Merge branch 'develop' into claude/todo-191-plan-508110

Conflicts: none textual. Follow-up fixes for develop's changes: - docs/mkdocs/docs/api/ordered_map/index.md: develop's new paragraph (#5609) was written for api/ordered_map.md; fixed its relative ordered_json.md link for the page's new location, plus two pre-existing links from an earlier merge (ordered_json.md, features/object_order.md) - tools/api_checker/api_surface.json: regenerated with libclang 18.1.1 on Linux (swap() noexcept now includes json_base_class_t; new integral-key contains/count/find/value overloads) Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-01 04:00:31 +00:00 · 2026-09-30 20:36:12 +02:00 · 2026-09-28 22:22:46 +02:00 · 2026-09-28 18:42:34 +02:00 · 2026-09-27 21:37:14 +02:00 · 2026-09-27 18:09:03 +02:00
160 changed files with 72545 additions and 1400 deletions
@@ -0,0 +1,81 @@
+name: "Check API documentation"
+
+on:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  check_api_docs:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@bf7454d06d71f1098171f2acdf0cd4708d7b5920 # v2.20.0
+        with:
+          egress-policy: audit
+
+      - name: Checkout pull request
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+
+      - name: Install clang
+        # Used only as a subprocess for `clang++ -E -v` system-include-path discovery in
+        # extract_api.py; it does not need to version-match the pinned libclang pip wheel
+        # below, which does the actual AST parsing. Do not "fix" this to be version-matched.
+        run: sudo apt-get update && sudo apt-get install -y clang
+
+      - name: Install Python dependencies
+        run: pip install -r tools/api_checker/requirements.txt
+
+      - name: Extract API and regenerate the committed surface file
+        run: |
+          python3 tools/api_checker/extract_api.py \
+            --header include/nlohmann/json.hpp \
+            --include include \
+            --output /tmp/api_snapshot.json \
+            --surface-output tools/api_checker/api_surface.json
+
+      - name: "Check API documentation (Phase 1: advisory)"
+        # Surfaces missing/broken @sa links without failing the job while the backlog from the
+        # initial AST-based rollout is burned down. See tools/api_checker/POLICY.md and the PR
+        # that introduced this workflow for the two-phase rollout plan.
+        continue-on-error: true
+        run: |
+          python3 tools/api_checker/check_docs.py \
+            --snapshot /tmp/api_snapshot.json
+
+      - name: Check macro documentation (advisory only)
+        # Cross-checks docs/mkdocs/docs/api/macros/ pages against #define sites. Only checks the
+        # documented-macro-still-exists direction; never blocks CI. See POLICY.md.
+        run: python3 tools/api_checker/check_macros.py
+
+      - name: Check for uncommitted API surface changes
+        id: diff
+        run: |
+          mkdir -p ${{ github.workspace }}/patch
+          git diff --patch --no-color -- tools/api_checker/api_surface.json > ${{ github.workspace }}/patch/api_surface.patch
+          if [ -s ${{ github.workspace }}/patch/api_surface.patch ]; then
+            echo "tools/api_checker/api_surface.json is out of date. Diff:"
+            cat ${{ github.workspace }}/patch/api_surface.patch
+            echo "has_diff=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "has_diff=false" >> "$GITHUB_OUTPUT"
+          fi
+
+      # Uploaded so contributors can fix their PR with `git apply api_surface.patch`
+      # instead of installing libclang locally.
+      - name: Upload patch
+        if: steps.diff.outputs.has_diff == 'true'
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: api-surface-patch
+          path: patch/api_surface.patch
+
+      - name: Fail if API surface file is not up to date
+        # Unlike the doc-backlog check above, this is purely mechanical regeneration with no
+        # backlog to phase in -- blocking from the start, matching check_amalgamation.yml's
+        # precedent. Contributors who add/remove/rename public API must regenerate and commit
+        # tools/api_checker/api_surface.json as part of their PR.
+        if: steps.diff.outputs.has_diff == 'true'
+        run: exit 1
@@ -100,7 +100,7 @@ jobs:
    container: ubuntu:focal
    strategy:
      matrix:
-        target: [ci_cmake_flags, ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_noglobaludls, ci_test_disableenumserialization, ci_test_disabletuplereferenceconversion, ci_test_skiplibraryversioncheck, ci_test_simdutf, ci_test_strict_nul_handling, ci_test_no_thread_local]
+        target: [ci_cmake_flags, ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_noglobaludls, ci_test_disableenumserialization, ci_test_skiplibraryversioncheck, ci_test_simdutf, ci_test_strict_nul_handling, ci_test_no_thread_local]
    steps:
      - name: Install build-essential
        run: apt-get update ; apt-get install -y build-essential unzip wget git libssl-dev
@@ -3,6 +3,7 @@
 *.gcno
 *.gcda
 .DS_Store
+__pycache__/

 /.idea
 /cmake-build-*
@@ -43,5 +44,9 @@ venv

 nlohmann_json.spdx

+# api_checker: ephemeral, location/doc-status-sensitive working file (not the committed
+# release-tracking artifact -- see tools/api_checker/api_surface.json for that)
+/tools/api_checker/api_snapshot.json
+
 # Bazel-related
 MODULE.bazel.lock
@@ -55,7 +55,6 @@ option(JSON_Diagnostic_Positions           "Enable diagnostic positions." OFF)
 option(JSON_GlobalUDLs                     "Place user-defined string literals in the global namespace." ON)
 option(JSON_ImplicitConversions            "Enable implicit conversions." ON)
 option(JSON_DisableEnumSerialization       "Disable default integer enum serialization." OFF)
-option(JSON_DisableTupleReferenceConversion "Disable conversion from a one-element tuple of a JSON reference." OFF)
 option(JSON_LegacyDiscardedValueComparison "Enable legacy discarded value comparison." OFF)
 option(JSON_Install                        "Install CMake targets during install step." ${MAIN_PROJECT})
 option(JSON_MultipleHeaders                "Use non-amalgamated version of the library." ON)
@@ -102,10 +101,6 @@ if (JSON_DisableEnumSerialization)
    message(STATUS "Enum integer serialization is disabled (JSON_DISABLE_ENUM_SERIALIZATION=1)")
 endif()

-if (JSON_DisableTupleReferenceConversion)
-    message(STATUS "Tuple reference conversion is disabled (JSON_DISABLE_TUPLE_REFERENCE_CONVERSION=1)")
-endif()
-
 if (JSON_LegacyDiscardedValueComparison)
    message(STATUS "Legacy discarded value comparison enabled (JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1)")
 endif()
@@ -148,7 +143,6 @@ target_compile_definitions(
    $<$<NOT:$<BOOL:${JSON_GlobalUDLs}>>:JSON_USE_GLOBAL_UDLS=0>
    $<$<NOT:$<BOOL:${JSON_ImplicitConversions}>>:JSON_USE_IMPLICIT_CONVERSIONS=0>
    $<$<BOOL:${JSON_DisableEnumSerialization}>:JSON_DISABLE_ENUM_SERIALIZATION=1>
-    $<$<BOOL:${JSON_DisableTupleReferenceConversion}>:JSON_DISABLE_TUPLE_REFERENCE_CONVERSION=1>
    $<$<BOOL:${JSON_Diagnostics}>:JSON_DIAGNOSTICS=1>
    $<$<BOOL:${JSON_Diagnostic_Positions}>:JSON_DIAGNOSTIC_POSITIONS=1>
    $<$<BOOL:${JSON_LegacyDiscardedValueComparison}>:JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1>
@@ -106,7 +106,7 @@ Thanks everyone!

 :books: If you want to **learn more** about how to use the library, check out the rest of the [**README**](#examples), have a look at [**code examples**](https://github.com/nlohmann/json/tree/develop/docs/mkdocs/docs/examples), or browse through the [**help pages**](https://json.nlohmann.me).

-:construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/) or have a look at the [quick reference](#quick-reference) below.
+:construction: If you want to understand the **API** better, check out the [**API Reference**](https://json.nlohmann.me/api/basic_json/) or have a look at the [quick reference](#quick-reference) below. The public API surface is derived mechanically and checked for documentation coverage by the tooling in [`tools/api_checker/`](tools/api_checker/), whose [POLICY.md](tools/api_checker/POLICY.md) defines what counts as public API and what stability is guaranteed.

 :bug: If you found a **bug**, please check the [**FAQ**](https://json.nlohmann.me/home/faq/) if it is a known issue or the result of a design decision. Please also have a look at the [**issue list**](https://github.com/nlohmann/json/issues) before you [**create a new issue**](https://github.com/nlohmann/json/issues/new/choose). Please provide as much information as possible to help us understand and reproduce your issue.

@@ -276,20 +276,6 @@ add_custom_target(ci_test_disableenumserialization
    COMMENT "Compile and test with enum serialization disabled"
 )

-###############################################################################
-# Disable conversion from a one-element tuple of a JSON reference.
-###############################################################################
-
-add_custom_target(ci_test_disabletuplereferenceconversion
-    COMMAND ${CMAKE_COMMAND}
-    -DCMAKE_BUILD_TYPE=Debug -GNinja
-    -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_DisableTupleReferenceConversion=ON
-    -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_disabletuplereferenceconversion
-    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_disabletuplereferenceconversion
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_disabletuplereferenceconversion && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
-    COMMENT "Compile and test with tuple reference conversion disabled"
-)
-
 ###############################################################################
 # Skip the multiple-inclusion library version check.
 ###############################################################################
@@ -210,7 +210,6 @@ INSERT INTO searchIndex(name, type, path) VALUES ('JSON_CATCH_USER', 'Macro', 'a
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DIAGNOSTICS', 'Macro', 'api/macros/json_diagnostics/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DIAGNOSTIC_POSITIONS', 'Macro', 'api/macros/json_diagnostic_positions/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DISABLE_ENUM_SERIALIZATION', 'Macro', 'api/macros/json_disable_enum_serialization/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DISABLE_TUPLE_REFERENCE_CONVERSION', 'Macro', 'api/macros/json_disable_tuple_reference_conversion/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_HAS_CPP_11', 'Macro', 'api/macros/json_has_cpp_11/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_HAS_CPP_14', 'Macro', 'api/macros/json_has_cpp_11/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_HAS_CPP_17', 'Macro', 'api/macros/json_has_cpp_11/index.html');
@@ -159,8 +159,6 @@ basic_json(basic_json&& other) noexcept;
    - `CompatibleType` is not `basic_json` (to avoid hijacking copy/move constructors),
    - `CompatibleType` is not a different `basic_json` type (i.e. with different template arguments)
    - `CompatibleType` is not a `basic_json` nested type (e.g., `json_pointer`, `iterator`, etc.)
-    - if [`JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../macros/json_disable_tuple_reference_conversion.md) is defined
-      to `1`: `CompatibleType` is not a one-element `std::tuple` holding a reference to `basic_json`
    - `json_serializer<U>` (with `U = uncvref_t<CompatibleType>`) has a `to_json(basic_json_t&, CompatibleType&&)`
       method

@@ -422,7 +420,9 @@ basic_json(basic_json&& other) noexcept;
 1. Since version 1.0.0.
 2. Since version 1.0.0.
 3. Since version 2.1.0.
-4. Since version 3.2.0.
+4. Since version 3.2.0. Also initializes the position reported by
+   [`start_pos()`](start_pos.md)/[`end_pos()`](end_pos.md) from `val` when
+   [`JSON_DIAGNOSTIC_POSITIONS`](../macros/json_diagnostic_positions.md) is enabled, since version 3.12.0.
 5. Since version 1.0.0.
 6. Since version 1.0.0.
 7. Since version 1.0.0. Fixed in version 3.13.0 to also check the iterator range for binary values; before, a range
@@ -0,0 +1,38 @@
+# <small>nlohmann::basic_json::</small>bjdata_version_t
+
+```cpp
+enum class bjdata_version_t
+{
+    draft2,
+    draft3,
+};
+```
+
+This enumeration is used in the [`to_bjdata`](to_bjdata.md) function to choose which draft version of
+the BJData specification to encode ND-array extensions for:
+
+draft2
+:   encode using the BJData Draft 2 ND-array format
+
+draft3
+:   encode using the BJData Draft 3 ND-array format
+
+## Examples
+
+??? example
+
+    The example shows how `bjdata_version_t` selects the BJData draft used by `to_bjdata`.
+
+    ```cpp
+    --8<-- "examples/bjdata_version_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/bjdata_version_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.12.0.
@@ -0,0 +1,32 @@
+# <small>nlohmann::basic_json::</small>initializer_list_t
+
+```cpp
+using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>;
+```
+
+The type used for the initializer-list [constructor](basic_json.md) (overload 5) and for functions
+such as [`operator=`](operator=.md) that accept a braced-init-list of JSON values. Each element wraps a
+`basic_json` value or something convertible to one, deferring the decision of whether the list should be
+parsed as a JSON array or a JSON object to the constructor itself.
+
+See the [constructor](basic_json.md) documentation for how `initializer_list_t` values are interpreted.
+
+## Examples
+
+??? example
+
+    The example shows how an `initializer_list_t` is used to construct a JSON value.
+
+    ```cpp
+    --8<-- "examples/initializer_list_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/initializer_list_t.output"
+    ```
+
+## Version history
+
+- Since version 1.0.0.
@@ -0,0 +1,31 @@
+# <small>nlohmann::basic_json::</small>json_sax_t
+
+```cpp
+using json_sax_t = json_sax<basic_json>;
+```
+
+The [`json_sax`](../json_sax/index.md) interface bound to this `basic_json` specialization, i.e. with
+`BasicJsonType` fixed to `basic_json`. Used as the SAX interface type by [`sax_parse`](sax_parse.md) and
+other SAX-based parsing functions.
+
+See [`nlohmann::json_sax`](../json_sax/index.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `json_sax_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.
@@ -51,3 +51,5 @@ Linear.
 ## Version history

 - Added in version 1.0.0.
+- The `noexcept` specification was extended to also depend on
+  [`json_base_class_t`](json_base_class_t.md)'s move-assignment in version 3.11.3.
@@ -85,3 +85,8 @@ Linear in the size of the JSON value.
 - Since version 1.0.0.
 - Macros `JSON_EXPLICIT`/[`JSON_USE_IMPLICIT_CONVERSIONS`](../macros/json_use_implicit_conversions.md) added
  in version 3.9.0.
+- The exclusion of `std::any` from this conversion became conditional on
+  [`JSON_HAS_STATIC_RTTI`](../macros/json_has_static_rtti.md) in version 3.11.3.
+- `std::optional<T>` excluded from this conversion in version 3.13.0; use
+  [`get<std::optional<T>>()`](get.md)/[`get_to()`](get_to.md) instead (see
+  [Converting values](../../features/conversions.md)).
@@ -56,8 +56,6 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va

 - Throws [`other_error.502`](../../home/exceptions.md#jsonexceptionother_error502) if `use_type` is true and `use_size`
  is false.
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
-  not valid UTF-8

 ## Complexity

@@ -91,5 +89,4 @@ Linear in the size of the JSON value `j`.
 ## Version history

 - Added in version 3.11.0.
- BJData version parameter (for draft3 binary encoding) added in version 3.12.0.
- Throwing `type_error.316` for a string or object key that is not valid UTF-8 added in version 3.13.0.
+- BJData version parameter (for draft3 binary encoding) added in version 3.12.0.
@@ -46,8 +46,6 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [`out_of_range.415`](../../home/exceptions.md#jsonexceptionout_of_range415) if the subtype of a binary value
  exceeds 255, the maximum of the BSON binary subtype; example:
  `"subtype 70000 is too large for the BSON binary subtype (max 255)"`
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key is
-  not valid UTF-8

 ## Complexity

@@ -84,5 +82,3 @@ pass before anything is written.
 - Added in version 3.4.0.
 - Linear in the size of `j`, and no longer limited by the call stack for deeply nested values, since version 3.13.0.
 - `out_of_range.415` is now detected before anything is written, like the other exceptions above, since version 3.13.0.
- Throwing `type_error.316` for a string value or object key that is not valid UTF-8, detected before anything is
-  written, added in version 3.13.0.
@@ -35,11 +35,6 @@ The exact mapping and its limitations are described on a [dedicated page](../../

 Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

-## Exceptions
-
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
-  not valid UTF-8
-
 ## Complexity

 Linear in the size of the JSON value `j`.
@@ -73,4 +68,3 @@ Linear in the size of the JSON value `j`.

 - Added in version 2.0.9.
 - Compact representation of floating-point numbers added in version 3.8.0.
- Throwing `type_error.316` for a string or object key that is not valid UTF-8 added in version 3.13.0.
@@ -49,8 +49,6 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va

 - Throws [`other_error.502`](../../home/exceptions.md#jsonexceptionother_error502) if `use_type` is true and `use_size`
  is false.
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
-  not valid UTF-8

 ## Complexity

@@ -84,4 +82,3 @@ Linear in the size of the JSON value `j`.
 ## Version history

 - Added in version 3.1.0.
- Throwing `type_error.316` for a string or object key that is not valid UTF-8 added in version 3.13.0.
@@ -0,0 +1,32 @@
+# <small>nlohmann::byte_container_with_subtype::</small>container_type
+
+```cpp
+using container_type = BinaryType;
+```
+
+The type of the underlying binary container, forwarded from the `BinaryType` template parameter that
+`byte_container_with_subtype` is instantiated with. `byte_container_with_subtype` publicly inherits from
+`container_type`.
+
+See [`basic_json::binary_t`](../basic_json/binary_t.md) for the type typically used to instantiate
+`BinaryType`.
+
+## Examples
+
+??? example
+
+    The example shows the type `container_type`.
+
+    ```cpp
+    --8<-- "examples/byte_container_with_subtype__container_type.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/byte_container_with_subtype__container_type.output"
+    ```
+
+## Version history
+
+- Since version 3.8.0.
@@ -0,0 +1,45 @@
+# <small>nlohmann::byte_container_with_subtype::</small>operator==
+
+```cpp
+bool operator==(const byte_container_with_subtype& rhs) const;
+```
+
+Compares two `byte_container_with_subtype` values for equality by comparing the underlying binary
+container, the subtype, and whether a subtype is set.
+
+## Parameters
+
+`rhs` (in)
+:   value to compare `*this` against
+
+## Return value
+
+whether `*this` and `rhs` are equal
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear in the size of the underlying binary container.
+
+## Examples
+
+??? example
+
+    The example demonstrates comparing `byte_container_with_subtype` values.
+
+    ```cpp
+    --8<-- "examples/byte_container_with_subtype__operator_eq.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/byte_container_with_subtype__operator_eq.output"
+    ```
+
+## Version history
+
+- Since version 3.8.0.
@@ -0,0 +1,45 @@
+# <small>nlohmann::byte_container_with_subtype::</small>operator!=
+
+```cpp
+bool operator!=(const byte_container_with_subtype& rhs) const;
+```
+
+Compares two `byte_container_with_subtype` values for inequality. Implemented as the negation of
+[`operator==`](operator_eq.md).
+
+## Parameters
+
+`rhs` (in)
+:   value to compare `*this` against
+
+## Return value
+
+whether `*this` and `rhs` are not equal
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear in the size of the underlying binary container.
+
+## Examples
+
+??? example
+
+    The example demonstrates comparing `byte_container_with_subtype` values.
+
+    ```cpp
+    --8<-- "examples/byte_container_with_subtype__operator_ne.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/byte_container_with_subtype__operator_ne.output"
+    ```
+
+## Version history
+
+- Since version 3.8.0.
@@ -0,0 +1,28 @@
+# <small>nlohmann::byte_container_with_subtype::</small>subtype_type
+
+```cpp
+using subtype_type = std::uint64_t;
+```
+
+The type used to store the optional binary subtype tag. See [`subtype`](subtype.md) and
+[`set_subtype`](set_subtype.md).
+
+## Examples
+
+??? example
+
+    The example shows the type `subtype_type`.
+
+    ```cpp
+    --8<-- "examples/byte_container_with_subtype__subtype_type.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/byte_container_with_subtype__subtype_type.output"
+    ```
+
+## Version history
+
+- Since version 3.8.0.
@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>binary_t
+
+```cpp
+using binary_t = typename BasicJsonType::binary_t;
+```
+
+The type used by the [`binary`](binary.md) callback for JSON binary values, forwarded from the
+`BasicJsonType` template parameter.
+
+See [`basic_json::binary_t`](../basic_json/binary_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `binary_t` and its relation to `basic_json::binary_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__binary_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__binary_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.8.0.
@@ -0,0 +1,33 @@
+# <small>nlohmann::json_sax::</small>json_sax
+
+```cpp
+// (1)
+json_sax() = default;
+
+// (2)
+json_sax(const json_sax&) = default;
+
+// (3)
+json_sax(json_sax&&) noexcept = default;
+```
+
+1. Default constructor.
+2. Copy constructor.
+3. Move constructor.
+
+`json_sax` is a pure abstract base class with no data members of its own, so all three constructors are
+defaulted and only exist to make derived SAX consumers explicitly copyable/movable.
+
+## Exception safety
+
+No-throw guarantee: none of these constructors throw exceptions.
+
+## Complexity
+
+Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.2.0.
@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>number_float_t
+
+```cpp
+using number_float_t = typename BasicJsonType::number_float_t;
+```
+
+The type used by the [`number_float`](number_float.md) callback for JSON floating-point numbers,
+forwarded from the `BasicJsonType` template parameter.
+
+See [`basic_json::number_float_t`](../basic_json/number_float_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `number_float_t` and its relation to `basic_json::number_float_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__number_float_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__number_float_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.
@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>number_integer_t
+
+```cpp
+using number_integer_t = typename BasicJsonType::number_integer_t;
+```
+
+The type used by the [`number_integer`](number_integer.md) callback for JSON integer numbers, forwarded
+from the `BasicJsonType` template parameter.
+
+See [`basic_json::number_integer_t`](../basic_json/number_integer_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `number_integer_t` and its relation to `basic_json::number_integer_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__number_integer_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__number_integer_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.
@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>number_unsigned_t
+
+```cpp
+using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+```
+
+The type used by the [`number_unsigned`](number_unsigned.md) callback for JSON unsigned integer numbers,
+forwarded from the `BasicJsonType` template parameter.
+
+See [`basic_json::number_unsigned_t`](../basic_json/number_unsigned_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `number_unsigned_t` and its relation to `basic_json::number_unsigned_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__number_unsigned_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__number_unsigned_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.
@@ -0,0 +1,29 @@
+# <small>nlohmann::json_sax::</small>operator=
+
+```cpp
+// (1)
+json_sax& operator=(const json_sax&) = default;
+
+// (2)
+json_sax& operator=(json_sax&&) noexcept = default;
+```
+
+1. Copy assignment operator.
+2. Move assignment operator.
+
+`json_sax` is a pure abstract base class with no data members of its own, so both assignment operators
+are defaulted and only exist to make derived SAX consumers explicitly copy-/move-assignable.
+
+## Exception safety
+
+No-throw guarantee: neither operator throws exceptions.
+
+## Complexity
+
+Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.2.0.
@@ -0,0 +1,30 @@
+# <small>nlohmann::json_sax::</small>string_t
+
+```cpp
+using string_t = typename BasicJsonType::string_t;
+```
+
+The type used by the [`string`](string.md) and [`key`](key.md) callbacks for JSON strings and object
+keys, forwarded from the `BasicJsonType` template parameter.
+
+See [`basic_json::string_t`](../basic_json/string_t.md) for more information.
+
+## Examples
+
+??? example
+
+    The example shows the type `string_t` and its relation to `basic_json::string_t`.
+
+    ```cpp
+    --8<-- "examples/json_sax__string_t.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/json_sax__string_t.output"
+    ```
+
+## Version history
+
+- Added in version 3.2.0.
@@ -0,0 +1,22 @@
+# <small>nlohmann::json_sax::</small>~json_sax
+
+```cpp
+virtual ~json_sax() = default;
+```
+
+Destructor. Virtual to allow proper destruction of derived SAX consumer classes through a
+pointer/reference to `json_sax`.
+
+## Exception safety
+
+No-throw guarantee: this destructor never throws exceptions.
+
+## Complexity
+
+Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.2.0.
@@ -53,7 +53,6 @@ header. See also the [macro overview page](../../features/macros.md).

 - [**JSON_BRACE_INIT_COPY_SEMANTICS**](json_brace_init_copy_semantics.md) - opt in to copy/move semantics for single-element brace initialization
 - [**JSON_DISABLE_ENUM_SERIALIZATION**](json_disable_enum_serialization.md) - switch off default serialization/deserialization functions for enums
- [**JSON_DISABLE_TUPLE_REFERENCE_CONVERSION**](json_disable_tuple_reference_conversion.md) - switch off conversion from a one-element tuple of a JSON reference
 - [**JSON_USE_IMPLICIT_CONVERSIONS**](json_use_implicit_conversions.md) - control implicit conversions

 ## Comparison behavior
@@ -1,114 +0,0 @@
-# JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
-
-```cpp
-#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION /* value */
-```
-
-When defined to `1`, a `basic_json` value can no longer be constructed from a one-element `std::tuple` whose element is
-a reference to that `basic_json` type, such as `std::tuple<json&>`, `std::tuple<const json&>`, or `std::tuple<json&&>`.
-These are the tuples created by `std::forward_as_tuple(j)`.
-
-## Default definition
-
-The default value is `0` (disabled — existing behavior is preserved).
-
-```cpp
-#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 0
-```
-
-## Notes
-
-!!! note "Background"
-
-    By default, `basic_json` can be constructed from any `std::tuple` whose elements can be converted to JSON; the result
-    is an array. This includes `std::tuple<json&>`, which becomes a one-element array.
-
-    `std::tuple` only converts another tuple element by element if its element type cannot be constructed from the whole
-    source tuple. Because `json` *can* be constructed from `std::tuple<json&>`, `std::tuple` instead converts the whole
-    tuple into a single `json` value. This has two surprising effects:
-
-    ```cpp
-    json j = true;
-
-    // rejected by some standard libraries (e.g., libc++); with others, the
-    // reference binds to a temporary that is destroyed right away
-    std::tuple<const json&> t1(std::forward_as_tuple(j));
-
-    // compiles, but std::get<0>(t2) is [true], not true
-    std::tuple<json> t2(std::forward_as_tuple(j));
-    ```
-
-    Enabling this macro removes the conversion, so both tuples are converted element by element: `std::get<0>(t1)`
-    refers to `j`, and `std::get<0>(t2)` is a copy of `j` (see [#2226](https://github.com/nlohmann/json/issues/2226)).
-
-!!! warning "Opt-in only"
-
-    This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no effect.
-
-!!! note "Affected conversions"
-
-    Only one-element tuples holding a reference to the **same** `basic_json` type are affected. Constructing a JSON value
-    from them no longer compiles:
-
-    ```cpp
-    json j = true;
-    json a = std::forward_as_tuple(j);  // error with the macro enabled
-    json b = json::array({j});          // use this instead: [true]
-    ```
-
-    Tuples holding a JSON value (`std::make_tuple(j)`), tuples with more than one element, and tuples holding references
-    to other types (including other `basic_json` specializations) are converted to arrays as before.
-
-!!! hint "CMake option"
-
-    This behavior can also be controlled with the CMake option
-    [`JSON_DisableTupleReferenceConversion`](../../integration/cmake.md#json_disabletuplereferenceconversion)
-    (`OFF` by default) which defines `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION` accordingly.
-
-## Examples
-
-??? example "Default behavior (macro not defined)"
-
-    ```cpp
-    #include <nlohmann/json.hpp>
-
-    using json = nlohmann::json;
-
-    int main()
-    {
-        json j = true;
-
-        std::tuple<json> t(std::forward_as_tuple(j));
-        // std::get<0>(t) is [true] -- the whole tuple was converted
-    }
-    ```
-
-??? example "Conversion disabled (macro defined to 1)"
-
-    ```cpp
-    #define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 1
-    #include <nlohmann/json.hpp>
-
-    using json = nlohmann::json;
-
-    int main()
-    {
-        json j = true;
-
-        std::tuple<json> t(std::forward_as_tuple(j));
-        // std::get<0>(t) is true -- a copy of j
-
-        std::tuple<const json&> r(std::forward_as_tuple(j));
-        // std::get<0>(r) refers to j
-    }
-    ```
-
-## See also
-
- [**basic_json(CompatibleType&&)**](../basic_json/basic_json.md) - the affected constructor
- [:simple-cmake: JSON_DisableTupleReferenceConversion](../../integration/cmake.md#json_disabletuplereferenceconversion) -
-  CMake option to control the macro
-
-## Version history
-
- Added in version 3.13.0.
@@ -8,16 +8,16 @@ This type preserves the insertion order of object keys.

 ## Iterator invalidation

-The type is based on [`ordered_map`](ordered_map.md) which in turn uses a `std::vector` to store object elements.
+The type is based on [`ordered_map`](ordered_map/index.md) which in turn uses a `std::vector` to store object elements.
 Therefore, adding object elements can yield a reallocation in which case all iterators (including the
 [`end()`](basic_json/end.md) iterator) and all references to the elements are invalidated. Also, any iterator or
 reference after the insertion point will point to the same index, which is now a different value.

 ## Complexity

-[`ordered_map`](ordered_map.md) has no lookup index: every key-based object operation is a linear scan, so building or
+[`ordered_map`](ordered_map/index.md) has no lookup index: every key-based object operation is a linear scan, so building or
 parsing an object of `n` keys costs O(n²) rather than O(n log n). See
-[`ordered_map` complexity](ordered_map.md#complexity) for the per-operation table and for measured numbers.
+[`ordered_map` complexity](ordered_map/index.md#complexity) for the per-operation table and for measured numbers.

 ## Examples

@@ -37,7 +37,7 @@ parsing an object of `n` keys costs O(n²) rather than O(n log n). See

 ## See also

- [ordered_map](ordered_map.md)
+- [ordered_map](ordered_map/index.md)
 - [Object Order](../features/object_order.md)

 ## Version history
@@ -0,0 +1,28 @@
+# <small>nlohmann::ordered_map::</small>Container
+
+```cpp
+using Container = std::vector<std::pair<const Key, T>, Allocator>;
+```
+
+The base container type that `ordered_map` publicly inherits from. Elements are stored in insertion
+order as `#!cpp std::pair<const Key, T>` entries in a `std::vector`.
+
+## Examples
+
+??? example
+
+    The example shows the type `Container`.
+
+    ```cpp
+    --8<-- "examples/ordered_map__Container.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__Container.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
@@ -0,0 +1,61 @@
+# <small>nlohmann::ordered_map::</small>at
+
+```cpp
+// (1)
+T& at(const key_type& key);
+const T& at(const key_type& key) const;
+
+// (2)
+template<class KeyType>
+T& at(KeyType&& key);
+template<class KeyType>
+const T& at(KeyType&& key) const;
+```
+
+1. Returns a reference to the value mapped to `key`.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup, e.g. looking up by a `#!cpp const char*` without constructing a temporary
+   `key_type`). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to find
+
+## Return value
+
+reference to the mapped value of the element with key equal to `key`
+
+## Exceptions
+
+Throws `std::out_of_range` if no element with key `key` exists.
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `at` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__at.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__at.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.1 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.
@@ -0,0 +1,53 @@
+# <small>nlohmann::ordered_map::</small>count
+
+```cpp
+// (1)
+size_type count(const key_type& key) const;
+
+// (2)
+template<class KeyType>
+size_type count(KeyType&& key) const;
+```
+
+1. Returns the number of elements with key equal to `key` (0 or 1, since keys are unique).
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the elements to count
+
+## Return value
+
+number of elements with key equal to `key` (0 or 1)
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `count` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__count.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__count.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.1 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.
@@ -0,0 +1,58 @@
+# <small>nlohmann::ordered_map::</small>emplace
+
+```cpp
+// (1)
+std::pair<iterator, bool> emplace(const key_type& key, T&& t);
+
+// (2)
+template<class KeyType>
+std::pair<iterator, bool> emplace(KeyType&& key, T&& t);
+```
+
+1. Inserts `#!cpp {key, t}` if no element with an equal key already exists (per [`key_compare`](key_compare.md)),
+   appending it at the end to preserve insertion order. If an equal key already exists, does nothing.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to insert
+
+`t` (in)
+:   value of the element to insert
+
+## Return value
+
+pair of an iterator to the (possibly newly inserted) element, and a `bool` that is `true` if insertion
+took place and `false` if an element with an equal key already existed
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `emplace` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__emplace.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__emplace.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.
@@ -0,0 +1,75 @@
+# <small>nlohmann::ordered_map::</small>erase
+
+```cpp
+// (1)
+size_type erase(const key_type& key);
+
+// (2)
+template<class KeyType>
+size_type erase(KeyType&& key);
+
+// (3)
+iterator erase(iterator pos);
+
+// (4)
+iterator erase(iterator first, iterator last);
+```
+
+1. Removes the element with key equal to `key`, if any, preserving the relative order of the remaining
+   elements.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+3. Removes the element at `pos`.
+4. Removes the elements in range `[first, last)`.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to remove
+
+`pos` (in)
+:   iterator to the element to remove
+
+`first` (in)
+:   iterator to the first element to remove
+
+`last` (in)
+:   iterator one past the last element to remove
+
+## Return value
+
+1. number of elements removed (0 or 1)
+2. number of elements removed (0 or 1)
+3. iterator following the removed element
+4. iterator following the last removed element
+
+## Complexity
+
+Linear in the number of elements (elements after the removed one(s) are shifted to keep storage
+contiguous).
+
+## Examples
+
+??? example
+
+    The example shows how `erase` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__erase.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__erase.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.
@@ -0,0 +1,56 @@
+# <small>nlohmann::ordered_map::</small>find
+
+```cpp
+// (1)
+iterator find(const key_type& key);
+const_iterator find(const key_type& key) const;
+
+// (2)
+template<class KeyType>
+iterator find(KeyType&& key);
+template<class KeyType>
+const_iterator find(KeyType&& key) const;
+```
+
+1. Returns an iterator to the element with key equal to `key`, or `end()` if no such element exists.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to find
+
+## Return value
+
+iterator to the element with key equal to `key`, or `end()` if not found
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `find` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__find.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__find.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.1 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.
@@ -6,7 +6,7 @@ template<class Key, class T, class IgnoredLess = std::less<Key>,
 struct ordered_map : std::vector<std::pair<const Key, T>, Allocator>;
 ```

-A minimal map-like container that preserves insertion order for use within [`nlohmann::ordered_json`](ordered_json.md)
+A minimal map-like container that preserves insertion order for use within [`nlohmann::ordered_json`](../ordered_json.md)
 (`nlohmann::basic_json<ordered_map>`).

 ## Template parameters
@@ -30,19 +30,19 @@ case all iterators (including the `end()` iterator) and all references to the el

 When the storage grows, the keys are copied and the mapped values are moved to the new storage. A plain `std::vector`
 would copy the whole elements instead, because their `#!cpp const` keys make them not nothrow move constructible; for
-[`ordered_json`](ordered_json.md), this would be a deep copy of every nested value. The values are only copied if
+[`ordered_json`](../ordered_json.md), this would be a deep copy of every nested value. The values are only copied if
 `T` is not default constructible or not nothrow move assignable.

 ## Member types

 - **key_type** - key type (`Key`)
 - **mapped_type** - mapped type (`T`)
- **Container** - base container type (`#!cpp std::vector<std::pair<const Key, T>, Allocator>`)
+- [**Container**](Container.md) - base container type (`#!cpp std::vector<std::pair<const Key, T>, Allocator>`)
 - **iterator**
 - **const_iterator**
 - **size_type**
 - **value_type**
- **key_compare** - key comparison function
+- [**key_compare**](key_compare.md) - key comparison function
 ```cpp
 std::equal_to<Key>  // until C++14

@@ -51,15 +51,16 @@ std::equal_to<>     // since C++14

 ## Member functions

- (constructor)
- (destructor)
- **emplace**
- **operator\[\]**
- **at**
- **erase**
- **count**
- **find**
- **insert**
+- [(constructor)](ordered_map.md)
+- [(destructor)](~ordered_map.md)
+- [**operator=**](operator=.md)
+- [**emplace**](emplace.md)
+- [**operator\[\]**](operator[].md)
+- [**at**](at.md)
+- [**erase**](erase.md)
+- [**count**](count.md)
+- [**find**](find.md)
+- [**insert**](insert.md)

 ## Exception safety

@@ -89,7 +90,7 @@ This differs from `#!cpp std::map`, where the same operations are O(log n).
 !!! warning "Quadratic cost of building large objects"

    Because every insertion scans all elements inserted so far, building an object of `n` distinct keys costs
-    **O(n²)** in total. This applies to filling an [`ordered_json`](ordered_json.md) object key by key as well as to
+    **O(n²)** in total. This applies to filling an [`ordered_json`](../ordered_json.md) object key by key as well as to
    parsing one, since the parser inserts each key as it is read.

    The cost is negligible for the object sizes typically found in configuration files or API payloads, but it grows
@@ -106,7 +107,7 @@ This differs from `#!cpp std::map`, where the same operations are O(log n).
    If key order matters for objects of that size, consider a container with a lookup index, such as
    [`tsl::ordered_map`](https://github.com/Tessil/ordered-map)
    ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)), as the object type -- see
-    [object order](../features/object_order.md).
+    [object order](../../features/object_order.md).

 ## Examples

@@ -126,10 +127,10 @@ This differs from `#!cpp std::map`, where the same operations are O(log n).

 ## See also

- [ordered_json](ordered_json.md)
+- [ordered_json](../ordered_json.md)

 ## Version history

- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](ordered_json.md).
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
 - Added **key_compare** member in version 3.11.0.
 - Changed in version 3.13.0: growing the storage moves the mapped values instead of copying them.
@@ -0,0 +1,63 @@
+# <small>nlohmann::ordered_map::</small>insert
+
+```cpp
+// (1)
+std::pair<iterator, bool> insert(value_type&& value);
+std::pair<iterator, bool> insert(const value_type& value);
+
+// (2)
+template<typename InputIt>
+void insert(InputIt first, InputIt last);
+```
+
+1. Inserts `value` if no element with an equal key already exists (per [`key_compare`](key_compare.md)),
+   appending it at the end to preserve insertion order. If an equal key already exists, does nothing.
+2. Inserts the elements from range `[first, last)`, in iteration order, applying the same equal-key rule
+   as (1) to each element.
+
+## Template parameters
+
+`InputIt`
+:   an input iterator type
+
+## Parameters
+
+`value` (in)
+:   value to insert
+
+`first` (in)
+:   iterator to the first element to insert
+
+`last` (in)
+:   iterator one past the last element to insert
+
+## Return value
+
+1. pair of an iterator to the (possibly newly inserted) element, and a `bool` that is `true` if insertion
+   took place and `false` if an element with an equal key already existed
+2. (none)
+
+## Complexity
+
+1. Linear in the number of elements.
+2. Linear in the distance between `first` and `last`, times linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `insert` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__insert.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__insert.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.1 to implement [`nlohmann::ordered_json`](../ordered_json.md).
@@ -0,0 +1,34 @@
+# <small>nlohmann::ordered_map::</small>key_compare
+
+```cpp
+using key_compare = std::equal_to<Key>;  // until C++14
+
+using key_compare = std::equal_to<>;     // since C++14
+```
+
+The comparator used to determine key equality when looking up elements. Unlike `std::map`, `ordered_map`
+uses linear search with `key_compare` rather than an ordering relation, since element order reflects
+insertion order rather than key order.
+
+Since C++14, the transparent `#!cpp std::equal_to<>` is used, which enables heterogeneous lookup (e.g.
+looking up by a `#!cpp const char*` key without constructing a temporary `Key`).
+
+## Examples
+
+??? example
+
+    The example shows how `key_compare` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__key_compare.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__key_compare.output"
+    ```
+
+## Version history
+
+- Added in version 3.11.0.
@@ -0,0 +1,32 @@
+# <small>nlohmann::ordered_map::</small>operator=
+
+```cpp
+// (1)
+ordered_map& operator=(const ordered_map& other);
+
+// (2)
+ordered_map& operator=(ordered_map&& other) noexcept(std::is_nothrow_move_assignable<Container>::value);
+```
+
+1. Copy assignment operator.
+2. Move assignment operator.
+
+## Parameters
+
+`other` (in)
+:   value to assign from
+
+## Return value
+
+`*this`
+
+## Complexity
+
+1. Linear in the size of `other`.
+2. Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
@@ -0,0 +1,62 @@
+# <small>nlohmann::ordered_map::</small>operator[]
+
+```cpp
+// (1)
+T& operator[](const key_type& key);
+const T& operator[](const key_type& key) const;
+
+// (2)
+template<class KeyType>
+T& operator[](KeyType&& key);
+template<class KeyType>
+const T& operator[](KeyType&& key) const;
+```
+
+1. Returns a reference to the value mapped to `key`, inserting a default-constructed `T` (non-`const`
+   overload only) if no such element exists yet.
+2. Same as (1), but for any `KeyType` comparable to `key_type` via [`key_compare`](key_compare.md)
+   (heterogeneous lookup). Only participates in overload resolution if `KeyType` is usable as a key type.
+
+## Template parameters
+
+`KeyType`
+:   a type comparable to `key_type` via [`key_compare`](key_compare.md)
+
+## Parameters
+
+`key` (in)
+:   key of the element to find or insert
+
+## Return value
+
+reference to the mapped value of the element with key equal to `key`
+
+## Exceptions
+
+The `const` overloads throw `std::out_of_range` if no element with key `key` exists (they delegate to
+[`at`](at.md)).
+
+## Complexity
+
+Linear in the number of elements.
+
+## Examples
+
+??? example
+
+    The example shows how `operator[]` is used.
+
+    ```cpp
+    --8<-- "examples/ordered_map__operator_idx.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/ordered_map__operator_idx.output"
+    ```
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
+- Overload (2) added in version 3.11.0.
@@ -0,0 +1,66 @@
+# <small>nlohmann::ordered_map::</small>ordered_map
+
+```cpp
+// (1)
+ordered_map() noexcept(noexcept(Container()));
+
+// (2)
+explicit ordered_map(const Allocator& alloc) noexcept(noexcept(Container(alloc)));
+
+// (3)
+template <class It>
+ordered_map(It first, It last, const Allocator& alloc = Allocator());
+
+// (4)
+ordered_map(std::initializer_list<value_type> init, const Allocator& alloc = Allocator());
+
+// (5)
+ordered_map(const ordered_map&) = default;
+
+// (6)
+ordered_map(ordered_map&&) noexcept(std::is_nothrow_move_constructible<Container>::value) = default;
+```
+
+1. Default constructor. Creates an empty `ordered_map`.
+2. Creates an empty `ordered_map` using the given allocator.
+3. Creates an `ordered_map` from the elements in range `[first, last)`, inserted in iteration order.
+4. Creates an `ordered_map` from an initializer list of key/value pairs, inserted in list order.
+5. Copy constructor.
+6. Move constructor.
+
+These constructors are declared explicitly (rather than inherited via `#!cpp using Container::Container`)
+because older compilers (GCC <= 5.5, Xcode <= 9.4) do not handle the inherited constructors correctly.
+
+## Template parameters
+
+`It`
+:   an input iterator type
+
+## Parameters
+
+`alloc` (in)
+:   allocator to use for the underlying container
+
+`first` (in)
+:   iterator to the first element to insert
+
+`last` (in)
+:   iterator one past the last element to insert
+
+`init` (in)
+:   initializer list of key/value pairs to insert
+
+## Complexity
+
+1. Constant.
+2. Constant.
+3. Linear in the distance between `first` and `last`.
+4. Linear in the size of `init`.
+5. Linear in the size of `other`.
+6. Constant.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
@@ -0,0 +1,17 @@
+# <small>nlohmann::ordered_map::</small>~ordered_map
+
+```cpp
+~ordered_map() = default;
+```
+
+Destroys the `ordered_map` and frees all allocated memory.
+
+## Complexity
+
+Linear in the number of elements.
+
+<!-- NOLINT Examples -->
+
+## Version history
+
+- Added in version 3.9.0 to implement [`nlohmann::ordered_json`](../ordered_json.md).
@@ -0,0 +1,21 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // an empty binary value is encoded differently by the two drafts:
+    // draft2 omits the optimized type marker for an empty byte array,
+    // while draft3 always writes it
+    json j = json::binary({});
+
+    // encode using BJData draft2 (the default)
+    auto v_draft2 = json::to_bjdata(j, true, true, json::bjdata_version_t::draft2);
+
+    // encode using BJData draft3
+    auto v_draft3 = json::to_bjdata(j, true, true, json::bjdata_version_t::draft3);
+
+    std::cout << "draft2 size: " << v_draft2.size() << '\n'
+              << "draft3 size: " << v_draft3.size() << std::endl;
+}
@@ -0,0 +1,2 @@
+draft2 size: 4
+draft3 size: 6
@@ -0,0 +1,11 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<byte_container_with_subtype::container_type, std::vector<std::uint8_t>>::value
+              << std::endl;
+}
@@ -0,0 +1 @@
+true
@@ -0,0 +1,15 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;
+
+int main()
+{
+    byte_container_with_subtype c1({0xca, 0xfe});
+    byte_container_with_subtype c2({0xca, 0xfe});
+    byte_container_with_subtype c3({0xca, 0xfe}, 42);
+
+    std::cout << std::boolalpha
+              << "c1 == c2: " << (c1 == c2) << '\n'
+              << "c1 == c3: " << (c1 == c3) << std::endl;
+}
@@ -0,0 +1,2 @@
+c1 == c2: true
+c1 == c3: false
@@ -0,0 +1,15 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;
+
+int main()
+{
+    byte_container_with_subtype c1({0xca, 0xfe});
+    byte_container_with_subtype c2({0xca, 0xfe});
+    byte_container_with_subtype c3({0xca, 0xfe}, 42);
+
+    std::cout << std::boolalpha
+              << "c1 != c2: " << (c1 != c2) << '\n'
+              << "c1 != c3: " << (c1 != c3) << std::endl;
+}
@@ -0,0 +1,2 @@
+c1 != c2: false
+c1 != c3: true
@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<byte_container_with_subtype::subtype_type, std::uint64_t>::value << std::endl;
+}
@@ -0,0 +1 @@
+true
@@ -0,0 +1,13 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // an initializer_list_t is what a braced-init-list of JSON values is deduced as
+    json::initializer_list_t init = {"a", 1, 2.0, false};
+
+    json j(init);
+    std::cout << j.dump() << std::endl;
+}
@@ -0,0 +1 @@
+["a",1,2.0,false]
@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::binary_t, json::binary_t>::value << std::endl;
+}
@@ -0,0 +1 @@
+true
@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::number_float_t, json::number_float_t>::value << std::endl;
+}
@@ -0,0 +1 @@
+true
@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::number_integer_t, json::number_integer_t>::value << std::endl;
+}
@@ -0,0 +1 @@
+true
@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::number_unsigned_t, json::number_unsigned_t>::value << std::endl;
+}
@@ -0,0 +1 @@
+true
@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t::string_t, json::string_t>::value << std::endl;
+}
@@ -0,0 +1 @@
+true
@@ -0,0 +1,10 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    std::cout << std::boolalpha
+              << std::is_same<json::json_sax_t, nlohmann::json_sax<json>>::value << std::endl;
+}
@@ -0,0 +1 @@
+true
@@ -0,0 +1,12 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    using Map = nlohmann::ordered_map<std::string, int>;
+
+    std::cout << std::boolalpha
+              << "Container is std::vector<std::pair<const Key, T>>: "
+              << std::is_same<Map::Container, std::vector<std::pair<const std::string, int>>>::value
+              << std::endl;
+}
@@ -0,0 +1 @@
+Container is std::vector<std::pair<const Key, T>>: true
@@ -0,0 +1,26 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+    m["one"] = 1;
+    m["two"] = 2;
+
+    // access an existing element
+    std::cout << "m.at(\"one\") = " << m.at("one") << std::endl;
+
+    // modify through the reference returned by at()
+    m.at("two") = 22;
+    std::cout << "m.at(\"two\") = " << m.at("two") << std::endl;
+
+    // accessing a missing key throws
+    try
+    {
+        m.at("three");
+    }
+    catch (const std::out_of_range& e)
+    {
+        std::cout << "exception: " << e.what() << std::endl;
+    }
+}
@@ -0,0 +1,3 @@
+m.at("one") = 1
+m.at("two") = 22
+exception: key not found
@@ -0,0 +1,12 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+    m["one"] = 1;
+
+    std::cout << std::boolalpha
+              << "m.count(\"one\") = " << m.count("one") << '\n'
+              << "m.count(\"two\") = " << m.count("two") << std::endl;
+}
@@ -0,0 +1,2 @@
+m.count("one") = 1
+m.count("two") = 0
@@ -0,0 +1,15 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, std::string> m;
+
+    // emplace a new element
+    auto res1 = m.emplace("one", "eins");
+    std::cout << std::boolalpha << "inserted: " << res1.second << ", value: " << res1.first->second << std::endl;
+
+    // emplace with an already-existing key: no-op, returns the existing element
+    auto res2 = m.emplace("one", "uno");
+    std::cout << std::boolalpha << "inserted: " << res2.second << ", value: " << res2.first->second << std::endl;
+}
@@ -0,0 +1,2 @@
+inserted: true, value: eins
+inserted: false, value: eins
@@ -0,0 +1,24 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+    m["one"] = 1;
+    m["two"] = 2;
+    m["three"] = 3;
+
+    // erase by key
+    std::size_t removed = m.erase("two");
+    std::cout << "removed by key: " << removed << std::endl;
+
+    // erase by iterator
+    m.erase(m.begin());
+
+    std::cout << "remaining: ";
+    for (const auto& element : m)
+    {
+        std::cout << element.first << ' ';
+    }
+    std::cout << std::endl;
+}
@@ -0,0 +1,2 @@
+removed by key: 1
+remaining: three 
@@ -0,0 +1,19 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+    m["one"] = 1;
+
+    auto it = m.find("one");
+    if (it != m.end())
+    {
+        std::cout << "found: " << it->first << " = " << it->second << std::endl;
+    }
+
+    if (m.find("two") == m.end())
+    {
+        std::cout << "\"two\" not found" << std::endl;
+    }
+}
@@ -0,0 +1,2 @@
+found: one = 1
+"two" not found
@@ -0,0 +1,21 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+
+    // insert a single value
+    auto res = m.insert({"one", 1});
+    std::cout << std::boolalpha << "inserted: " << res.second << std::endl;
+
+    // insert a range from another container
+    std::vector<std::pair<const std::string, int>> more = {{"two", 2}, {"three", 3}};
+    m.insert(more.begin(), more.end());
+
+    for (const auto& element : m)
+    {
+        std::cout << element.first << ':' << element.second << ' ';
+    }
+    std::cout << std::endl;
+}
@@ -0,0 +1,2 @@
+inserted: true
+one:1 two:2 three:3 
@@ -0,0 +1,12 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    using Map = nlohmann::ordered_map<std::string, int>;
+    Map::key_compare compare{};
+
+    std::cout << std::boolalpha
+              << "compare(\"a\", \"a\") = " << compare("a", "a") << '\n'
+              << "compare(\"a\", \"b\") = " << compare("a", "b") << std::endl;
+}
@@ -0,0 +1,2 @@
+compare("a", "a") = true
+compare("a", "b") = false
@@ -0,0 +1,14 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+int main()
+{
+    nlohmann::ordered_map<std::string, int> m;
+
+    // operator[] inserts a default-constructed value if the key doesn't exist yet
+    m["one"] = 1;
+    std::cout << "m[\"one\"] = " << m["one"] << std::endl;
+
+    // accessing again just returns the existing value
+    std::cout << "m[\"one\"] = " << m["one"] << std::endl;
+}
@@ -0,0 +1,2 @@
+m["one"] = 1
+m["one"] = 1
@@ -63,12 +63,6 @@ The library uses the following mapping from JSON values types to BJData types ac

      - strings with more than 18446744073709551615 bytes, i.e., $2^{64}-1$ bytes (theoretical)

-!!! warning "UTF-8 validation of string values and object keys"
-
-    BJData strings must use UTF-8 encoding. `to_bjdata()` validates the bytes of every string value and object key
-    and throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8, so a
-    value with such a string cannot be serialized in the first place.
-
 !!! info "Unused BJData markers"

    The following markers are not used in the conversion:
@@ -214,13 +208,6 @@ The library maps BJData types to JSON value types as follows:

    The mapping is **complete** in the sense that any BJData value can be converted to a JSON value.

-!!! warning "UTF-8 validation of string values and object keys"
-
-    This library validates the bytes of every string value and object key at decode time and rejects ill-formed
-    UTF-8 with a [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with
-    `allow_exceptions` set to `false`, a discarded value), rather than only failing later when the resulting value
-    is dumped.
-
 !!! info "Round trips"

    A value returned by [`from_bjdata`](../../api/basic_json/from_bjdata.md) can be serialized with
@@ -115,12 +115,8 @@ The library maps BSON record types to JSON value types as follows:
    bytes of every such string at decode time and rejects ill-formed UTF-8 with a
    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with `allow_exceptions`
    set to `false`, a discarded value), rather than only failing later when the resulting value is dumped. Element
-    (key) names and `binary` values (type `0x05`) are unaffected and are never validated on read, since they are read
-    byte-by-byte as a C string, or are not required to hold text, respectively. `to_bson()` validates both string
-    values and element names and throws
-    [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8 in either, so an
-    object with such a key or value cannot be produced in the first place, even though `from_bson()` would accept it
-    from another source.
+    (key) names and `binary` values (type `0x05`) are unaffected and are never validated, since they are read
+    byte-by-byte as a C string, or are not required to hold text, respectively.

 ??? example

@@ -197,9 +197,7 @@ The library maps CBOR types to JSON value types as follows:
    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with
    `allow_exceptions` set to `false`, a discarded value), rather than only failing later when the resulting value is
    dumped. Byte strings (major type 2) are unaffected and are never validated, since they are not required to hold
-    text. `to_cbor()` validates string values and object keys the same way and throws
-    [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8, so a value with
-    such a string cannot be serialized in the first place.
+    text.

 !!! warning "Tagged items"

@@ -153,15 +153,14 @@ The library maps MessagePack types to JSON value types as follows:
    This applies to the [SAX interface](../parsing/sax_interface.md) as well, as the key is read before it is passed
    on. Such input needs a general-purpose MessagePack library instead.

-!!! warning "Ill-formed UTF-8 in string values"
+!!! warning "UTF-8 validation of string values"

-    The MessagePack specification explicitly allows a `str` value (`fixstr`, `str 8`, `str 16`, `str 32`) to contain
-    a byte sequence that is not valid UTF-8, and expects a deserializer to hand the original bytes back unchanged.
-    This library follows that: `from_msgpack()` reads `str` bytes (object keys included) as-is, without validating
-    them, and `to_msgpack()` writes them back as-is, so such a value round-trips through `from_msgpack(to_msgpack(j))`
-    byte for byte. However, [`dump()`](../../api/basic_json/dump.md) still requires valid UTF-8 and throws
-    [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a value read this way, unless an
-    error handler is passed that replaces or ignores the ill-formed bytes.
+    The MessagePack specification requires `str` values (`fixstr`, `str 8`, `str 16`, `str 32`) to be valid UTF-8.
+    This library validates the bytes of every such string (object keys included) at decode time and rejects
+    ill-formed UTF-8 with a [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or,
+    with `allow_exceptions` set to `false`, a discarded value), rather than only failing later when the resulting
+    value is dumped. `bin`/`ext`/`fixext` values are unaffected and are never validated, since they are not required
+    to hold text.

 ??? example

@@ -47,12 +47,6 @@ The library uses the following mapping from JSON values types to UBJSON types ac

      - strings with more than 9223372036854775807 bytes (theoretical)

-!!! warning "UTF-8 validation of string values and object keys"
-
-    UBJSON's required string encoding is UTF-8. `to_ubjson()` validates the bytes of every string value and object
-    key and throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8, so
-    a value with such a string cannot be serialized in the first place.
-
 !!! info "Unused UBJSON markers"

    The following markers are not used in the conversion:
@@ -126,13 +120,6 @@ The library maps UBJSON types to JSON value types as follows:

    The mapping is **complete** in the sense that any UBJSON value can be converted to a JSON value.

-!!! warning "UTF-8 validation of string values and object keys"
-
-    This library validates the bytes of every string value and object key at decode time and rejects ill-formed
-    UTF-8 with a [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with
-    `allow_exceptions` set to `false`, a discarded value), rather than only failing later when the resulting value
-    is dumped.
-
 ??? example

    ```cpp
@@ -83,13 +83,6 @@ When defined, default parse and serialize functions for enums are excluded and h

 See [full documentation of `JSON_DISABLE_ENUM_SERIALIZATION`](../api/macros/json_disable_enum_serialization.md).

-## `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`
-
-When defined to `1`, a JSON value can no longer be created from a one-element `std::tuple` holding a reference to a JSON
-value, such as the result of `std::forward_as_tuple(j)`. This lets `std::tuple` convert such tuples element-wise.
-
-See [full documentation of `JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../api/macros/json_disable_tuple_reference_conversion.md).
-
 ## `JSON_NO_AUTOMATIC_UDLS`

 When defined, `<nlohmann/json.hpp>` does not include `<nlohmann/json_literals.hpp>` with the user-defined string literals
@@ -51,16 +51,16 @@ If you do want to preserve the **insertion order**, you can use the type [`nlohm
    --8<-- "examples/ordered_json.output"
    ```

-Alternatively, [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) also preserves the insertion order and, unlike [`ordered_map`](../api/ordered_map.md), keeps a lookup index, so it does not have the quadratic cost described below. It is used through a small adapter ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).
+Alternatively, [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) also preserves the insertion order and, unlike [`ordered_map`](../api/ordered_map/index.md), keeps a lookup index, so it does not have the quadratic cost described below. It is used through a small adapter ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).

 If the order does not matter and you only want faster lookup, `boost::unordered_flat_map`, `absl::flat_hash_map`, `absl::node_hash_map`, and several other hash maps work through an adapter that restores the template argument order `basic_json` expects; see [Template Parameter Requirements](types/template_parameters.md#objecttype). Note these are *unordered*, not insertion-ordered.

 [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) cannot be used: its iterators expose the mapped value as `const`, while `basic_json` needs to modify it in place.

-The [`ordered_map`](../api/ordered_map.md) behind `nlohmann::ordered_json` is deliberately minimal and has no lookup
+The [`ordered_map`](../api/ordered_map/index.md) behind `nlohmann::ordered_json` is deliberately minimal and has no lookup
 index, so every key access is a linear scan and building an object of `n` keys costs O(n²). This is unnoticeable at
 typical object sizes but becomes significant for objects with many thousands of keys; see
-[`ordered_map` complexity](../api/ordered_map.md#complexity). The alternatives above keep a lookup index and do not
+[`ordered_map` complexity](../api/ordered_map/index.md#complexity). The alternatives above keep a lookup index and do not
 have this cost.

 ### Notes on parsing
@@ -37,7 +37,7 @@ Requirements are split into two groups:

 | Template parameter                                                | Default                           | Notable substitutes                                                   |
 |-------------------------------------------------------------------|-----------------------------------|-----------------------------------------------------------------------|
-| [`ObjectType`](#objecttype)                                       | `std::map`                        | [`nlohmann::ordered_map`](../../api/ordered_map.md), Abseil hash maps |
+| [`ObjectType`](#objecttype)                                       | `std::map`                        | [`nlohmann::ordered_map`](../../api/ordered_map/index.md), Abseil hash maps |
 | [`ArrayType`](#arraytype)                                         | `std::vector`                     | `#!cpp std::deque`                                                    |
 | [`StringType`](#stringtype)                                       | `std::string`                     | `std::string`-like types over `char`                                  |
 | [`BooleanType`](#booleantype)                                     | `bool`                            | none worth using                                                      |
@@ -230,7 +230,7 @@ The library does not sort or de-duplicate keys itself; the behavior described in
 | Container                                                                        | Notes                                                                         |
 |----------------------------------------------------------------------------------|-------------------------------------------------------------------------------|
 | `#!cpp std::map` (default)                                                       |                                                                               |
-| [`nlohmann::ordered_map`](../../api/ordered_map.md)                              | used by [`ordered_json`](../../api/ordered_json.md); keeps insertion order    |
+| [`nlohmann::ordered_map`](../../api/ordered_map/index.md)                              | used by [`ordered_json`](../../api/ordered_json.md); keeps insertion order    |
 | [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map)                     | keeps insertion order; adapter puts `fifo_map_compare` in the comparator slot |
 | `boost::container::map`, `boost::container::flat_map`                            | no adapter needed                                                             |
 | `#!cpp std::unordered_map`                                                       | through the adapter above; not with libstdc++ 9, see the note                 |
@@ -50,7 +50,7 @@ The public headers are in [`include/nlohmann`](https://github.com/nlohmann/json/
 - [`adl_serializer.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/adl_serializer.hpp), [`byte_container_with_subtype.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/byte_container_with_subtype.hpp), and [`ordered_map.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/ordered_map.hpp) define
  [`adl_serializer`](../api/adl_serializer/index.md),
  [`byte_container_with_subtype`](../api/byte_container_with_subtype/index.md), and
-  [`ordered_map`](../api/ordered_map.md).
+  [`ordered_map`](../api/ordered_map/index.md).

 Everything else lives in [`detail/`](https://github.com/nlohmann/json/tree/develop/include/nlohmann/detail) and namespace `nlohmann::detail`, which is not part of the public API. Paths
 below are relative to `include/nlohmann`.
@@ -97,7 +97,7 @@ is generated from these files with `make amalgamate` and must not be edited by h
 The library provides two specializations:

 - [`json`](../api/json.md) uses all default template arguments.
- [`ordered_json`](../api/ordered_json.md) uses [`ordered_map`](../api/ordered_map.md) as `ObjectType` to keep the
+- [`ordered_json`](../api/ordered_json.md) uses [`ordered_map`](../api/ordered_map/index.md) as `ObjectType` to keep the
  insertion order of object keys.

 The requirements on the template arguments are listed in
@@ -2,7 +2,8 @@

 This page summarizes the notable changes of every release and links to the relevant documentation.
 The **complete release notes** — including all changes, the download files, and their checksums — are
-published on the [GitHub releases page](https://github.com/nlohmann/json/releases).
+published on the [GitHub releases page](https://github.com/nlohmann/json/releases). For a raw,
+signature-level diff of the public API between releases, see [API Changes](api_changes.md).

 ## v3.12.0 (2025-04-11)

@@ -169,12 +169,6 @@ Enable position diagnostics by defining macro [`JSON_DIAGNOSTIC_POSITIONS`](../a
 Disable default `enum` serialization by defining the macro
 [`JSON_DISABLE_ENUM_SERIALIZATION`](../api/macros/json_disable_enum_serialization.md). This option is `OFF` by default.

-### `JSON_DisableTupleReferenceConversion`
-
-Disable the conversion from a one-element `std::tuple` holding a reference to a JSON value by defining the macro
-[`JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../api/macros/json_disable_tuple_reference_conversion.md). This option is
-`OFF` by default.
-
 ### `JSON_FastTests`

 Skip expensive/slow test suites. This option is `OFF` by default. Depends on `JSON_BuildTests`.
@@ -52,6 +52,7 @@ nav:
      - "FAQ": home/faq.md
      - home/exceptions.md
      - home/releases.md
+      - home/api_changes.md
      - home/design_goals.md
      - home/architecture.md
      - home/customers.md
@@ -119,6 +120,7 @@ nav:
          - 'begin': api/basic_json/begin.md
          - 'binary': api/basic_json/binary.md
          - 'binary_t': api/basic_json/binary_t.md
+          - 'bjdata_version_t': api/basic_json/bjdata_version_t.md
          - 'boolean_t': api/basic_json/boolean_t.md
          - 'cbegin': api/basic_json/cbegin.md
          - 'cbor_tag_handler_t': api/basic_json/cbor_tag_handler_t.md
@@ -157,6 +159,7 @@ nav:
          - 'get_to': api/basic_json/get_to.md
          - 'std::formatter&lt;basic_json&gt;': api/basic_json/std_formatter.md
          - 'std::hash&lt;basic_json&gt;': api/basic_json/std_hash.md
+          - 'initializer_list_t': api/basic_json/initializer_list_t.md
          - 'input_format_t': api/basic_json/input_format_t.md
          - 'insert': api/basic_json/insert.md
          - 'invalid_iterator': api/basic_json/invalid_iterator.md
@@ -175,6 +178,7 @@ nav:
          - 'is_structured': api/basic_json/is_structured.md
          - 'items': api/basic_json/items.md
          - 'json_base_class_t': api/basic_json/json_base_class_t.md
+          - 'json_sax_t': api/basic_json/json_sax_t.md
          - 'json_serializer': api/basic_json/json_serializer.md
          - 'max_size': api/basic_json/max_size.md
          - 'meta': api/basic_json/meta.md
@@ -232,9 +236,13 @@ nav:
          - 'Overview': api/byte_container_with_subtype/index.md
          - '(constructor)': api/byte_container_with_subtype/byte_container_with_subtype.md
          - 'clear_subtype': api/byte_container_with_subtype/clear_subtype.md
+          - 'container_type': api/byte_container_with_subtype/container_type.md
          - 'has_subtype': api/byte_container_with_subtype/has_subtype.md
+          - 'operator==': api/byte_container_with_subtype/operator_eq.md
+          - 'operator!=': api/byte_container_with_subtype/operator_ne.md
          - 'set_subtype': api/byte_container_with_subtype/set_subtype.md
          - 'subtype': api/byte_container_with_subtype/subtype.md
+          - 'subtype_type': api/byte_container_with_subtype/subtype_type.md
      - adl_serializer:
          - 'Overview': api/adl_serializer/index.md
          - 'from_json': api/adl_serializer/from_json.md
@@ -260,25 +268,46 @@ nav:
          - 'to_string': api/json_pointer/to_string.md
      - json_sax:
          - 'Overview': api/json_sax/index.md
+          - '(Constructor)': api/json_sax/json_sax.md
+          - '(Destructor)': api/json_sax/~json_sax.md
+          - 'operator=': api/json_sax/operator=.md
          - 'binary': api/json_sax/binary.md
+          - 'binary_t': api/json_sax/binary_t.md
          - 'boolean': api/json_sax/boolean.md
          - 'end_array': api/json_sax/end_array.md
          - 'end_object': api/json_sax/end_object.md
          - 'key': api/json_sax/key.md
          - 'null': api/json_sax/null.md
          - 'number_float': api/json_sax/number_float.md
+          - 'number_float_t': api/json_sax/number_float_t.md
          - 'number_integer': api/json_sax/number_integer.md
+          - 'number_integer_t': api/json_sax/number_integer_t.md
          - 'number_unsigned': api/json_sax/number_unsigned.md
+          - 'number_unsigned_t': api/json_sax/number_unsigned_t.md
          - 'parse_error': api/json_sax/parse_error.md
          - 'start_array': api/json_sax/start_array.md
          - 'start_object': api/json_sax/start_object.md
          - 'string': api/json_sax/string.md
+          - 'string_t': api/json_sax/string_t.md
      - 'operator<<(basic_json), operator<<(json_pointer)': api/operator_ltlt.md
      - 'operator>>(basic_json)': api/operator_gtgt.md
      - 'operator""_json': api/operator_literal_json.md
      - 'operator""_json_pointer': api/operator_literal_json_pointer.md
      - 'ordered_json': api/ordered_json.md
-      - 'ordered_map': api/ordered_map.md
+      - ordered_map:
+          - 'Overview': api/ordered_map/index.md
+          - '(Constructor)': api/ordered_map/ordered_map.md
+          - '(Destructor)': api/ordered_map/~ordered_map.md
+          - 'operator=': api/ordered_map/operator=.md
+          - 'at': api/ordered_map/at.md
+          - 'Container': api/ordered_map/Container.md
+          - 'count': api/ordered_map/count.md
+          - 'emplace': api/ordered_map/emplace.md
+          - 'erase': api/ordered_map/erase.md
+          - 'find': api/ordered_map/find.md
+          - 'insert': api/ordered_map/insert.md
+          - 'key_compare': api/ordered_map/key_compare.md
+          - 'operator[]': api/ordered_map/operator[].md
      - macros:
          - 'Overview': api/macros/index.md
          - 'JSON_ASSERT': api/macros/json_assert.md
@@ -287,7 +316,6 @@ nav:
          - 'JSON_DIAGNOSTICS': api/macros/json_diagnostics.md
          - 'JSON_DIAGNOSTIC_POSITIONS': api/macros/json_diagnostic_positions.md
          - 'JSON_DISABLE_ENUM_SERIALIZATION': api/macros/json_disable_enum_serialization.md
-          - 'JSON_DISABLE_TUPLE_REFERENCE_CONVERSION': api/macros/json_disable_tuple_reference_conversion.md
          - 'JSON_HAS_CPP_11, JSON_HAS_CPP_14, JSON_HAS_CPP_17, JSON_HAS_CPP_20': api/macros/json_has_cpp_11.md
          - 'JSON_HAS_EXPERIMENTAL_FILESYSTEM, JSON_HAS_FILESYSTEM': api/macros/json_has_filesystem.md
          - 'JSON_HAS_RANGES': api/macros/json_has_ranges.md
--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
Niels Lohmann	9196e92520	Merge branch 'develop' into claude/todo-191-plan-508110 Conflicts: none textual. Follow-up fixes for develop's changes: - docs/mkdocs/docs/api/ordered_map/index.md: develop's new paragraph (#5609) was written for api/ordered_map.md; fixed its relative ordered_json.md link for the page's new location, plus two pre-existing links from an earlier merge (ordered_json.md, features/object_order.md) - tools/api_checker/api_surface.json: regenerated with libclang 18.1.1 on Linux (swap() noexcept now includes json_base_class_t; new integral-key contains/count/find/value overloads) Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-30 20:36:12 +02:00
Niels Lohmann	7d22d865dd	Merge branch 'develop' into claude/todo-191-plan-508110 Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-28 22:22:46 +02:00
Niels Lohmann	4c73319d3b	Use one-line module docstrings in the API checker scripts Codacy runs two docstring checkers with opposite rules for module docstrings: with the summary on the first line it reported D213, with the summary on the second line it reports D212. A one-line docstring satisfies both. Keep the summary as the docstring and move the details into a comment below it; nothing reads the module docstrings. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-28 18:42:34 +02:00
Niels Lohmann	da5097abcd	Restore the CI spelling of json_pointer's operator string_t in the API surface The develop merge regenerated api_surface.json on macOS, whose libclang spells the name of the deprecated conversion operator as "operator nlohmann::json_pointer::string_t_helper<...>::type". CI's pinned libclang 18.1.1 on Linux spells it "operator typename string_t_helper<...>::type", so check_api_docs reported the file as out of date. This restores CI's spelling, which is byte-identical to the file CI regenerated. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-27 21:37:14 +02:00
Niels Lohmann	2319f6e6f9	Address Codacy findings in the API checker scripts Put multi-line docstring summaries on their own line, as a single sentence followed by a blank line (pydocstyle D205, D209, D213, D415). Annotate the subprocess import and calls with nosec: they only run fixed argument lists, never through a shell (Bandit B404, B603, B607). Do the same for the three broad except clauses in extract_api.py, which deliberately fall through to the next libclang candidate or skip an unresolvable alias (Bandit B110, B112). Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-27 18:09:03 +02:00
Niels Lohmann	9a0d1c0c47	Merge branch 'develop' into claude/todo-191-plan-508110 Resolve the conflict in docs/mkdocs/docs/home/architecture.md by taking develop's rewritten page and pointing its ordered_map links at the moved api/ordered_map/index.md. Also update the ordered_map.md links develop added in ordered_json.md, object_order.md, and template_parameters.md. Regenerate api_surface.json for the new BON8 functions and the changed comparison operator. Restrict the documented_non_public leak check to @sa URLs into json.nlohmann.me: develop now uses @sa to link GitHub issues from private members such as copy_structured, which is not a documentation leak. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-27 18:07:00 +02:00
Niels Lohmann	1bbb5d400a	Regenerate api_surface.json after merging develop develop added JSON_HEDLEY_WARN_UNUSED_RESULT to a number of basic_json members (#5520) and reworked operator<<'s output adapter, so the committed API surface no longer matched what extract_api.py produces and the "Check for uncommitted API surface changes" step failed. This is the patch the workflow itself uploads for that purpose; the changes are limited to recorded signatures plus the way libclang spells json_pointer's conversion operator. Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-09-15 10:06:55 +02:00
Niels Lohmann	08d18d5a82	Merge remote-tracking branch 'origin/develop' into HEAD	2026-09-14 21:26:29 +02:00
Niels LohmannandClaude Sonnet 5	a27065bd12	Regenerate api_surface.json after merging develop develop gained iterator+sentinel support for accept()/parse()/sax_parse()/ from_cbor()/from_msgpack()/from_ubjson()/from_bjdata()/from_bson() (#5205) since this branch was created, which check_api_docs.yml's drift check caught immediately: GitHub's pull_request trigger checks out the PR-vs-base merge commit, not the PR branch in isolation, so CI was comparing the committed api_surface.json (generated before that upstream change existed) against a fresh extraction of a json.hpp that already had it. This superseded an earlier, incorrect diagnosis of the same symptom (a JSON_HAS_RANGES cross-environment pin) -- that fix remains in place since it's still a real, independent determinism improvement for three other JSON_HAS_RANGES-gated locations in type_traits.hpp, but it wasn't the actual cause of this particular mismatch: these new overloads turned out to be unconditional (SFINAE-gated via can_compare_ne, not preprocessor-gated), so no environment-detection difference was involved here at all. Signed-off-by: Niels Lohmann <mail@nlohmann.me> Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-07-11 23:45:46 +02:00
Niels Lohmann	3940f4b730	Merge remote-tracking branch 'origin/develop' into claude/todo-191-plan-508110	2026-07-11 23:43:30 +02:00
Niels LohmannandClaude Sonnet 5	0663907b68	Fix cross-environment API-surface drift and lint findings from CI extract_api.py's own extraction wasn't deterministic across machines, which CI's drift check caught immediately: JSON_HAS_RANGES auto-detects via the standard library's __cpp_lib_ranges feature-test macro, which isn't reliably gated to C++20 mode by every stdlib -- undefined under -std=c++17 with macOS's libc++, but defined under the identical flag with the Ubuntu stdlib CI uses, so parse()/accept()/from_*() extracted different signatures purely depending on which machine ran the extraction. Pinned to -DJSON_HAS_RANGES=0: the deterministic and safe choice, since pinning to 1 was tried first and found to fail to parse on a stdlib without full <ranges> support even when the macro claims otherwise. Also found and fixed a second, independent source of the same class of drift: get_identity_name() used cursor.spelling verbatim for CONVERSION_FUNCTION cursors, which libclang renders as its own internally-canonicalized form of the return type rather than what's literally written. Confirmed for json_pointer::operator string_t() spelling differently on two machines pinned to the identical libclang==18.1.1 wheel, with the JSON_HAS_RANGES fix above ruled out as the cause. Now derived from the cursor's own raw source text instead, immune to libclang's dependent-type resolution differences and incidentally more readable than the libclang-internal forms it replaces. Bumped SURFACE_FORMAT_VERSION to 3 and regenerated all 27 history snapshots and the committed api_surface.json; both fixes are documented in tools/api_checker/history/README.md's format-history log. Also fixes diff_api.py's format_version guard, which only compared the two loaded surfaces against each other and never against SURFACE_FORMAT_VERSION (what this build actually understands) -- two surfaces on the same, newer-than-expected format_version would have silently passed the guard. Remaining fixes are the concretely actionable findings from Codacy's review of the new tools/api_checker/ files: unused imports/variables, a stray f-string with no placeholders. Left the docstring-formatting nitpicks (pydocstyle D2xx/D4xx) and generic subprocess-usage notices alone -- the former has no established convention elsewhere in this codebase's Python tooling to conform to, and the latter are inherent to a dev tool that shells out to git/clang with developer-controlled arguments, not user input. Signed-off-by: Niels Lohmann <mail@nlohmann.me> Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-07-11 18:59:19 +02:00
Niels LohmannandClaude Sonnet 5	f23b3c63a2	Add AST-based public API checker and fix documentation gaps it found (#3691 ) Adds tools/api_checker/: extract_api.py derives the public API surface directly from the libclang AST (independent of documentation status), check_docs.py flags public entries missing @sa links (and @sa on non-public ones), diff_api.py does an overload-aware breaking/feature diff between two refs, check_macros.py cross- checks documented macros against #define sites, and snapshot_release.py backfills immutable per-release surface snapshots into tools/api_checker/history/ (v3.1.0 through v3.12.0) so diff_api.py can compare releases without live extraction. POLICY.md documents what counts as public API and what stability is guaranteed. Running this tooling against the current tree found and fixed a real documentation backlog: ~25 new API doc pages (ordered_map's methods, json_sax's ctor/dtor/ operator=, byte_container_with_subtype's comparison operators, several orphaned type aliases), each with a compiled and output-verified example, plus missing @sa comments and stale/incorrect Version History entries on several existing pages (found by diffing consecutive release pairs and checking whether the resulting change was actually reflected in the target page's history section). Also adds docs/home/api_changes.md, a per-release, per-function reference of public API changes (v3.1.0 through v3.12.0) generated from the history/ snapshots, complementing (not replacing) the existing release notes. Along the way, found and fixed several extractor bugs by testing against real release tags rather than trusting the algorithm in isolation -- most notably an identity-key scheme based on libclang's USR that encoded the enclosing class template's own arity, and a since-renamed ABI inline-namespace pattern (json_v3_11_0 vs. today's json_abi_v3_11_2) that neither of two earlier regex attempts stripped correctly. Both are documented in extract_api.py's docstrings and tools/api_checker/history/README.md so the failure mode doesn't recur silently. .github/workflows/check_api_docs.yml runs extract_api.py + check_docs.py in CI, advisory-only for now (documented backlog may not be at zero for entities this PR didn't touch), plus a blocking drift check on the committed tools/api_checker/api_surface.json. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Signed-off-by: Niels Lohmann <mail@nlohmann.me>	2026-07-11 18:59:00 +02:00
				`@@ -0,0 +1 @@`
				`Container is std::vector<std::pair<const Key, T>>: true`