m_style.ensure_ascii)
+        if ((n.flags & node_flags::storage) == 0 && !m_style.ensure_ascii)
         {
-            // a string without escape sequences has nothing to escape
+            // a string of the source without escape sequences has nothing to escape
             m_out.put(s, n.len);
         }
         else if (m_style.ensure_ascii)
@@ -325,7 +853,9 @@ class view_serializer
         m_out.put('"');
     }
 
-    /// as serializer::dump_escaped() for valid UTF-8 (the view has no other)
+    /// as serializer::dump_escaped(); strings of a document are valid UTF-8,
+    /// except in a damaged image loaded with image_check::bounds, for which
+    /// this throws what basic_json::dump() throws for the string
     template<bool EnsureAscii>
     void write_escaped(const unsigned char* s, std::size_t n)
     {
@@ -349,12 +879,13 @@ class view_serializer
             }
             std::uint32_t codepoint = s[i];
             std::size_t len = 1;
-            if (codepoint >= 0xC0)
+            if (codepoint >= 0x80)
             {
-                len = 2;
-                if (codepoint >= 0xE0)
+                len = validate_one_utf8(s + i, n - i);
+                if (NLOHMANN_VIEW_UNLIKELY(len == 0))
                 {
-                    len = codepoint >= 0xF0 ? 4 : 3;
+                    invalid_utf8(s, n);
+                    return;
                 }
                 codepoint &= 0xFFu >> (len + 1);
                 for (std::size_t k = 1; k < len; ++k)
@@ -367,6 +898,13 @@ class view_serializer
         }
     }
 
+    /// throw what basic_json::dump() throws for a string that is not valid UTF-8
+    NLOHMANN_VIEW_NOINLINE static void invalid_utf8(const unsigned char* s, std::size_t n)
+    {
+        const string_t dumped = BasicJsonType(string_t(reinterpret_cast<const char*>(s), n)).dump(); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+        static_cast<void>(dumped);
+    }
+
     template<bool EnsureAscii>
     void write_codepoint(std::uint32_t codepoint, const unsigned char* bytes, std::size_t len)
     {

include/nlohmann/json_view.hpp

@@ -7,14 +7,16 @@
 // 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      *
  * containers, C strings); rvalue strings, streams, and other inputs are     *
@@ -24,10 +26,10 @@
 #ifndef INCLUDE_NLOHMANN_JSON_VIEW_HPP_
 #define INCLUDE_NLOHMANN_JSON_VIEW_HPP_
 
-#include <algorithm> // min
+#include <algorithm> // all_of, min
 #include <array> // array
 #include <cstddef> // nullptr_t, size_t // IWYU pragma: keep
-#include <cstdint> // uint32_t
+#include <cstdint> // uint8_t, uint32_t
 #include <cstring> // memcpy, strlen
 #include <istream> // istream // IWYU pragma: keep
 #include <iterator> // distance, input_iterator_tag, iterator_traits
@@ -67,7 +69,9 @@
 #include <nlohmann/detail/view/builder.hpp>
 #include <nlohmann/detail/view/compare.hpp>
 #include <nlohmann/detail/view/document_data.hpp>
+#include <nlohmann/detail/view/edit.hpp>
 #include <nlohmann/detail/view/errors.hpp>
+#include <nlohmann/detail/view/image.hpp>
 #include <nlohmann/detail/view/input.hpp>
 #include <nlohmann/detail/view/iterator.hpp>
 #include <nlohmann/detail/view/lookup.hpp>
@@ -88,11 +92,13 @@ NLOHMANN_JSON_NAMESPACE_BEGIN
 Trivially copyable (two pointers). Valid as long as the document is alive and
 has not been re-parsed, and as long as a borrowed source text is alive.
 */
-template<typename BasicJsonType>
+template<typename BasicJsonType, bool Editable = false>
 class basic_json_view
 {
     using node = detail::view::node;
     using document_data = detail::view::document_data;
+    /// how the index is walked (with edits only for editable documents)
+    using navigation = detail::view::navigation<Editable>;
 
   public:
     using value_t = detail::value_t;
@@ -289,7 +295,7 @@ class 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, detail::view::element_at(m_node, idx)) : basic_json_view();
+        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();
     }
 
     /// any other integer type (int, unsigned, long, std::int64_t, ...; a
@@ -352,7 +358,7 @@ class basic_json_view
         {
             detail::view::throw_out_of_range(401, detail::concat("array index ", std::to_string(idx), " is out of range"));
         }
-        return basic_json_view(m_doc, detail::view::element_at(m_node, idx));
+        return basic_json_view(m_doc, navigation::value(detail::view::element_at<Editable>(*m_doc, m_node, idx)));
     }
 
     /// any other integer type, see operator[]; negative values are out of
@@ -427,7 +433,7 @@ class basic_json_view
     {
         if (is_structured() && m_node->len != 0)
         {
-            return basic_json_view(m_doc, detail::view::last_child(m_node) + (is_object() ? 1 : 0));
+            return basic_json_view(m_doc, navigation::value(detail::view::last_child<Editable>(*m_doc, m_node) + (is_object() ? 1 : 0)));
         }
         return front();
     }
@@ -444,7 +450,7 @@ class basic_json_view
         {
             return end();
         }
-        const node* const k = detail::view::find_member(*m_doc, m_node, key.data(), key.size());
+        const node* const k = detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size());
         return k != nullptr ? iterator(m_doc, k, true) : end();
     }
 
@@ -461,7 +467,7 @@ class basic_json_view
     /// whether this is an object with a member with this key
     bool contains(string_view_t key) const
     {
-        return is_object() && detail::view::find_member(*m_doc, m_node, key.data(), key.size()) != nullptr;
+        return is_object() && detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size()) != nullptr;
     }
 
     bool contains(const char* key) const
@@ -485,7 +491,7 @@ class basic_json_view
     /// more than once); 0 if this is not an object
     size_type count(string_view_t key) const
     {
-        return is_object() ? detail::view::count_members(*m_doc, m_node, key.data(), key.size()) : 0;
+        return is_object() ? detail::view::count_members<Editable>(*m_doc, m_node, key.data(), key.size()) : 0;
     }
 
     size_type count(const char* key) const
@@ -508,7 +514,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_LIKELY(is_structured()))
         {
-            return iterator(m_doc, document_data::first_child(m_node), is_object());
+            return iterator(m_doc, navigation::first(*m_doc, m_node), is_object());
         }
         return iterator(m_doc, m_node, false);
     }
@@ -517,7 +523,7 @@ class basic_json_view
     {
         if (NLOHMANN_VIEW_LIKELY(is_structured()))
         {
-            return iterator(m_doc, document_data::child_end(m_node), is_object());
+            return iterator(m_doc, navigation::end(*m_doc, m_node), is_object());
         }
         return iterator(m_doc, (is_null() || is_discarded()) ? m_node : m_node + 1, false);
     }
@@ -617,9 +623,11 @@ class basic_json_view
         style.indent_char = indent_char;
         style.ensure_ascii = ensure_ascii;
         style.source_numbers = numbers == number_format::source;
-        // the compact text is about as long as the source text of the value
-        const std::size_t estimate = source_extent() + (style.pretty ? source_extent() / 2 : 0) + 64;
-        detail::view::view_serializer<BasicJsonType>(*m_doc, out, estimate, style).dump(m_node);
+        // the compact text is about as long as the source text of the value;
+        // the compact writer keeps 64 bytes of slack, so that it does not grow
+        // the buffer just before the end
+        const std::size_t estimate = source_extent() + (style.pretty ? source_extent() / 2 : 0) + 160;
+        detail::view::view_serializer<BasicJsonType, Editable>(*m_doc, out, estimate, style).dump(m_node);
         return out;
     }
 
@@ -653,6 +661,19 @@ class basic_json_view
         return !(a == b);
     }
 
+    /// a view of an editable document compares with one of a read-only document
+    template < bool E, typename std::enable_if < E != Editable, int >::type = 0 >
+    friend bool operator==(const basic_json_view& a, const basic_json_view<BasicJsonType, E>& b)
+    {
+        return detail::view::equal<BasicJsonType>(side(a), detail::view::view_side<BasicJsonType, basic_json_view<BasicJsonType, E>>(b));
+    }
+
+    template < bool E, typename std::enable_if < E != Editable, int >::type = 0 >
+    friend bool operator!=(const basic_json_view& a, const basic_json_view<BasicJsonType, E>& b)
+    {
+        return !(a == b);
+    }
+
     /// whether the value parse() would produce for a view equals a value
     friend bool operator==(const basic_json_view& a, const BasicJsonType& j)
     {
@@ -686,7 +707,7 @@ class basic_json_view
         {
             return BasicJsonType(value_t::discarded);
         }
-        return detail::view::materialize<BasicJsonType>(*m_doc, m_node);
+        return detail::view::materialize<BasicJsonType, Editable>(*m_doc, m_node);
     }
 
     /// byte offset of this value in the source text (for strings: of the
@@ -694,12 +715,14 @@ class basic_json_view
     /// a discarded view and for strings with escapes, which are decoded
     std::size_t source_offset() const noexcept
     {
-        return m_node != nullptr && (m_node->flags & detail::view::node_flags::storage) == 0
+        return m_node != nullptr && (m_node->flags & (detail::view::node_flags::storage | detail::view::node_flags::moved | detail::view::node_flags::is_new)) == 0
                ? m_node->off : static_cast<std::size_t>(-1);
     }
 
   private:
-    template<typename> friend class basic_json_document;
+    template<typename, bool> friend class basic_json_document;
+    template<typename, bool> friend class basic_json_view;
+    template<typename, typename> friend class detail::view::editor;
     friend iterator;
 
     basic_json_view(const document_data* d, const node* n) noexcept
@@ -713,10 +736,23 @@ class basic_json_view
         return detail::view::view_side<BasicJsonType, basic_json_view>(v);
     }
 
+    /// the template argument as a runtime condition: testing it directly in
+    /// `Editable && ...` makes the condition constant, which MSVC reports as
+    /// C4127
+    static bool editable() noexcept
+    {
+        return Editable;
+    }
+
     /// the number of source bytes of this value (estimated for values with
     /// decoded strings); the estimate sizes the output buffer of dump()
     std::size_t source_extent() const noexcept
     {
+        if (editable() && m_doc->edits != nullptr)
+        {
+            // positions of moved and new values are not source offsets
+            return m_node == m_doc->nodes ? m_doc->size + m_doc->edits->text_used : 64;
+        }
         const node* const end = m_doc->nodes + m_doc->node_count;
         if ((m_node->flags & detail::view::node_flags::storage) != 0)
         {
@@ -747,8 +783,8 @@ class basic_json_view
     /// (object required)
     NLOHMANN_VIEW_ALWAYS_INLINE basic_json_view lookup(string_view_t key) const noexcept
     {
-        const node* const k = detail::view::find_member(*m_doc, m_node, key.data(), key.size());
-        return k != nullptr ? basic_json_view(m_doc, k + 1) : basic_json_view();
+        const node* const k = detail::view::find_member<Editable>(*m_doc, m_node, key.data(), key.size());
+        return k != nullptr ? basic_json_view(m_doc, navigation::value(k + 1)) : basic_json_view();
     }
 
     // --- get() dispatch ---
@@ -854,7 +890,7 @@ Borrowed parses keep a pointer to the caller's text, which must outlive the
 document. Owned parses (parse_copy, rvalue std::string, streams, and inputs
 that are not contiguous byte ranges) keep their own copy.
 */
-template<typename BasicJsonType>
+template<typename BasicJsonType, bool Editable = false>
 class basic_json_document
 {
     using document_data = detail::view::document_data;
@@ -863,7 +899,7 @@ class basic_json_document
                   "json_view supports 64-bit integer types only");
 
   public:
-    using view_type = basic_json_view<BasicJsonType>;
+    using view_type = basic_json_view<BasicJsonType, Editable>;
     using value_t = detail::value_t;
 
     /// an empty (discarded) document
@@ -993,7 +1029,7 @@ class basic_json_document
     /// whether the document holds its own copy of the text
     bool owns_source() const noexcept
     {
-        return m_data && !m_data->owned.empty() && m_data->src == m_data->owned.data();
+        return m_data && ((!m_data->owned.empty() && m_data->src == m_data->owned.data()) || !m_data->owned_image.empty());
     }
 
     /// number of index nodes (values plus object keys)
@@ -1002,7 +1038,7 @@ class basic_json_document
         return m_data ? m_data->node_count : 0;
     }
 
-    /// bytes held by the document (index, decoded strings, owned text)
+    /// bytes held by the document (index, decoded strings, owned text or image)
     std::size_t memory_usage() const noexcept
     {
         if (!m_data)
@@ -1011,9 +1047,10 @@ class basic_json_document
         }
         return sizeof(document_data) + (m_data->inline_capacity * sizeof(detail::view::node))
                + (m_data->nodes != m_data->inline_nodes ? m_data->node_capacity * sizeof(detail::view::node) : 0)
-               + m_data->arena.capacity() + m_data->owned.capacity()
+               + m_data->arena.capacity() + m_data->owned.capacity() + m_data->owned_image.capacity()
                + (m_data->indexes.capacity() * sizeof(document_data::object_index)) + (m_data->index_slots.capacity() * sizeof(std::uint32_t))
-               + (m_data->large_objects.capacity() * sizeof(std::uint32_t));
+               + (m_data->large_objects.capacity() * sizeof(std::uint32_t))
+               + (m_data->edits != nullptr ? m_data->edits->bytes : 0);
     }
 
     /// release unused capacity of the index and the decoded strings; like
@@ -1030,9 +1067,12 @@ class basic_json_document
 
         // allocate everything first, so that an exception leaves the document
         // unchanged
+        // (the decoded strings of a loaded image stay in the image)
+        const bool arena_in_use = d.base[1] == d.arena.data();
         const bool shrink_arena = d.arena.capacity() > d.arena.size();
-        std::vector<char> arena(shrink_arena ? d.arena : std::vector<char>());
-        const bool shrink_nodes = d.nodes != d.inline_nodes && d.node_count != d.node_capacity;
+        std::vector<char> arena(shrink_arena && arena_in_use ? d.arena : std::vector<char>());
+        // (edits link to the nodes of the index, which then stays in place)
+        const bool shrink_nodes = d.nodes != d.inline_nodes && d.node_count != d.node_capacity && d.edits == nullptr;
         const bool into_header = d.node_count <= d.inline_capacity;
         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>());
@@ -1051,7 +1091,10 @@ class basic_json_document
         if (shrink_arena)
         {
             d.arena.swap(arena);
-            d.base[1] = d.arena.data();
+            if (arena_in_use)
+            {
+                d.base[1] = d.arena.data();
+            }
         }
         if (d.indexes.capacity() > d.indexes.size())
         {
@@ -1063,9 +1106,239 @@ class basic_json_document
         }
     }
 
+    ////////////
+    // images //
+    ////////////
+
+    /// how load() checks an image (full, bounds, or none)
+    using image_check = detail::view::image_check;
+
+    /// The document as an image that load() reads without parsing: the node
+    /// index, the text, and the decoded strings. An edited document is
+    /// written in its current state (floats that are not finite become null,
+    /// as in dump()).
+    std::vector<std::uint8_t> save() const
+    {
+        if (NLOHMANN_VIEW_UNLIKELY(!m_data || m_data->discarded))
+        {
+            detail::view::throw_type_error(320, "cannot save a discarded json_document");
+        }
+        return detail::view::save_image(*m_data);
+    }
+
+    /// Read an image written by save(). The image is borrowed: it must stay
+    /// alive and unchanged while the document is used.
+    NLOHMANN_VIEW_NODISCARD
+    static basic_json_document load(const std::uint8_t* image, std::size_t size, const image_check check = image_check::full)
+    {
+        basic_json_document d;
+        d.ensure_data(nullptr, 0);
+        detail::view::load_image(*d.m_data, image, size, check);
+        return d;
+    }
+
+    /// read an image (borrowed)
+    NLOHMANN_VIEW_NODISCARD
+    static basic_json_document load(const std::vector<std::uint8_t>& image, const image_check check = image_check::full)
+    {
+        return load(image.data(), image.size(), check);
+    }
+
+    /// read an image and keep it (no copy)
+    NLOHMANN_VIEW_NODISCARD
+    static basic_json_document load(std::vector<std::uint8_t>&& image, const image_check check = image_check::full)
+    {
+        basic_json_document d;
+        d.ensure_data(nullptr, 0);
+        d.m_data->owned_image = std::move(image);
+        detail::view::load_image(*d.m_data, d.m_data->owned_image.data(), d.m_data->owned_image.size(), check);
+        return d;
+    }
+
+    ///////////
+    // edits //
+    ///////////
+
+    // The source text is never written; new values go to storage owned by
+    // the document. A view keeps referring to the same value: after an
+    // assignment it sees the new value, and edits elsewhere do not affect it.
+    // A view of an erased value keeps its last value. An edit of an
+    // array/object invalidates the iterators over it. Values are accepted as
+    // views (of any document), BasicJsonType values, and everything
+    // BasicJsonType can be constructed from.
+
+    using string_view_t = typename view_type::string_view_t;
+    using json_pointer = typename BasicJsonType::json_pointer;
+
+    /// replace a value (a view of this document); returns a view of it
+    template<typename V>
+    view_type set(view_type target, V&& value)
+    {
+        return editor().set(target, std::forward<V>(value));
+    }
+
+    /// set a member (added if missing; a null value becomes an object);
+    /// returns a view of the member value
+    template<typename V>
+    view_type set(view_type object, string_view_t key, V&& value)
+    {
+        return editor().set(object, key, std::forward<V>(value));
+    }
+
+    /// assign an existing array element; returns a view of it
+    template < typename I, typename V, typename std::enable_if < std::is_integral<I>::value && !std::is_same<I, bool>::value, int >::type = 0 >
+    view_type set(view_type array, I idx, V && value)
+    {
+        return editor().set(array, index(idx), std::forward<V>(value));
+    }
+
+    /// 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. 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)
+    {
+        if (ptr.empty())
+        {
+            return set(root(), std::forward<V>(value));
+        }
+        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);
+            if (idx == parent.size())
+            {
+                return push_back(parent, std::forward<V>(value));
+            }
+            return set(parent, idx, std::forward<V>(value));
+        }
+        return set(parent, string_view_t(token.data(), token.size()), std::forward<V>(value));
+    }
+
+    /// append to an array (a null value becomes an array); returns a view of
+    /// the new element
+    template<typename V>
+    view_type push_back(view_type array, V&& value)
+    {
+        return editor().push_back(array, std::forward<V>(value));
+    }
+
+    /// insert into an array before position idx (idx <= size()); returns a
+    /// view of the new element
+    template < typename I, typename V, typename std::enable_if < std::is_integral<I>::value && !std::is_same<I, bool>::value, int >::type = 0 >
+    view_type insert(view_type array, I idx, V && value)
+    {
+        return editor().insert(array, index(idx), std::forward<V>(value));
+    }
+
+    /// remove all members with this key; returns their number
+    std::size_t erase(view_type object, string_view_t key)
+    {
+        return editor().erase(object, key);
+    }
+
+    /// remove an array element
+    template < typename I, typename std::enable_if < std::is_integral<I>::value && !std::is_same<I, bool>::value, int >::type = 0 >
+    void erase(view_type array, I idx)
+    {
+        editor().erase(array, index(idx));
+    }
+
+    /// remove the value at a JSON pointer; returns the number of removed
+    /// values
+    std::size_t erase(const json_pointer& ptr)
+    {
+        if (ptr.empty())
+        {
+            detail::view::throw_out_of_range(405, "JSON pointer has no parent");
+        }
+        const view_type parent = root().at(ptr.parent_pointer());
+        const auto& token = ptr.back();
+        if (parent.is_array())
+        {
+            erase(parent, pointer_index(token));
+            return 1;
+        }
+        return erase(parent, string_view_t(token.data(), token.size()));
+    }
+
   private:
     using input_kind = detail::view::input_kind;
 
+    detail::view::editor<BasicJsonType, view_type> editor()
+    {
+        static_assert(Editable, "only an editable document can be edited: use basic_json_document<BasicJsonType, true> (json_editable_document)");
+        if (NLOHMANN_VIEW_UNLIKELY(!m_data || m_data->discarded))
+        {
+            detail::view::throw_invalid_iterator(202, "view does not belong to this document");
+        }
+        return detail::view::editor<BasicJsonType, view_type>(*m_data);
+    }
+
+    /// an index (out_of_range.401 if negative)
+    template<typename I>
+    static std::size_t index(I idx)
+    {
+        return index(idx, std::is_signed<I> {});
+    }
+
+    template<typename I>
+    static std::size_t index(I idx, std::true_type /*signed*/)
+    {
+        if (idx < 0)
+        {
+            detail::view::throw_out_of_range(401, detail::concat("array index ", std::to_string(idx), " is out of range"));
+        }
+        return static_cast<std::size_t>(idx);
+    }
+
+    template<typename I>
+    static std::size_t index(I idx, std::false_type /*unsigned*/)
+    {
+        return static_cast<std::size_t>(idx);
+    }
+
+    /// the array index of a JSON pointer token (json_pointer's rules)
+    template<typename StringType>
+    static std::size_t pointer_index(const StringType& token)
+    {
+        std::size_t idx = 0;
+        const detail::view::index_status status = detail::view::array_index(token, idx);
+        if (status != detail::view::index_status::ok)
+        {
+            detail::view::throw_array_index_error(status, token);
+        }
+        return idx;
+    }
+
     /// create the storage (sized for the input) on first use
     void ensure_data(const char* src, std::size_t size)
     {
@@ -1116,9 +1389,12 @@ class basic_json_document
         {
             d.owned.clear();
         }
+        d.owned_image.clear();
         d.src = src;
         d.size = size;
         d.node_count = 0;
+        d.edits.reset(); // (views of the previous text end here anyway)
+        d.base[2] = nullptr;
         d.arena.clear();
         d.indexes.clear();
         d.index_slots.clear();
@@ -1138,6 +1414,7 @@ class basic_json_document
         {
             d.base[0] = d.src;
             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;
@@ -1288,6 +1565,14 @@ using json_view = basic_json_view<json>;
 using ordered_json_document = basic_json_document<ordered_json>;
 /// a value of an ordered_json_document
 using ordered_json_view = basic_json_view<ordered_json>;
+/// an editable parsed JSON text for json
+using json_editable_document = basic_json_document<json, true>;
+/// a value of a json_editable_document
+using json_editable_view = basic_json_view<json, true>;
+/// an editable parsed JSON text for ordered_json
+using ordered_json_editable_document = basic_json_document<ordered_json, true>;
+/// a value of an ordered_json_editable_document
+using ordered_json_editable_view = basic_json_view<ordered_json, true>;
 
 NLOHMANN_JSON_NAMESPACE_END
 

single_include/nlohmann/json.hpp

@@ -27929,6 +27929,48 @@ inline char* write_shortest(char* first, const zmij::shortest_decimal d) noexcep
     return end + (three ? 5 : 4);
 }
 
+/// the powers of ten up to 10^16
+inline const std::array<std::uint64_t, 17>& powers_of_ten_16() noexcept
+{
+    static const std::array<std::uint64_t, 17> powers =
+    {
+        {
+            1u, 10u, 100u, 1000u, 10000u, 100000u, 1000000u, 10000000u, 100000000u, 1000000000u, 10000000000u,
+            100000000000u, 1000000000000u, 10000000000000u, 100000000000000u, 1000000000000000u, 10000000000000000u
+        }
+    };
+    return powers;
+}
+
+/*!
+@brief digits * 10^exp, as write_decimal() writes it, for the digits of a
+double that need no conversion (count digits, at most 15, the first not 0;
+trailing zeros allowed): extended to 16 digits and written by write_shortest()
+
+@return a pointer past the text; up to 41 bytes at @a first are written
+        (some beyond the returned end)
+*/
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_short_decimal(char* first, std::uint64_t digits, int count, int exp) noexcept
+{
+    JSON_ASSERT(digits >= powers_of_ten_16()[static_cast<std::size_t>(count - 1)] && count <= 15);
+    const int scale = 16 - count;
+    return write_shortest(first, zmij::shortest_decimal{digits * powers_of_ten_16()[static_cast<std::size_t>(scale)], exp - scale - 1, 0, false});
+}
+
+/// as write_short_decimal(), counting the digits (not 0, less than 10^15)
+JSON_HEDLEY_NON_NULL(1)
+JSON_HEDLEY_RETURNS_NON_NULL
+inline char* write_short_decimal(char* first, std::uint64_t digits, int exp) noexcept
+{
+    JSON_ASSERT(digits != 0 && digits < 1000000000000000u);
+    // floor(log10(2^bits)) + 1 digits, or one less
+    const int log2_bound = ((64 - count_leading_zeros(digits)) * 1233) >> 12;
+    const int count = log2_bound + (digits >= powers_of_ten_16()[static_cast<std::size_t>(log2_bound)] ? 1 : 0);
+    return write_short_decimal(first, digits, count, exp);
+}
+
 /*!
 @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)

tests/Makefile

@@ -10,7 +10,7 @@ CXXFLAGS += -std=c++11
 CPPFLAGS += -I ../single_include
 
 FUZZER_ENGINE = src/fuzzer-driver_afl.cpp
-FUZZERS = parse_afl_fuzzer parse_bson_fuzzer parse_cbor_fuzzer parse_msgpack_fuzzer parse_ubjson_fuzzer parse_bjdata_fuzzer parse_bon8_fuzzer parse_json_view_fuzzer
+FUZZERS = parse_afl_fuzzer parse_bson_fuzzer parse_cbor_fuzzer parse_msgpack_fuzzer parse_ubjson_fuzzer parse_bjdata_fuzzer parse_bon8_fuzzer parse_json_view_fuzzer json_view_image_fuzzer
 fuzzers: $(FUZZERS)
 
 parse_afl_fuzzer:
@@ -19,6 +19,9 @@ parse_afl_fuzzer:
 parse_json_view_fuzzer:
 	$(CXX) $(CXXFLAGS) $(CPPFLAGS) $(FUZZER_ENGINE) src/fuzzer-parse_json_view.cpp -o $@
 
+json_view_image_fuzzer:
+	$(CXX) $(CXXFLAGS) $(CPPFLAGS) $(FUZZER_ENGINE) src/fuzzer-json_view_image.cpp -o $@
+
 parse_bson_fuzzer:
 	$(CXX) $(CXXFLAGS) $(CPPFLAGS) $(FUZZER_ENGINE) src/fuzzer-parse_bson.cpp -o $@
 

tests/fuzzing.md

@@ -12,6 +12,12 @@ produces, and that a rejected input makes both parsers throw with an identical `
 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
+`load()`). It uses each input twice: as an image, which `load()` must either reject with `parse_error.116` or read
+safely (with `image_check::full`, the document must also serialize to the JSON it reads as), and as a JSON text, whose
+image must load and serialize to the same text. A corpus of images can be made from JSON files with a small program
+that calls `json_document::parse(text).save()`; plain JSON files work as well.
+
 ## What the fuzzers check
 
 Each fuzzer driver (`tests/src/fuzzer-parse_*.cpp`) parses its input twice: once with `allow_exceptions = false` and

tests/src/fuzzer-json_view_image.cpp

@@ -0,0 +1,95 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+/*
+This file implements a test of json_document images suitable for fuzz
+testing. The input is used twice:
+
+- as an image: json_document::load() with image_check::full must either throw
+  a parse_error or yield a document that serializes to the JSON text it reads
+  as; with image_check::bounds, reading and serializing must be safe (checked
+  by the sanitizers), and serializing may only throw type_error.316
+- as a JSON text: if json_document::parse() accepts it, the image of the
+  document must load (with every check) and serialize to the same text
+
+The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
+drivers.
+*/
+
+#include <cassert>
+#include <cstdint>
+#include <string>
+#include <vector>
+#include <nlohmann/json.hpp>
+#include <nlohmann/json_view.hpp>
+
+// the checks below are assertions; NDEBUG would compile them away
+#ifdef NDEBUG
+    #error "the fuzzer drivers must be built without NDEBUG"
+#endif
+
+using json = nlohmann::json;
+using json_document = nlohmann::json_document;
+using image_check = json_document::image_check;
+
+// see http://llvm.org/docs/LibFuzzer.html
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+{
+    // the input as an image
+    for (const image_check check :
+            {
+                image_check::full, image_check::bounds
+            })
+    {
+        json_document d;
+        try
+        {
+            d = json_document::load(data, size, check);
+        }
+        catch (const json::parse_error& e)
+        {
+            assert(e.id == 116);
+            continue;
+        }
+        std::string dumped;
+        try
+        {
+            dumped = d.root().dump();
+        }
+        catch (const json::type_error& e)
+        {
+            // invalid UTF-8 can only pass the bounds check
+            assert(check == image_check::bounds && e.id == 316);
+            continue;
+        }
+        const json j = d.root().materialize();
+        if (check == image_check::full)
+        {
+            assert(json::parse(dumped) == j);
+            // an image of the loaded document is the input
+            assert(d.save() == std::vector<std::uint8_t>(data, data + size));
+        }
+    }
+
+    // the input as a JSON text
+    const std::string text(reinterpret_cast<const char*>(data), size); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    const json_document parsed = json_document::parse(text, false);
+    if (!parsed.is_discarded())
+    {
+        const std::vector<std::uint8_t> image = parsed.save();
+        for (const image_check check :
+                {
+                    image_check::full, image_check::bounds, image_check::none
+                })
+        {
+            const json_document loaded = json_document::load(image, check);
+            assert(loaded.root().dump() == parsed.root().dump());
+        }
+    }
+    return 0;
+}

tests/src/json_view_test_helpers.hpp

@@ -15,6 +15,7 @@
 #include <nlohmann/json_view.hpp>
 
 #include <algorithm> // any_of
+#include <functional> // function
 #include <random> // mt19937
 #include <string> // string
 
@@ -86,4 +87,20 @@ inline bool has_duplicate_keys(const nlohmann::ordered_json_view& v)
         return e.is_structured() && has_duplicate_keys(e);
     });
 }
+
+#if !defined(JSON_NOEXCEPTION)
+// the exception a call throws, or "" if it throws none
+inline std::string exception_of_call(const std::function<void()>& f)
+{
+    try
+    {
+        f();
+    }
+    catch (const nlohmann::json::exception& e)
+    {
+        return e.what();
+    }
+    return "";
+}
+#endif
 } // namespace json_view_test

tests/src/unit-json_view_builder.cpp

@@ -377,7 +377,7 @@ TEST_CASE("json_view builder")
         const built shallow = build(nested, false, false, false);
         REQUIRE(shallow.ok);
         shallow.data->max_depth = 1;
-        CHECK(nlohmann::detail::view::materialize<json>(*shallow.data, shallow.data->nodes) == json::parse(nested));
+        CHECK(nlohmann::detail::view::materialize<json, false>(*shallow.data, shallow.data->nodes) == json::parse(nested));
 
         // the open containers beyond 64 levels live on the heap
         for (const std::size_t depth :

tests/src/unit-json_view_dump.cpp

@@ -94,6 +94,58 @@ TEST_CASE("json_view dump")
         CHECK(d.root().dump() == json::parse(text).dump());
         CHECK(d.root().dump() == "[1.5,100.0,0,-0.0,1.2345678901234568e+29,18446744073709551615,-9223372036854775808,0.1,1e-07,5e-324]");
         CHECK(d.root().dump(-1, ' ', false, json_view::number_format::source) == "[1.50,1E2,-0,-0.0,123456789012345678901234567890,18446744073709551615,-9223372036854775808,0.1,1e-7,5e-324]");
+        // also indented, and with ensure_ascii
+        CHECK(d.root().dump(0, ' ', false, json_view::number_format::source) == "[\n1.50,\n1E2,\n-0,\n-0.0,\n123456789012345678901234567890,\n18446744073709551615,\n-9223372036854775808,\n0.1,\n1e-7,\n5e-324\n]");
+        CHECK(d.root().dump(-1, ' ', true, json_view::number_format::source) == "[1.50,1E2,-0,-0.0,123456789012345678901234567890,18446744073709551615,-9223372036854775808,0.1,1e-7,5e-324]");
+
+        // float tokens of up to 17 significant digits in every spelling: those
+        // of at most 15 digits are written from their digits, the others
+        // through the conversion; both as dump() writes them
+        {
+            std::mt19937_64 tokens(1170); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+            // a number below n; the remainder is a std::uint64_t, which is
+            // std::size_t on some platforms and wider on others
+            const auto draw = [&tokens](std::size_t n)
+            {
+                const std::uint64_t r = tokens() % n;
+                return static_cast<std::size_t>(r);
+            };
+            std::string many_tokens = "[";
+            for (int i = 0; i < 20000; ++i)
+            {
+                const std::size_t length = 1 + draw(17);
+                std::string digits(1, static_cast<char>('1' + draw(9)));
+                for (std::size_t k = 1; k < length; ++k)
+                {
+                    digits += static_cast<char>('0' + draw(10));
+                }
+                digits += std::string(draw(4), '0'); // trailing zeros
+                std::string token = draw(3) == 0 ? "-" : "";
+                const std::size_t point = draw(digits.size() + 1);
+                if (point == 0)
+                {
+                    token += "0." + std::string(draw(5), '0') + digits;
+                }
+                else
+                {
+                    token += digits.substr(0, point) + (point < digits.size() ? "." + digits.substr(point) : "");
+                }
+                // an exponent that keeps the value between about 1e-320 and 1e300
+                const int exponent = static_cast<int>(draw(600)) - 300 - static_cast<int>(point);
+                if (draw(4) != 0)
+                {
+                    token += (draw(2) == 0 ? "e" : "E") + std::string(exponent >= 0 && draw(2) == 0 ? "+" : "") + std::to_string(exponent);
+                }
+                else if (point == digits.size())
+                {
+                    token += ".0"; // (a float, not an integer)
+                }
+                many_tokens += (i != 0 ? "," : "") + token;
+            }
+            many_tokens += ']';
+            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
         std::mt19937_64 rng(1170); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)

tests/src/unit-json_view_edit.cpp

@@ -0,0 +1,807 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json_view.hpp>
+using nlohmann::json;
+using nlohmann::ordered_json;
+using nlohmann::json_document;
+using nlohmann::json_editable_document;
+using nlohmann::json_editable_view;
+using nlohmann::ordered_json_document;
+using nlohmann::ordered_json_editable_document;
+using nlohmann::ordered_json_editable_view;
+using ptr_t = ordered_json::json_pointer;
+
+#include "json_view_test_helpers.hpp"
+#if !defined(JSON_NOEXCEPTION)
+    using json_view_test::exception_of_call;
+#endif
+
+#include <array>
+#include <cmath>
+#include <cstring>
+#include <cstdint>
+#include <iterator>
+#include <limits>
+#include <map>
+#include <random>
+#include <set>
+#include <string>
+#include <vector>
+
+namespace
+{
+std::uint32_t rng()
+{
+    static std::mt19937 generator(5295); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
+    // result_type is std::uint_fast32_t, which may be wider than 32 bits
+    const std::mt19937::result_type value = generator();
+    return static_cast<std::uint32_t>(value);
+}
+
+int r(int n)
+{
+    return static_cast<int>(rng() % static_cast<unsigned>(n));
+}
+
+int counter = 0;
+
+std::uint64_t bits(double x)
+{
+    std::uint64_t b = 0;
+    std::memcpy(&b, &x, sizeof(b));
+    return b;
+}
+
+std::string random_string()
+{
+    static const std::array<const char*, 15> pieces = {{"a", "Z", " ", "~", "\n", "\"", "\\", "/", "\xc3\xa9", "\xe3\x81\x82", "\xf0\x9f\x98\x80", "\x7f", "\x1f", "0", "key"}};
+    std::string s;
+    for (int i = r(3) == 0 ? r(30) : r(6); i > 0; --i)
+    {
+        s += pieces[static_cast<std::size_t>(r(15))];
+    }
+    return s;
+}
+
+ordered_json random_scalar()
+{
+    switch (r(9))
+    {
+        case 0:
+            return nullptr;
+        case 1:
+            return r(2) == 0;
+        case 2:
+            return static_cast<std::int64_t>(rng()) - 2147483648LL;
+        case 3:
+            return (static_cast<std::uint64_t>(rng()) * 4294967296ULL) + rng();
+        case 4:
+            return static_cast<double>(static_cast<std::int32_t>(rng())) / (1 + r(1000));
+        case 5:
+            return r(2) == 0 ? 1e300 * (r(2) == 0 ? 1 : -1) : 5e-324;
+        case 6:
+            return -0.0;
+        default:
+            return random_string();
+    }
+}
+
+ordered_json random_value(int depth)
+{
+    const int k = depth > 3 ? 4 : r(7);
+    if (k == 0)
+    {
+        ordered_json o = ordered_json::object();
+        for (int i = r(5); i > 0; --i)
+        {
+            o[random_string() + "#" + std::to_string(counter++)] = random_value(depth + 1);
+        }
+        return o;
+    }
+    if (k == 1)
+    {
+        ordered_json a = ordered_json::array();
+        for (int i = r(5); i > 0; --i)
+        {
+            a.push_back(random_value(depth + 1));
+        }
+        return a;
+    }
+    return random_scalar();
+}
+
+void collect(const ordered_json& j, const ptr_t& p, std::vector<ptr_t>& out)
+{
+    out.push_back(p);
+    if (j.is_object())
+    {
+        for (const auto& kv : j.items())
+        {
+            collect(kv.value(), p / kv.key(), out);
+        }
+    }
+    else if (j.is_array())
+    {
+        for (std::size_t i = 0; i < j.size(); ++i)
+        {
+            collect(j[i], p / i, out);
+        }
+    }
+}
+
+
+// the edited view and the ordered_json value read the same through the whole
+// read API
+void compare(const ordered_json_editable_view& v, const ordered_json& j)
+{
+    REQUIRE(v.type() == j.type());
+    REQUIRE(v.size() == j.size());
+    if (j.is_object())
+    {
+        auto jt = j.begin();
+        for (auto it = v.begin(); it != v.end(); ++it, ++jt)
+        {
+            CHECK(std::string(it.key().data(), it.key().size()) == jt.key());
+            CHECK(v[jt.key()].dump() == jt.value().dump());
+            CHECK(v.contains(jt.key()));
+            compare(*it, jt.value());
+        }
+    }
+    else if (j.is_array())
+    {
+        for (std::size_t i = 0; i < j.size(); ++i)
+        {
+            CHECK(v[i].dump() == j[i].dump());
+        }
+        std::size_t i = 0;
+        for (const auto e : v)
+        {
+            compare(e, j[i++]);
+        }
+        if (!j.empty())
+        {
+            CHECK(v.back().dump() == j.back().dump());
+        }
+    }
+    else if (j.is_string())
+    {
+        CHECK(v.get<std::string>() == j.get<std::string>());
+    }
+    else if (j.is_number_float())
+    {
+        CHECK(bits(v.get<double>()) == bits(j.get<double>()));
+    }
+    else if (j.is_number_integer())
+    {
+        CHECK(v.get<std::int64_t>() == j.get<std::int64_t>());
+        CHECK(v.get<std::uint64_t>() == j.get<std::uint64_t>());
+    }
+}
+
+// the text of j, in which some objects repeat a key of theirs after their
+// members: lookups of the edited document find the first member of a key, so
+// j (the first members) is what they must agree with, while parse() would
+// keep the last value
+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 = "{";
+        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();
+}
+
+// the number of members of an object view with this key, by iteration
+std::size_t occurrences(const ordered_json_editable_view& v, const std::string& key)
+{
+    std::size_t result = 0;
+    for (const auto& item : v.items())
+    {
+        result += std::string(item.key().data(), item.key().size()) == key ? 1u : 0u;
+    }
+    return result;
+}
+
+// every lookup of the edited view finds the first member of its key, which
+// the iteration of the view shows
+void check_lookups(const ordered_json_editable_view& v)
+{
+    if (v.is_object())
+    {
+        std::set<std::string> seen;
+        for (const auto item : v.items())
+        {
+            const std::string key(item.key().data(), item.key().size());
+            if (!seen.insert(key).second)
+            {
+                continue; // (not the first member of the key)
+            }
+            const ptr_t ptr = ptr_t() / key;
+            CAPTURE(key)
+            const ordered_json expected = item.value().materialize();
+            const ordered_json_editable_view m = v[key];
+            REQUIRE(!m.is_discarded());
+            CHECK(m.materialize() == expected);
+            CHECK(v.at(key).materialize() == expected);
+            CHECK(v[ptr].materialize() == expected);
+            CHECK(v.at(ptr).materialize() == expected);
+            CHECK(v.contains(key));
+            CHECK(v.contains(ptr));
+            CHECK(v.count(key) == occurrences(v, key));
+            const auto it = v.find(key);
+            REQUIRE(it != v.end());
+            CHECK((*it).materialize() == expected);
+            CHECK(v.value(ptr, ordered_json(nullptr)) == expected);
+            if (expected.is_string())
+            {
+                CHECK(v.value(key, std::string("-")) == expected.get<std::string>());
+            }
+            check_lookups(m);
+        }
+        CHECK(v["missing#key"].is_discarded());
+        CHECK(!v.contains("missing#key"));
+        CHECK(v.find("missing#key") == v.end());
+    }
+    else if (v.is_array())
+    {
+        for (std::size_t i = 0; i < v.size(); ++i) // NOLINT(modernize-loop-convert): both v[i] and v.at(i) are tested
+        {
+            check_lookups(v[i]);
+            check_lookups(v.at(i));
+        }
+    }
+}
+
+// every lookup of the edited view finds what the first members of j hold
+void check_first_members(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)
+            REQUIRE(v.contains(key));
+            CHECK(v.contains(ptr));
+            CHECK(v.count(key) == occurrences(v, key));
+            CHECK(v.find(key) != v.end());
+            CHECK(v.at(ptr).type() == kv.value().type());
+            check_first_members(v[key], kv.value());
+            check_first_members(v.at(key), kv.value());
+            check_first_members(v[ptr], kv.value());
+        }
+        CHECK(!v.contains("missing#key"));
+    }
+    else if (j.is_array())
+    {
+        REQUIRE(v.size() == j.size());
+        for (std::size_t i = 0; i < j.size(); ++i)
+        {
+            check_first_members(v[i], j[i]);
+        }
+    }
+    else
+    {
+        CHECK(v.materialize() == j);
+    }
+}
+
+// (for documents whose objects repeat keys: j holds the first members, the
+// lookups must find them; dump(), size(), and iteration list all members, but
+// materialize() keeps the last value of a key, as parse() does of the dump)
+void check_duplicates(const ordered_json_editable_document& d, const ordered_json& j)
+{
+    check_first_members(d.root(), j);
+    check_lookups(d.root());
+    CHECK(d.root().materialize() == ordered_json::parse(d.root().dump()));
+}
+
+void check_all(const ordered_json_editable_document& d, const ordered_json& j, bool deep)
+{
+    const std::string text = d.root().dump();
+    REQUIRE(text == j.dump());
+    CHECK(d.root().materialize() == j);
+    if (deep)
+    {
+        CHECK(d.root().dump(2) == j.dump(2));
+        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+        CHECK(d.root() == j);
+        compare(d.root(), j);
+        // a fresh document of the text reads the same
+        const ordered_json_document fresh = ordered_json_document::parse(text);
+        CHECK(fresh.root() == d.root());
+    }
+}
+} // namespace
+
+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 < 250; ++n)
+    {
+        // the last 100 documents repeat keys in some of their objects; j then
+        // holds the first member of each key, which the edits address
+        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)}});
+        }
+        if (duplicates)
+        {
+            j = ordered_json::parse(j.dump()); // (normalized as the document reads it)
+        }
+        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);
+        if (!duplicates)
+        {
+            j = ordered_json::parse(text);
+        }
+        const ordered_json_document other = ordered_json_document::parse(random_value(0).dump());
+        const int edits = 30;
+        for (int e = 0; e < edits; ++e)
+        {
+            std::vector<ptr_t> paths;
+            collect(j, ptr_t(), paths);
+            const ptr_t p = paths[static_cast<std::size_t>(r(static_cast<int>(paths.size())))];
+            const ordered_json& target = j[p];
+            const ordered_json_editable_view tv = d.root().at(p);
+            const int op = r(12);
+            {
+                if (op == 0) // assign a scalar
+                {
+                    const ordered_json v = random_scalar();
+                    if (v.is_string() && r(2) == 0)
+                    {
+                        d.set(tv, v.get<std::string>());
+                    }
+                    else if (v.is_number_unsigned() && r(2) == 0)
+                    {
+                        d.set(tv, v.get<std::uint64_t>());
+                    }
+                    else
+                    {
+                        d.set(tv, v);
+                    }
+                    j[p] = v;
+                }
+                else if (op == 1) // assign a new array/object (or anything), sometimes via the pointer API
+                {
+                    const ordered_json v = random_value(2);
+                    if (r(2) == 0)
+                    {
+                        d.set(p, v);
+                    }
+                    else
+                    {
+                        d.set(tv, v);
+                    }
+                    j[p] = v;
+                }
+                else if (op == 2) // copy a value of the same document
+                {
+                    const ptr_t& q = paths[static_cast<std::size_t>(r(static_cast<int>(paths.size())))];
+                    const ordered_json v = j[q];
+                    d.set(tv, d.root().at(q));
+                    j[p] = v;
+                }
+                else if (op == 3) // copy a value of another document
+                {
+                    d.set(tv, other.root());
+                    j[p] = other.root().materialize();
+                }
+                else if ((op == 4 || op == 5) && target.is_object()) // set a member (new or existing)
+                {
+                    std::string key = random_string() + "#" + std::to_string(counter++);
+                    if (op == 5 && !target.empty())
+                    {
+                        key = std::next(target.begin(), r(static_cast<int>(target.size()))).key();
+                    }
+                    const ordered_json v = random_value(2);
+                    d.set(tv, key, v);
+                    j[p][key] = v;
+                }
+                else if (op == 6 && target.is_object() && !target.empty()) // erase a member
+                {
+                    const std::string key = std::next(target.begin(), r(static_cast<int>(target.size()))).key();
+                    if (r(2) == 0)
+                    {
+                        d.erase(tv, key);
+                    }
+                    else
+                    {
+                        d.erase(p / key);
+                    }
+                    j[p].erase(key);
+                }
+                else if (op == 7 && (target.is_array() || target.is_null())) // push_back
+                {
+                    const ordered_json v = random_value(2);
+                    d.push_back(tv, v);
+                    j[p].push_back(v);
+                }
+                else if (op == 8 && target.is_array()) // insert
+                {
+                    const auto i = static_cast<std::size_t>(r(static_cast<int>(target.size()) + 1));
+                    const ordered_json v = random_value(2);
+                    d.insert(tv, i, v);
+                    j[p].insert(j[p].begin() + static_cast<std::ptrdiff_t>(i), v);
+                }
+                else if (op == 9 && target.is_array() && !target.empty()) // erase an element
+                {
+                    const auto i = static_cast<std::size_t>(r(static_cast<int>(target.size())));
+                    if (r(2) == 0)
+                    {
+                        d.erase(tv, i);
+                    }
+                    else
+                    {
+                        d.erase(p / i);
+                    }
+                    j[p].erase(i);
+                }
+                else if (op == 10 && target.is_array() && !target.empty()) // assign an element
+                {
+                    const auto i = static_cast<std::size_t>(r(static_cast<int>(target.size())));
+                    const ordered_json v = random_value(2);
+                    d.set(tv, i, v);
+                    j[p][i] = v;
+                }
+                else if (op == 11) // a held view sees the assignment
+                {
+                    const ordered_json v = random_value(2);
+                    const ordered_json_editable_view held = d.root().at(p);
+                    d.set(p, v);
+                    j[p] = v;
+                    CHECK(held.dump() == v.dump());
+                }
+                else
+                {
+                    continue;
+                }
+            }
+            CAPTURE(p.to_string())
+            CAPTURE(op)
+            if (duplicates)
+            {
+                check_duplicates(d, j);
+            }
+            else
+            {
+                check_all(d, j, e % 8 == 7 || e == edits - 1);
+            }
+        }
+    }
+}
+
+TEST_CASE("json_view edits: errors")
+{
+    SECTION("an empty document")
+    {
+        json_editable_document d;
+        CHECK_THROWS_WITH_AS(d.set(d.root(), 1), "[json.exception.invalid_iterator.202] view does not belong to this document", json::invalid_iterator&);
+    }
+
+    json_editable_document d = json_editable_document::parse(R"({"o": {"a": 1}, "a": [1, 2], "n": 1, "z": null})");
+    const json_editable_view root = d.root();
+    const json_document other = json_document::parse("[1]");
+    json_editable_document other_editable = json_editable_document::parse("[1]");
+
+    CHECK_THROWS_WITH_AS(d.set(other_editable.root(), 1), "[json.exception.invalid_iterator.202] view does not belong to this document", json::invalid_iterator&);
+    CHECK_THROWS_WITH_AS(d.set(json_editable_view(), 1), "[json.exception.invalid_iterator.202] view does not belong to this document", json::invalid_iterator&);
+    CHECK_THROWS_WITH_AS(d.set(root["a"], "k", 1), "[json.exception.type_error.305] cannot use operator[] with a string argument with array", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.set(root["o"], 0, 1), "[json.exception.type_error.305] cannot use operator[] with a numeric argument with object", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.set(root["a"], 2, 1), "[json.exception.out_of_range.401] array index 2 is out of range", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.set(root["a"], -1, 1), "[json.exception.out_of_range.401] array index -1 is out of range", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.push_back(root["o"], 1), "[json.exception.type_error.308] cannot use push_back() with object", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.insert(root["n"], 0, 1), "[json.exception.type_error.309] cannot use insert() with number", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.insert(root["a"], 3, 1), "[json.exception.out_of_range.401] array index 3 is out of range", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.erase(root["n"], "k"), "[json.exception.type_error.307] cannot use erase() with number", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.erase(root["o"], 0), "[json.exception.type_error.307] cannot use erase() with object", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.erase(root["a"], 2), "[json.exception.out_of_range.401] array index 2 is out of range", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.erase(json::json_pointer("")), "[json.exception.out_of_range.405] JSON pointer has no parent", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.erase(json::json_pointer("/missing/x")), "[json.exception.out_of_range.403] key 'missing' not found", json::out_of_range&);
+    CHECK_THROWS_WITH_AS(d.set(json::json_pointer("/a/01"), 1), "[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'", json::parse_error&);
+    CHECK_THROWS_WITH_AS(d.set(root, json_editable_view()), "[json.exception.type_error.302] type must be a value, but is discarded", json::type_error&);
+    CHECK_THROWS_WITH_AS(d.set(root, json::binary({1, 2})), "[json.exception.type_error.319] cannot store a binary value in a json_document", json::type_error&);
+
+#if !defined(JSON_NOEXCEPTION)
+    // invalid UTF-8 is rejected when it enters the document, with the error
+    // basic_json::dump() reports for the same string
+    for (const std::string bad :
+            {"\xC3\x28", "a\xE2\x28\xA1", "\xF0\x28\x8C\xBC", "\xE2\x82", "x\xF0\x9F\x98", "\xFF", "\xED\xA0\x80", "\xC0\xAF"
+            })
+    {
+        CAPTURE(bad)
+        const std::string expected = exception_of_call([&]
+        {
+            const std::string text = json(bad).dump();
+            static_cast<void>(text);
+        });
+        CHECK(!expected.empty());
+        CHECK(exception_of_call([&] { d.set(root["z"], bad); }) == expected);
+        CHECK(exception_of_call([&] { d.set(root["o"], bad, 1); }) == expected);
+        CHECK(exception_of_call([&] { d.set(root["z"], json{{"k", bad}}); }) == expected);
+    }
+#endif
+    // nothing of the failed edits is visible
+    CHECK(root.dump() == R"({"o":{"a":1},"a":[1,2],"n":1,"z":null})");
+    static_cast<void>(other);
+}
+
+#if !defined(JSON_NOEXCEPTION)
+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 first member wins, however the
+// object is stored
+template<typename View>
+void check_first_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")));
+    std::size_t members_a = 0;
+    for (const auto& item : o.items())
+    {
+        members_a += std::string(item.key().data(), item.key().size()) == "a" ? 1u : 0u;
+    }
+    CHECK(o.count("a") == members_a); // every member, unlike the lookups
+}
+} // 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_first_wins(d.root(), 1);
+        CHECK(d.root().size() == 3);
+        CHECK(d.root().dump() == R"({"a":1,"b":2,"a":3})");
+        CHECK(d.root().materialize()["a"] == 3); // (parse() keeps the last value)
+
+        // an edit of a value does not move the object
+        d.set(d.root()["b"], 5);
+        check_first_wins(d.root(), 1);
+        d.set(d.root()["a"], 4); // the member that lookups find
+        check_first_wins(d.root(), 4);
+        CHECK(d.root().dump() == R"({"a":4,"b":5,"a":3})");
+
+        // an appended member moves it
+        d.set(d.root(), "c", true);
+        check_first_wins(d.root(), 4);
+        CHECK(d.root().size() == 4);
+        CHECK(d.root().dump() == R"({"a":4,"b":5,"a":3,"c":true})");
+        d.set(d.root()["a"], 6);
+        check_first_wins(d.root(), 6);
+        CHECK(d.root().dump() == R"({"a":6,"b":5,"a":3,"c":true})");
+        d.set(json::json_pointer("/a"), 7);
+        check_first_wins(d.root(), 7);
+    }
+
+    SECTION("set assigns the member that lookups find")
+    {
+        // the key stays where its first occurrence is, 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>() == 1);
+        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":4},"b":2,"a":{"x":3}})");
+        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_first_wins(d.root(), 1);
+        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_first_wins(d.root(), 0);
+        CHECK(d.root()["k7"].get_string() == "first");
+        CHECK(d.root()["k199"].get<int>() == 199);
+
+        // a value assigned in place: the index stays in use
+        d.set(d.root()["a"], 3);
+        check_first_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_first_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() == "first");
+        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_first_wins(d.root()[0], 1);
+        check_first_wins(d.root()[1], 3);
+        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_first_wins(d.root()[1], 1);
+        check_first_wins(d.root()[2], 3);
+        CHECK(d.root()[3]["a"].get<int>() == 6);
+        d.set(d.root()[1], "a", 8);
+        check_first_wins(d.root()[1], 8);
+        CHECK(d.root()[1].dump() == R"({"a":8})");
+        d.erase(d.root(), 0);
+        check_first_wins(d.root()[1], 3);
+        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_first_wins(d.root()["copy"][0], 1);
+        check_first_wins(d.root()["o"]["b"], 3);
+        check_first_wins(d.root()["o"], 5);
+        d.set(d.root()["o"]["b"], "c", 0);
+        check_first_wins(d.root()["o"]["b"], 3);
+        d.set(d.root()["o"], "d", 0);
+        check_first_wins(d.root()["o"], 5);
+        CHECK(d.root()["o"]["b"]["a"].get<int>() == 3);
+        CHECK(d.root()["o"]["d"].get<int>() == 0);
+    }
+}

tests/src/unit-json_view_edit_values.cpp

@@ -0,0 +1,357 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json_view.hpp>
+using nlohmann::json;
+using nlohmann::json_document;
+using nlohmann::json_editable_document;
+using nlohmann::json_editable_view;
+
+#include "json_view_test_helpers.hpp"
+#if !defined(JSON_NOEXCEPTION)
+    using json_view_test::exception_of_call;
+#endif
+
+#include <array>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <limits>
+#include <map>
+#include <string>
+#include <utility>
+#include <vector>
+
+// These tests were split off unit-json_view_edit.cpp, whose object file got too
+// large for the MinGW linker (see json_view_test_helpers.hpp).
+
+TEST_CASE("json_view edits: views and values")
+{
+    SECTION("a value that is no longer part of the document")
+    {
+        json_editable_document d = json_editable_document::parse("[[[1,2]]]");
+        const json_editable_view inner = d.root()[0][0];
+        d.set(d.root()[0], json::array({7}));
+        d.set(inner, 5);
+        CHECK(d.root().dump() == "[[7]]");
+        CHECK(inner.get<int>() == 5);
+    }
+
+    SECTION("views keep referring to their value")
+    {
+        json_editable_document d = json_editable_document::parse(R"({"a": [10, 20, 30], "b": {"c": "text"}})");
+        const json_editable_view a = d.root()["a"];
+        const json_editable_view twenty = a[1];
+        const json_editable_view c = d.root()["b"]["c"];
+        d.insert(a, 0, 5);
+        d.push_back(a, 40);
+        CHECK(twenty.get<int>() == 20);
+        CHECK(a[2].get<int>() == 20);
+        d.erase(a, 2);
+        CHECK(twenty.get<int>() == 20); // an erased value keeps its last value
+        d.set(c, 7);
+        CHECK(c.get<int>() == 7); // a held view sees an assignment
+        d.set(d.root()["b"], json::array({1, 2}));
+        CHECK(d.root()["b"].dump() == "[1,2]");
+        CHECK(d.root().dump() == R"({"a":[5,10,30,40],"b":[1,2]})");
+        CHECK(d.root()["a"][0].source_offset() == static_cast<std::size_t>(-1)); // a new value
+        CHECK(d.root()["a"][1].source_offset() != static_cast<std::size_t>(-1));
+    }
+
+    SECTION("strings stay valid while more edits come")
+    {
+        json_editable_document d = json_editable_document::parse("[]");
+        const auto first = d.push_back(d.root(), std::string(100, 'x')).get_string();
+        for (int i = 0; i < 1000; ++i)
+        {
+            d.push_back(d.root(), std::string(static_cast<std::size_t>(i % 50), 'y'));
+        }
+        CHECK(std::string(first.data(), first.size()) == std::string(100, 'x'));
+        CHECK(d.root().size() == 1001);
+    }
+
+    SECTION("numbers")
+    {
+        json_editable_document d = json_editable_document::parse(R"([1.50, 1E2, 3])");
+        d.set(d.root(), 2, 0.1);
+        d.push_back(d.root(), std::numeric_limits<double>::quiet_NaN());
+        d.push_back(d.root(), -std::numeric_limits<double>::infinity());
+        d.push_back(d.root(), (std::numeric_limits<std::uint64_t>::max)());
+        d.push_back(d.root(), (std::numeric_limits<std::int64_t>::min)());
+        CHECK(d.root().dump() == "[1.5,100.0,0.1,null,null,18446744073709551615,-9223372036854775808]");
+        CHECK(d.root().dump(-1, ' ', false, json_editable_view::number_format::source) == "[1.50,1E2,0.1,null,null,18446744073709551615,-9223372036854775808]");
+        CHECK(std::isnan(d.root()[3].get<double>()));
+        CHECK(std::isinf(d.root()[4].get<double>()));
+        CHECK(d.root()[2].number_token() == "0.1");
+        CHECK(d.root()[5].get<std::uint64_t>() == 18446744073709551615u);
+        CHECK(d.root()[6].number_token() == "-9223372036854775808");
+        CHECK(d.root().materialize().dump() == json::parse(R"([1.5, 100.0, 0.1, null, null, 18446744073709551615, -9223372036854775808])").dump());
+    }
+
+    SECTION("numbers of other float types")
+    {
+        // doubles have their own path to the output; other float types are
+        // written as basic_json writes them, non-finite values as null
+        using json_float = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
+        using document_float = nlohmann::basic_json_document<json_float, true>;
+        document_float d = document_float::parse("[1.5]");
+        d.push_back(d.root(), std::numeric_limits<float>::quiet_NaN());
+        d.push_back(d.root(), -std::numeric_limits<float>::infinity());
+        CHECK(d.root().dump() == "[1.5,null,null]");
+        CHECK(d.root().dump(2) == json_float::parse("[1.5, null, null]").dump(2));
+    }
+
+    SECTION("nulls become containers, and the root can be replaced")
+    {
+        json_editable_document d = json_editable_document::parse("[null, null]");
+        d.set(d.root()[0], "k", 1);
+        d.push_back(d.root()[1], true);
+        CHECK(d.root().dump() == R"([{"k":1},[true]])");
+        d.set(d.root(), "scalar");
+        CHECK(d.root().dump() == R"("scalar")");
+        d.set(d.root(), json{{"x", {1, 2}}});
+        d.set(json::json_pointer("/x/-"), 3);
+        d.set(json::json_pointer("/x/3"), 4); // the size of the array appends too
+        d.set(json::json_pointer("/y"), false);
+        CHECK(d.root().dump() == R"({"x":[1,2,3,4],"y":false})");
+        CHECK(d.erase(json::json_pointer("/x/0")) == 1);
+        CHECK(d.erase(json::json_pointer("/y")) == 1);
+        CHECK(d.erase(json::json_pointer("/nothing")) == 0);
+        CHECK(d.root().dump() == R"({"x":[2,3,4]})");
+    }
+
+    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
+        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);
+        CHECK(d.root().dump() == R"({"b":2})");
+    }
+
+    SECTION("values from other documents")
+    {
+        const json_document source = json_document::parse(R"({"list": [1, "two", {"three": 3.5}], "text": "a\nb"})");
+        json_editable_document edited = json_editable_document::parse("[0]");
+        edited.set(edited.root(), 0, json{{"inner", {1, 2}}});
+        json_editable_document d = json_editable_document::parse("{}");
+        d.set(d.root(), "copy", source.root()["list"]);
+        d.set(d.root(), "text", source.root()["text"]);
+        d.set(d.root(), "edited", edited.root()[0]);
+        d.set(d.root(), "self", d.root()["copy"]);
+        // (a raw string with a backslash must not be a macro argument: MSVC C2017)
+        const std::string expected = R"({"copy":[1,"two",{"three":3.5}],"text":"a\nb","edited":{"inner":[1,2]},"self":[1,"two",{"three":3.5}]})";
+        CHECK(d.root().dump() == expected);
+        CHECK(d.root()["copy"] == source.root()["list"]);
+        CHECK(source.root()["list"] == d.root()["self"]);
+        CHECK(d.root() != source.root());
+    }
+
+    SECTION("large objects")
+    {
+        std::string text = "{";
+        for (int i = 0; i < 200; ++i)
+        {
+            text += (i != 0 ? ",\"k" : "\"k") + std::to_string(i) + "\":" + std::to_string(i);
+        }
+        text += '}';
+        json_editable_document d = json_editable_document::parse(text);
+        d.set(d.root(), "k7", "seven"); // assigned in place: the index stays in use
+        CHECK(d.root()["k7"].get_string() == "seven");
+        d.set(d.root(), "new", 1); // appended: the members move, the lookup is linear
+        CHECK(d.root()["new"].get<int>() == 1);
+        CHECK(d.root()["k199"].get<int>() == 199);
+        d.erase(d.root(), "k0");
+        CHECK(!d.root().contains("k0"));
+        CHECK(d.root().size() == 200);
+    }
+
+    SECTION("reuse and memory")
+    {
+        json_editable_document d = json_editable_document::parse("[1, 2, 3]");
+        const std::size_t before = d.memory_usage();
+        for (int i = 0; i < 100; ++i)
+        {
+            d.push_back(d.root(), "some text");
+        }
+        CHECK(d.memory_usage() > before);
+        const json_editable_view first = d.root()[0];
+        d.shrink_to_fit(); // (with edits, the index stays in place)
+        CHECK(first.get<int>() == 1);
+        d.read(std::string("[true]"));
+        CHECK(d.root().dump() == "[true]");
+        d.push_back(d.root(), false);
+        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"]}])");
+}
+#endif

tests/src/unit-to_chars.cpp

@@ -846,3 +846,85 @@ TEST_CASE("choice of the conversion")
         DOCTEST_MSVC_SUPPRESS_WARNING_POP
     }
 }
+
+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::string
+    {
+        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 {buf.data(), end};
+    };
+    const auto written_counted = [](std::uint64_t digits, int count, int exp) -> std::string
+    {
+        std::array<char, 64> buf{};
+        char* const end = nlohmann::detail::dtoa_impl::write_short_decimal(buf.data(), digits, count, exp);
+        return {buf.data(), end};
+    };
+    const auto expected = [](std::uint64_t digits, int exp) -> std::string
+    {
+        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 {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);
+        }
+    }
+}