Redesign the iterative binary writers around a shared recursion depth limit

Address the open review on the non-recursive CBOR/MessagePack/UBJSON/BJData writers (#5518): - Delete the CBOR array/object prefix helpers; both the recursive and iterative paths call write_cbor_head(), which already existed on develop. - MessagePack: share one write_msgpack_array_prefix()/write_msgpack_object_prefix() helper per container kind between the recursive and iterative paths, both going through to_msgpack_length() so an over-long container throws out_of_range.412 identically either way. - Reuse detail::recursion_depth_limit() instead of a separate constant, the same bound serializer::dump() and write_bson_document() already use. - Redesign the frames after bson_frame/dump_frame: only a container with elements is ever pushed, its header is written at the point it is pushed, and the iterator is set in the frame's constructor instead of a default-then-assign two-step with a since-removed "started" flag. The UBJSON frame keeps only the value pointer, the per-element prefix_required flag, and the iterator; write_closer and is_object are no longer stored, since the former is always !use_count (use_count is constant for the whole document) and the latter follows from value->is_object(). - Factor the BJData ND-array shape check into is_bjdata_ndarray(), used by both the recursive object case and the iterative pushing logic. - Give the frame classes the GCC -Weffc++ treatment already used for diff_frame: a noexcept converting constructor plus the five special members defaulted with no explicit noexcept. - Fix two @ref self-references in write_cbor/write_msgpack/write_ubjson's own doc comments to point at the public to_cbor/to_msgpack/to_ubjson/to_bjdata API instead. - The iterative object-key write for CBOR/MessagePack now runs the same strict-mode check_utf8() against the parent object as diagnostics context that the recursive path already ran, so the two paths raise identical diagnostics across the switch-over. - Rewrite the tests: round trips instead of a bare size check, byte-exact comparisons against the recursive output at depths around the bound, a deep object and a BJData ND-array past the bound, a deep discarded value (type_error.321), and the OSS-Fuzz 566583014 CBOR/MessagePack regression. BSON is unaffected by this change; it already walks its documents iteratively and is covered separately by #5553. Co-authored-by: ayush-singh-0601 <179524189+ayush-singh-0601@users.noreply.github.com> Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Stop binary writers overflowing the stack on deep values
2026-10-07 15:07:13 +00:00 · 2026-10-07 16:40:07 +02:00 · 2026-10-07 16:40:04 +02:00 · 2026-10-07 16:37:19 +02:00 · 2026-10-07 09:03:18 +02:00 · 2026-10-07 09:03:17 +02:00
236 changed files with 16950 additions and 76126 deletions
@@ -205,6 +205,9 @@ API of the 3.x.y version is broken. This includes:
 - Changing access specifiers.
 - Changing default arguments.

+What is and is not covered by this guarantee is described in the
+[roadmap](https://json.nlohmann.me/community/roadmap/#api-stability).
+
 Although these guidelines may seem restrictive, they are essential for maintaining the library’s utility.

 Breaking changes may be introduced when they are guarded with a feature macro such as
@@ -16,6 +16,9 @@ only_commits:

 environment:
  matrix:
+    # The Visual Studio 2017 jobs compile everything with /std:c++17, so they
+    # only build the C++17 variant of each test, split into two jobs each to
+    # stay below AppVeyor's 60-minute limit per job.
    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
      configuration: Debug
      platform: x86
@@ -34,7 +37,13 @@ environment:
      configuration: Release
      platform: x86
      CXX_FLAGS: "/permissive- /std:c++17 /utf-8 /W4 /WX"
-      CMAKE_OPTIONS: ""
+      CMAKE_OPTIONS: "-DJSON_TestStandards=17 -DJSON_TestShard=0/2"
+      GENERATOR: Visual Studio 15 2017
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      configuration: Release
+      platform: x86
+      CXX_FLAGS: "/permissive- /std:c++17 /utf-8 /W4 /WX"
+      CMAKE_OPTIONS: "-DJSON_TestStandards=17 -DJSON_TestShard=1/2"
      GENERATOR: Visual Studio 15 2017

    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
@@ -55,7 +64,13 @@ environment:
      configuration: Release
      platform: x64
      CXX_FLAGS: "/permissive- /std:c++17 /Zc:__cplusplus /utf-8 /W4 /WX"
-      CMAKE_OPTIONS: ""
+      CMAKE_OPTIONS: "-DJSON_TestStandards=17 -DJSON_TestShard=0/2"
+      GENERATOR: Visual Studio 15 2017
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      configuration: Release
+      platform: x64
+      CXX_FLAGS: "/permissive- /std:c++17 /Zc:__cplusplus /utf-8 /W4 /WX"
+      CMAKE_OPTIONS: "-DJSON_TestStandards=17 -DJSON_TestShard=1/2"
      GENERATOR: Visual Studio 15 2017

 init:
@@ -66,15 +81,10 @@ install:
  - if "%platform%"=="x86"    set GENERATOR_PLATFORM=Win32

 before_build:
-  - cmake . -G "%GENERATOR%" -A "%GENERATOR_PLATFORM%" -DCMAKE_CXX_FLAGS="%CXX_FLAGS%" -DCMAKE_IGNORE_PATH="C:/Program Files/Git/usr/bin" -DJSON_BuildTests=On "%CMAKE_OPTIONS%"
+  - cmake . -G "%GENERATOR%" -A "%GENERATOR_PLATFORM%" -DCMAKE_CXX_FLAGS="%CXX_FLAGS%" -DCMAKE_IGNORE_PATH="C:/Program Files/Git/usr/bin" -DJSON_BuildTests=On %CMAKE_OPTIONS%

 build_script:
  - cmake --build . --config "%configuration%" --parallel 2

 test_script:
-  - if "%configuration%"=="Release" ctest -C "%configuration%" --parallel 2 --output-on-failure
-  # On Debug builds, skip test-unicode_all
-  # as it is extremely slow to run and cause
-  # occasional timeouts on AppVeyor.
-  # More info: https://github.com/nlohmann/json/pull/1570
-  - if "%configuration%"=="Debug" ctest --exclude-regex "test-unicode" -C "%configuration%" --parallel 2 --output-on-failure
+  - ctest -C "%configuration%" --parallel 2 --output-on-failure
@@ -1,81 +0,0 @@
-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
@@ -17,11 +17,11 @@ permissions:
  contents: read

 jobs:
-  macos-14:
-    runs-on: macos-14 # https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md
+  macos-15:
+    runs-on: macos-15 # https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
    strategy:
      matrix:
-        xcode: ['15.0.1', '15.1', '15.2', '15.3', '15.4']
+        xcode: ['16.0', '16.1', '16.2', '16.3', '16.4', '26.0.1', '26.1.1', '26.2', '26.3']
    env:
      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer

@@ -36,11 +36,11 @@ jobs:
      - name: Test
        run: cd build ; ctest -j 10 --output-on-failure

-  macos-15:
-    runs-on: macos-15 # https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
+  macos-26:
+    runs-on: macos-26 # https://github.com/actions/runner-images/blob/main/images/macos/macos-26-arm64-Readme.md
    strategy:
      matrix:
-        xcode: ['16.0', '16.1', '16.2', '16.3', '16.4', '26.0.1']
+        xcode: ['26.4.1', '26.5', '26.6']
    env:
      DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer

@@ -71,3 +71,38 @@ jobs:
        run: cmake --build build --parallel 10
      - name: Test
        run: cd build ; ctest -j 10 --output-on-failure
+
+  swiftpm:
+    runs-on: macos-15
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+      - name: Check that Package.swift resolves without a deprecation warning
+        run: swift package dump-package
+      - name: Build the SwiftPM documentation example against this checkout
+        run: |
+          mkdir -p /tmp/json-swiftpm-consumer/Sources/MyLibrary
+          cp docs/mkdocs/docs/integration/swift/example.cpp /tmp/json-swiftpm-consumer/Sources/MyLibrary/example.cpp
+          cat > /tmp/json-swiftpm-consumer/Package.swift << EOF
+          // swift-tools-version: 5.9
+          import PackageDescription
+
+          let package = Package(
+              name: "MyPackage",
+              dependencies: [
+                  .package(path: "${{ github.workspace }}")
+              ],
+              targets: [
+                  .target(
+                      name: "MyLibrary",
+                      dependencies: [
+                          .product(name: "json", package: "json")
+                      ],
+                      publicHeadersPath: "."
+                  )
+              ]
+          )
+          EOF
+          cd /tmp/json-swiftpm-consumer
+          swift build
@@ -107,7 +107,7 @@ jobs:
    container: ubuntu:24.04
    strategy:
      matrix:
-        target: [ci_cmake_flags, ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_noglobaludls, ci_test_disableenumserialization, ci_test_disabletuplereferenceconversion, ci_test_skiplibraryversioncheck, ci_test_simdutf, ci_test_strict_nul_handling, ci_test_no_thread_local]
+        target: [ci_cmake_flags, ci_test_diagnostics, ci_test_diagnostic_positions, ci_test_noexceptions, ci_test_noimplicitconversions, ci_test_legacycomparison, ci_test_noglobaludls, ci_test_disableenumserialization, ci_test_disabletuplereferenceconversion, ci_test_skiplibraryversioncheck, ci_test_simdutf, ci_test_strict_nul_handling, ci_test_delete_deprecated_functions, ci_test_no_thread_local]
    steps:
      - name: Install build-essential
        run: apt-get update ; apt-get install -y build-essential unzip wget git
@@ -209,7 +209,7 @@ jobs:
    strategy:
      matrix:
        # older GCC docker images (4, 5, 6) fail to check out code
-        compiler: ['7', '8', '9', '10', '11', '12', '13', '14', '15', 'latest']
+        compiler: ['7', '8', '9', '10', '11', '12', '13', '14', '15', '16', 'latest']
    container: gcc:${{ matrix.compiler }}
    steps:
      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -178,7 +178,7 @@ jobs:
      - name: Build
        run: cmake --build build --parallel 10
      - name: Test
-        run: cd build ; ctest -j 10 -C Debug --exclude-regex "test-unicode" --output-on-failure
+        run: cd build ; ctest -j 10 -C Debug --output-on-failure

  clang-cl-12:
    runs-on: windows-2022
@@ -195,7 +195,7 @@ jobs:
      - name: Build
        run: cmake --build build --config Debug --parallel 10
      - name: Test
-        run: cd build ; ctest -j 10 -C Debug --exclude-regex "test-unicode" --output-on-failure
+        run: cd build ; ctest -j 10 -C Debug --output-on-failure

  ci_module_cpp20:
    runs-on: windows-2022
@@ -3,7 +3,6 @@
 *.gcno
 *.gcda
 .DS_Store
-__pycache__/

 /.idea
 /cmake-build-*
@@ -46,9 +45,5 @@ 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
@@ -1,5 +1,7 @@
 {
  "_comment": "Used by the ci_infer CMake target (#5715 item 4b). fail-on-issue makes CI fail on Infer findings; disable-issue-type is a type-level baseline for the ~174 pre-existing findings (all PULSE_UNNECESSARY_COPY*/PULSE_RESOURCE_LEAK/PULSE_CONST_REFABLE, mostly in test code) triaged in run https://github.com/nlohmann/json/actions/runs/35829411620 on commit 1054b2097, so CI fails only on a NEW issue type. Remove an entry here once its findings have been fixed or explicitly accepted.",
+  "_comment_pulse": "Pulse stops exploring paths after pulse-max-disjuncts (default 20). With the default, basic_json::replace_value() (destroy + assert_invariant) exceeds the limit, Pulse loses the stored type, and reports false NULLPTR_DEREFERENCE findings for get_ptr() results in tests/src/unit-pointer_access.cpp.",
+  "pulse-max-disjuncts": 40,
  "fail-on-issue": true,
  "disable-issue-type": [
    "PULSE_UNNECESSARY_COPY_ASSIGNMENT",
@@ -1,36 +0,0 @@
-Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
-Upstream-Name: json
-Upstream-Contact: Niels Lohmann <mail@nlohmann.me>
-Source: https://github.com/nlohmann/json
-
-Files: *
-Copyright: 2013-2026 Niels Lohmann <https://nlohmann.me>
-License: MIT
-
-Files: include/nlohmann/thirdparty/hedley.hpp
-Copyright: 2016-2021 Evan Nemerson <evan@nemerson.com>
-License: CC0
-
-Files: include/nlohmann/detail/meta/cpp_future.hpp
-Copyright: 2013-2026 Niels Lohmann <https://nlohmann.me> and 2018 The Abseil Authors
-License: MIT AND Apache-2.0
-
-Files: tests/thirdparty/doctest/*
-Copyright: 2016-2023 Viktor Kirilov
-License: MIT
-
-Files: tests/thirdparty/fifo_map/*
-Copyright: 2015-2017 Niels Lohmann
-License: MIT
-
-Files: tests/thirdparty/imapdl/*
-Copyright: 2017 Georg Sauthoff <mail@gms.tf>
-License: GPL-3.0-only
-
-Files: tools/amalgamate/*
-Copyright: 2012 Erik Edlund <erik.edlund@32767.se>
-License: BSD-3-Clause
-
-Files: tools/gdb_pretty_printer/*
-Copyright: 2020 Hannes Domani <https://github.com/ssbssa>
-License: MIT
@@ -80,6 +80,7 @@ cc_library(
    name = "singleheader-json",
    hdrs = [
        "single_include/nlohmann/json.hpp",
+        "single_include/nlohmann/json_fwd.hpp",
    ],
    includes = ["single_include"],
    visibility = ["//visibility:public"],
@@ -10,5 +10,5 @@ title: "JSON for Modern C++"
 version: 3.12.0
 date-released: 2025-04-07
 license: MIT
-repository-code: "https://github.com/nlohmann"
+repository-code: "https://github.com/nlohmann/json"
 url: https://json.nlohmann.me
@@ -42,8 +42,11 @@ endif()
 ## OPTIONS
 ##

+# Build the tests by default only for the main project and only if the tests
+# directory exists (the release archive json.tar.xz does not contain it).
 # VERSION_GREATER_EQUAL is not available in older CMake (< 3.7)
-if(${MAIN_PROJECT} AND (${CMAKE_VERSION} VERSION_EQUAL 3.13 OR ${CMAKE_VERSION} VERSION_GREATER 3.13))
+if(${MAIN_PROJECT} AND (${CMAKE_VERSION} VERSION_EQUAL 3.13 OR ${CMAKE_VERSION} VERSION_GREATER 3.13)
+   AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/tests/CMakeLists.txt")
    set(JSON_BuildTests_INIT ON)
 else()
    set(JSON_BuildTests_INIT OFF)
@@ -62,6 +65,7 @@ option(JSON_MultipleHeaders                "Use non-amalgamated version of the l
 option(JSON_SystemInclude                  "Include as system headers (skip for clang-tidy)." OFF)
 option(JSON_StrictNulHandling              "Build with strict NUL-byte handling enabled." OFF)
 option(JSON_StrictBinaryUTF8               "Build with UTF-8 checks in the CBOR, UBJSON, BJData, and BSON writers enabled." OFF)
+option(JSON_DeleteDeprecatedFunctions      "Delete the deprecated functions instead of only deprecating them." OFF)

 if (JSON_CI)
    include(ci)
@@ -123,6 +127,10 @@ if (JSON_StrictBinaryUTF8)
    message(STATUS "Strict UTF-8 checks in binary writers enabled (JSON_STRICT_BINARY_UTF8=1)")
 endif()

+if (JSON_DeleteDeprecatedFunctions)
+    message(STATUS "Deprecated functions are deleted (JSON_DELETE_DEPRECATED_FUNCTIONS=1)")
+endif()
+
 if (JSON_Diagnostic_Positions)
    message(STATUS "Diagnostic positions enabled (JSON_DIAGNOSTIC_POSITIONS=1)")
 endif()
@@ -159,6 +167,7 @@ target_compile_definitions(
    $<$<BOOL:${JSON_LegacyDiscardedValueComparison}>:JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1>
    $<$<BOOL:${JSON_StrictNulHandling}>:JSON_STRICT_NUL_HANDLING=1>
    $<$<BOOL:${JSON_StrictBinaryUTF8}>:JSON_STRICT_BINARY_UTF8=1>
+    $<$<BOOL:${JSON_DeleteDeprecatedFunctions}>:JSON_DELETE_DEPRECATED_FUNCTIONS=1>
 )

 target_include_directories(
@@ -196,19 +196,19 @@ Further documentation:

 ## REUSE

-### `.reuse/dep5`
+### `REUSE.toml`

 The file defines the licenses of certain third-party components in the repository. The root `Makefile` contains a target `reuse` that checks for compliance.

 Further documentation:

- [DEP5](https://reuse.software/spec-3.2/#dep5-deprecated)
+- [REUSE.toml](https://reuse.software/spec-3.3/#reusetoml)
 - [reuse command-line tool](https://pypi.org/project/reuse/)
 - [documentation of linting](https://reuse.readthedocs.io/en/stable/man/reuse-lint.html)
 - [REUSE](http://reuse.software)

 > [!IMPORTANT]
-> The filename `.reuse/dep5` is predetermined by REUSE. Alternatively, a `REUSE.toml` file can be used.
+> The filename `REUSE.toml` is predetermined by REUSE. Alternatively, a `.reuse/dep5` file (deprecated) can be used.

 ### `.reuse/templates`

@@ -7,6 +7,9 @@
 # find GNU sed to use `-i` parameter
 SED:=$(shell command -v gsed || which sed)

+# find GNU tar to use `--sort` and `--pax-option` parameters
+TAR:=$(shell command -v gtar || which tar)
+

 ##########################################################################
 # source files
@@ -174,8 +177,8 @@ ChangeLog.md:
 # archive is created according to the advices of <https://reproducible-builds.org/docs/archives/>.
 json.tar.xz:
 	mkdir json
-	rsync -R $(shell find LICENSE.MIT nlohmann_json.natvis CMakeLists.txt cmake/*.in include single_include -type f) json
-	gtar --sort=name --mtime="@$(shell git log -1 --pretty=%ct)" --owner=0 --group=0 --numeric-owner --pax-option=exthdr.name=%d/PaxHeaders/%f,delete=atime,delete=ctime --create --file - json | xz --compress -9e --threads=2 - > json.tar.xz
+	rsync -R $(shell find LICENSE.MIT nlohmann_json.natvis CMakeLists.txt cmake/*.in include single_include src/modules -type f) json
+	$(TAR) --sort=name --mtime="@$(shell git log -1 --pretty=%ct)" --owner=0 --group=0 --numeric-owner --pax-option=exthdr.name=%d/PaxHeaders/%f,delete=atime,delete=ctime --create --file - json | xz --compress -9e --threads=2 - > json.tar.xz
 	rm -fr json

 # We use `-X` to make the resulting ZIP file reproducible, see
@@ -6,7 +6,7 @@ import PackageDescription
 let package = Package(
    name: "nlohmann-json",
     platforms: [
-        .iOS(.v12), .macOS(.v10_13), .tvOS(.v12), .watchOS(.v4), .visionOS(.v1)
+        .iOS(.v12), .macOS(.v10_13), .tvOS(.v12), .watchOS(.v9), .visionOS(.v1)
    ],
    products: [
        .library(name: "json", targets: ["json"])
@@ -7,7 +7,7 @@
 [![Coverage Status](https://coveralls.io/repos/github/nlohmann/json/badge.svg?branch=develop)](https://coveralls.io/github/nlohmann/json?branch=develop)
 [![Coverity Scan Build Status](https://scan.coverity.com/projects/5550/badge.svg)](https://scan.coverity.com/projects/nlohmann-json)
 [![Codacy Badge](https://app.codacy.com/project/badge/Grade/e0d1a9d5d6fd46fcb655c4cb930bb3e8)](https://app.codacy.com/gh/nlohmann/json/dashboard?utm_source=gh&utm_medium=referral&utm_content=&utm_campaign=Badge_grade)
-[![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/json.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:json)
+[![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/json.svg)](https://issues.oss-fuzz.com/issues?q=project:json)
 [![Try online](https://img.shields.io/badge/try-online-blue.svg)](https://wandbox.org/permlink/1mp10JbaANo6FUc7)
 [![Documentation](https://img.shields.io/badge/docs-mkdocs-blue.svg)](https://json.nlohmann.me)
 [![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/nlohmann/json/develop/LICENSE.MIT)
@@ -104,7 +104,7 @@ 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. 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.
+: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.

 :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.

@@ -1202,15 +1202,18 @@ language bindings, format converters, and the like. See the curated [Ecosystem](

 Though it's 2026 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:

- GCC 4.8 - 14.2 (and possibly later)
- Clang 3.4 - 21.0 (and possibly later)
- Apple Clang 9.1 - 16.0 (and possibly later)
- Intel C++ Compiler 17.0.2 (and possibly later)
- Nvidia CUDA Compiler 11.0.221 (and possibly later)
- Microsoft Visual C++ 2015 / Build Tools 14.0.25123.0 (and possibly later)
- Microsoft Visual C++ 2017 / Build Tools 15.5.180.51428 (and possibly later)
- Microsoft Visual C++ 2019 / Build Tools 16.3.1+1def00d3d (and possibly later)
- Microsoft Visual C++ 2022 / Build Tools 19.30.30709.0 (and possibly later)
+- GCC 4.8 - 16.2 (and possibly later)
+- Clang 3.4 - 22.1 (and possibly later)
+- Apple Clang 15.0 - 21.0 (and possibly later)
+- Intel C++ Compiler Classic (icpc) 2021.10
+- Intel oneAPI DPC++/C++ Compiler (icpx) 2025.3 (and possibly later)
+- NVIDIA CUDA Compiler (nvcc) 11.8 - 12.6 (and possibly later)
+- NVIDIA HPC SDK C++ Compiler (nvc++) 25.5 (and possibly later)
+- Microsoft Visual C++ 2015 / MSVC 19.0 (and possibly later)
+- Microsoft Visual C++ 2017 / MSVC 19.16 (and possibly later)
+- Microsoft Visual C++ 2019 / MSVC 19.29 (and possibly later)
+- Microsoft Visual C++ 2022 / MSVC 19.44 (and possibly later)
+- Microsoft Visual C++ 2026 / MSVC 19.51 (and possibly later)

 I would be happy to learn about other compilers/versions.

@@ -1401,7 +1404,7 @@ The library is compliant to version 3.3 of the [**REUSE specification**](https:/

 - Every source file contains an SPDX copyright header.
 - The full text of all licenses used in the repository can be found in the `LICENSES` folder.
- File `.reuse/dep5` contains an overview of all files' copyrights and licenses.
+- File `REUSE.toml` contains an overview of all files' copyrights and licenses.
 - Run `pipx run reuse lint` to verify the project's REUSE compliance and `pipx run reuse spdx` to generate a SPDX SBOM.

 ## Contact
@@ -0,0 +1,52 @@
+version = 1
+SPDX-PackageName = "json"
+SPDX-PackageSupplier = "Niels Lohmann <mail@nlohmann.me>"
+SPDX-PackageDownloadLocation = "https://github.com/nlohmann/json"
+
+[[annotations]]
+path = "**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2013-2026 Niels Lohmann <https://nlohmann.me>"
+SPDX-License-Identifier = "MIT"
+
+[[annotations]]
+path = "include/nlohmann/thirdparty/hedley.hpp"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2016-2021 Evan Nemerson <evan@nemerson.com>"
+SPDX-License-Identifier = "CC0"
+
+[[annotations]]
+path = "include/nlohmann/detail/meta/cpp_future.hpp"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2013-2026 Niels Lohmann <https://nlohmann.me> and 2018 The Abseil Authors"
+SPDX-License-Identifier = "MIT AND Apache-2.0"
+
+[[annotations]]
+path = "tests/thirdparty/doctest/**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2016-2023 Viktor Kirilov"
+SPDX-License-Identifier = "MIT"
+
+[[annotations]]
+path = "tests/thirdparty/fifo_map/**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2015-2017 Niels Lohmann"
+SPDX-License-Identifier = "MIT"
+
+[[annotations]]
+path = "tests/thirdparty/imapdl/**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2017 Georg Sauthoff <mail@gms.tf>"
+SPDX-License-Identifier = "GPL-3.0-only"
+
+[[annotations]]
+path = "tools/amalgamate/**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2012 Erik Edlund <erik.edlund@32767.se>"
+SPDX-License-Identifier = "BSD-3-Clause"
+
+[[annotations]]
+path = "tools/gdb_pretty_printer/**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2020 Hannes Domani <https://github.com/ssbssa>"
+SPDX-License-Identifier = "MIT"
@@ -249,6 +249,20 @@ add_custom_target(ci_test_strict_nul_handling
    COMMENT "Compile and test with strict NUL-byte handling enabled"
 )

+###############################################################################
+# Delete the deprecated functions.
+###############################################################################
+
+add_custom_target(ci_test_delete_deprecated_functions
+    COMMAND ${CMAKE_COMMAND}
+    -DCMAKE_BUILD_TYPE=Debug -GNinja
+    -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_DeleteDeprecatedFunctions=ON
+    -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_delete_deprecated_functions
+    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_delete_deprecated_functions
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_delete_deprecated_functions && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
+    COMMENT "Compile and test with the deprecated functions deleted"
+)
+
 ###############################################################################
 # Disable global UDLs.
 ###############################################################################
@@ -362,7 +376,7 @@ add_custom_target(ci_test_coverage
 # Sanitizers.
 ###############################################################################

-set(CLANG_CXX_FLAGS_SANITIZER "-g -O1 -fsanitize=address -fsanitize=undefined -fsanitize=integer -fsanitize=nullability -fno-omit-frame-pointer -fno-sanitize-recover=all -fno-sanitize=unsigned-integer-overflow -fno-sanitize=unsigned-shift-base")
+set(CLANG_CXX_FLAGS_SANITIZER "-g -O1 -fsanitize=address -fsanitize=undefined -fsanitize=integer -fsanitize=nullability -fno-omit-frame-pointer -fno-sanitize-recover=all -fno-sanitize=unsigned-integer-overflow -fno-sanitize=unsigned-shift-base -fsanitize-ignorelist=${PROJECT_SOURCE_DIR}/cmake/clang_sanitizer_ignorelist.txt")

 add_custom_target(ci_test_clang_sanitizer
    COMMAND CXX=${CLANG_TOOL} CXXFLAGS=${CLANG_CXX_FLAGS_SANITIZER} ${CMAKE_COMMAND}
@@ -442,13 +456,14 @@ add_custom_target(ci_test_single_header
 # Valgrind.
 ###############################################################################

+# The Unicode test (~17M assertions) is too slow under Valgrind.
 add_custom_target(ci_test_valgrind
    COMMAND CXX=${GCC_TOOL} ${CMAKE_COMMAND}
        -DCMAKE_BUILD_TYPE=Debug -GNinja
        -DJSON_BuildTests=ON -DJSON_Valgrind=ON
        -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_valgrind
    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_valgrind
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_valgrind && ${CMAKE_CTEST_COMMAND} -L valgrind --parallel ${N} --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_valgrind && ${CMAKE_CTEST_COMMAND} -L valgrind --exclude-regex "test-unicode" --parallel ${N} --output-on-failure
    COMMENT "Compile and test with Valgrind"
 )

@@ -705,7 +720,7 @@ ci_get_cmake(4.0.0  CMAKE_4_0_0_BINARY)
 # the tests require CMake 3.13 or later, so they are excluded for CMake 3.5.0
 set(JSON_CMAKE_FLAGS_3_5_0 JSON_Diagnostics JSON_Diagnostic_Positions JSON_GlobalUDLs JSON_ImplicitConversions JSON_DisableEnumSerialization
    JSON_LegacyDiscardedValueComparison JSON_Install JSON_MultipleHeaders JSON_SystemInclude JSON_Valgrind
-    JSON_StrictNulHandling JSON_StrictBinaryUTF8)
+    JSON_StrictNulHandling JSON_StrictBinaryUTF8 JSON_DeleteDeprecatedFunctions)
 set(JSON_CMAKE_FLAGS_3_31_6 JSON_BuildTests ${JSON_CMAKE_FLAGS_3_5_0})
 set(JSON_CMAKE_FLAGS_4_0_0 JSON_BuildTests ${JSON_CMAKE_FLAGS_3_5_0})

@@ -773,7 +788,7 @@ foreach(COMPILER g++-4.8 g++-4.9 g++-5 g++-6 g++-7 g++-8 g++-9 g++-10 g++-11 cla
                -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_compiler_${COMPILER}
                ${ADDITIONAL_FLAGS}
            COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_compiler_${COMPILER}
-            COMMAND cd ${PROJECT_BINARY_DIR}/build_compiler_${COMPILER} && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode" --output-on-failure
+            COMMAND cd ${PROJECT_BINARY_DIR}/build_compiler_${COMPILER} && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
            COMMENT "Compile and test with ${COMPILER}"
        )
    endif()
@@ -787,7 +802,7 @@ add_custom_target(ci_test_compiler_default
        -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_compiler_default
        ${ADDITIONAL_FLAGS}
    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_compiler_default --parallel ${N}
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_compiler_default && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode" -LE git_required --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_compiler_default && ${CMAKE_CTEST_COMMAND} --parallel ${N} -LE git_required --output-on-failure
    COMMENT "Compile and test with default C++ compiler"
 )

@@ -825,7 +840,7 @@ add_custom_target(ci_icpc
        -DJSON_BuildTests=ON -DJSON_FastTests=ON
        -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_icpc
    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_icpc
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_icpc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode" --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_icpc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
    COMMENT "Compile and test with ICPC"
 )

@@ -836,7 +851,7 @@ add_custom_target(ci_icpx
        -DJSON_BuildTests=ON -DJSON_FastTests=ON
        -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_icpx
    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_icpx
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_icpx && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode" --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_icpx && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
    COMMENT "Compile and test with ICPX (Intel oneAPI DPC++/C++)"
 )

@@ -872,7 +887,7 @@ add_custom_target(ci_nvhpc
    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_nvhpc
    # the pipes are escaped so the surrounding shell passes them to ctest verbatim
    # instead of treating them as shell pipe operators
-    COMMAND cd ${PROJECT_BINARY_DIR}/build_nvhpc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-unicode\\|test-comparison_cpp20\\|test-comparison_legacy_cpp20\\|test-constructor1_cpp11\\|test-deserialization_cpp20" --output-on-failure
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_nvhpc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --exclude-regex "test-comparison_cpp20\\|test-comparison_legacy_cpp20\\|test-constructor1_cpp11\\|test-deserialization_cpp20" --output-on-failure
    COMMENT "Compile and test with NVIDIA HPC SDK (nvc++)"
 )

@@ -0,0 +1,8 @@
+# Sanitizer ignore list for ci_test_clang_sanitizer (-fsanitize-ignorelist).
+#
+# libstdc++ 14's <format> declares `_Scanner(basic_string_view<_CharT>, size_t __nargs = -1)`, so every std::format
+# call converts -1 to size_t, which -fsanitize=integer reports as implicit-integer-sign-change. This is
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119429, not a bug in this library. Only that check and only <format> are
+# excluded, so implicit sign changes in the library and the tests are still reported.
+[implicit-integer-sign-change]
+src:*/include/c++/*/format
@@ -48,6 +48,7 @@ cc_library(
    name = "singleheader-json",
    hdrs = [
        "single_include/nlohmann/json.hpp",
+        "single_include/nlohmann/json_fwd.hpp",
    ],
    includes = ["single_include"],
    visibility = ["//visibility:public"],
@@ -64,7 +64,7 @@ if(MODE STREQUAL "undef")
    # recipe is self-contained and its output is byte-stable across reruns.
    # The embedded SPDX tags below are part of the *generated* file's
    # content, not a REUSE header for this .cmake script itself (which is
-    # already covered by the blanket "Files: *" rule in .reuse/dep5) -- keep
+    # already covered by the blanket path = "**" rule in REUSE.toml) -- keep
    # them wrapped in REUSE-IgnoreStart/End so `reuse lint` does not try to
    # parse "MIT\n")" as this file's own SPDX-License-Identifier value.
    # REUSE-IgnoreStart
@@ -9,13 +9,11 @@ INSERT INTO searchIndex(name, type, path) VALUES ('adl_serializer::to_json', 'Fu
 INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype', 'Class', 'api/byte_container_with_subtype/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::byte_container_with_subtype', 'Constructor', 'api/byte_container_with_subtype/byte_container_with_subtype/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::clear_subtype', 'Method', 'api/byte_container_with_subtype/clear_subtype/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::container_type', 'Type', 'api/byte_container_with_subtype/container_type/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::has_subtype', 'Method', 'api/byte_container_with_subtype/has_subtype/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::operator!=', 'Operator', 'api/byte_container_with_subtype/operator_ne/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::operator==', 'Operator', 'api/byte_container_with_subtype/operator_eq/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::set_subtype', 'Method', 'api/byte_container_with_subtype/set_subtype/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::subtype', 'Method', 'api/byte_container_with_subtype/subtype/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('byte_container_with_subtype::subtype_type', 'Type', 'api/byte_container_with_subtype/subtype_type/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json', 'Class', 'api/basic_json/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('format_as', 'Function', 'api/basic_json/format_as/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::accept', 'Function', 'api/basic_json/accept/index.html');
@@ -28,7 +26,6 @@ INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::basic_json', 'Con
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::begin', 'Method', 'api/basic_json/begin/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::binary', 'Function', 'api/basic_json/binary/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::binary_t', 'Type', 'api/basic_json/binary_t/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::bjdata_version_t', 'Enum', 'api/basic_json/bjdata_version_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::boolean_t', 'Type', 'api/basic_json/boolean_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::cbegin', 'Method', 'api/basic_json/cbegin/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::cbor_tag_handler_t', 'Enum', 'api/basic_json/cbor_tag_handler_t/index.html');
@@ -64,7 +61,6 @@ INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::get_binary', 'Met
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::get_ptr', 'Method', 'api/basic_json/get_ptr/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::get_ref', 'Method', 'api/basic_json/get_ref/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::get_to', 'Method', 'api/basic_json/get_to/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::initializer_list_t', 'Type', 'api/basic_json/initializer_list_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::input_format_t', 'Enum', 'api/basic_json/input_format_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::insert', 'Method', 'api/basic_json/insert/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::invalid_iterator', 'Class', 'api/basic_json/invalid_iterator/index.html');
@@ -83,7 +79,6 @@ INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::is_string', 'Meth
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::is_structured', 'Method', 'api/basic_json/is_structured/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::items', 'Method', 'api/basic_json/items/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::json_base_class_t', 'Type', 'api/basic_json/json_base_class_t/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::json_sax_t', 'Type', 'api/basic_json/json_sax_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::json_serializer', 'Class', 'api/basic_json/json_serializer/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::max_size', 'Method', 'api/basic_json/max_size/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::merge_patch', 'Method', 'api/basic_json/merge_patch/index.html');
@@ -136,6 +131,7 @@ INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::to_string', 'Meth
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::to_ubjson', 'Function', 'api/basic_json/to_ubjson/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::value', 'Method', 'api/basic_json/value/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::value_t', 'Enum', 'api/basic_json/value_t/index.html');
+INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::with_t', 'Type', 'api/basic_json/with_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('basic_json::~basic_json', 'Method', 'api/basic_json/~basic_json/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json', 'Class', 'api/json/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_pointer', 'Class', 'api/json_pointer/index.html');
@@ -158,44 +154,24 @@ INSERT INTO searchIndex(name, type, path) VALUES ('json_pointer::string_t', 'Typ
 INSERT INTO searchIndex(name, type, path) VALUES ('json_pointer::to_string', 'Method', 'api/json_pointer/to_string/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax', 'Class', 'api/json_sax/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::binary', 'Method', 'api/json_sax/binary/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::binary_t', 'Type', 'api/json_sax/binary_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::boolean', 'Method', 'api/json_sax/boolean/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::end_array', 'Method', 'api/json_sax/end_array/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::end_object', 'Method', 'api/json_sax/end_object/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::json_sax', 'Constructor', 'api/json_sax/json_sax/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::key', 'Method', 'api/json_sax/key/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::null', 'Method', 'api/json_sax/null/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::number_float', 'Method', 'api/json_sax/number_float/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::number_float_t', 'Type', 'api/json_sax/number_float_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::number_integer', 'Method', 'api/json_sax/number_integer/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::number_integer_t', 'Type', 'api/json_sax/number_integer_t/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::number_unsigned', 'Method', 'api/json_sax/number_unsigned/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::number_unsigned_t', 'Type', 'api/json_sax/number_unsigned_t/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::operator=', 'Operator', 'api/json_sax/operator=/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::parse_error', 'Method', 'api/json_sax/parse_error/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::start_array', 'Method', 'api/json_sax/start_array/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::start_object', 'Method', 'api/json_sax/start_object/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::string', 'Method', 'api/json_sax/string/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::string_t', 'Type', 'api/json_sax/string_t/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('json_sax::~json_sax', 'Method', 'api/json_sax/~json_sax/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator""_json', 'Literal', 'api/operator_literal_json/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator""_json_pointer', 'Literal', 'api/operator_literal_json_pointer/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator<<', 'Operator', 'api/operator_ltlt/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator>>', 'Operator', 'api/operator_gtgt/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('ordered_json', 'Class', 'api/ordered_json/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map', 'Class', 'api/ordered_map/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::Container', 'Type', 'api/ordered_map/Container/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::at', 'Method', 'api/ordered_map/at/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::count', 'Method', 'api/ordered_map/count/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::emplace', 'Method', 'api/ordered_map/emplace/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::erase', 'Method', 'api/ordered_map/erase/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::find', 'Method', 'api/ordered_map/find/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::insert', 'Method', 'api/ordered_map/insert/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::key_compare', 'Type', 'api/ordered_map/key_compare/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::operator=', 'Operator', 'api/ordered_map/operator=/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::operator[]', 'Operator', 'api/ordered_map/operator[]/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::ordered_map', 'Constructor', 'api/ordered_map/ordered_map/index.html');
-INSERT INTO searchIndex(name, type, path) VALUES ('ordered_map::~ordered_map', 'Method', 'api/ordered_map/~ordered_map/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('std::formatter<basic_json>', 'Class', 'api/basic_json/std_formatter/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('std::hash<basic_json>', 'Class', 'api/basic_json/std_hash/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('std::swap<basic_json>', 'Function', 'api/basic_json/std_swap/index.html');
@@ -244,6 +220,7 @@ INSERT INTO searchIndex(name, type, path) VALUES ('Supported Macros', 'Guide', '
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_ASSERT', 'Macro', 'api/macros/json_assert/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_BRACE_INIT_COPY_SEMANTICS', 'Macro', 'api/macros/json_brace_init_copy_semantics/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_CATCH_USER', 'Macro', 'api/macros/json_throw_user/index.html');
+INSERT INTO searchIndex(name, type, path) VALUES ('JSON_DELETE_DEPRECATED_FUNCTIONS', 'Macro', 'api/macros/json_delete_deprecated_functions/index.html');
 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');
@@ -274,6 +251,7 @@ INSERT INTO searchIndex(name, type, path) VALUES ('JSON_TRY_USER', 'Macro', 'api
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_GLOBAL_UDLS', 'Macro', 'api/macros/json_use_global_udls/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_IMPLICIT_CONVERSIONS', 'Macro', 'api/macros/json_use_implicit_conversions/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON', 'Macro', 'api/macros/json_use_legacy_discarded_value_comparison/index.html');
+INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS', 'Macro', 'api/macros/json_use_objects_for_enum_keyed_maps/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('JSON_USE_SIMDUTF', 'Macro', 'api/macros/json_use_simdutf/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('Macros', 'Macro', 'api/macros/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE', 'Macro', 'api/macros/nlohmann_define_derived_type/index.html');
@@ -475,10 +475,8 @@ 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. 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. Explicit
-   for different string types if `JSON_USE_IMPLICIT_CONVERSIONS` is `0` since version 3.13.0.
+4. Since version 3.2.0. Explicit for different string types if `JSON_USE_IMPLICIT_CONVERSIONS` is `0` since
+   version 3.13.0.
 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
@@ -1,38 +0,0 @@
-# <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.
@@ -9,10 +9,10 @@ enum class cbor_tag_handler_t
 };
 ```

-This enumeration is used in the [`from_cbor`](from_cbor.md) function to choose how to treat tags:
+This enumeration is used in [`from_cbor`](from_cbor.md) and [`sax_parse`](sax_parse.md) to choose how to treat tags:

 error
-:   throw a `parse_error` exception in case of a tag
+:   report a parse error in case of a tag (the `from_cbor` overloads throw a `parse_error` exception by default)

 ignore
 :   ignore tags
@@ -8,7 +8,7 @@ static basic_json diff(const basic_json& source,
 Creates a [JSON Patch](http://jsonpatch.com) so that value `source` can be changed into the value `target` by calling
 [`patch`](patch.md) function.

-For two JSON values `source` and `target`, the following code yields always `#!cpp true`:
+For two JSON values `source` and `target`, the following code always yields `#!cpp true`:
 ```cpp
 source.patch(diff(source, target)) == target;
 ```
@@ -27,7 +27,7 @@ a JSON patch to convert the `source` to `target`

 ## Exception safety

-Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
+Strong guarantee: `source` and `target` are never modified.

 ## Complexity

@@ -120,3 +120,12 @@ Linear in the size of the input.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 - Added `error_handler` parameter in version 3.13.0.
+
+!!! warning "Deprecation"
+
+    - Overload (2) replaces calls to `from_bjdata` with a pointer and a length as first two parameters, which has been
+      deprecated in version 3.13.0. This overload will be removed in version 4.0.0. Please replace all calls like
+      `#!cpp from_bjdata(ptr, len, ...);` with `#!cpp from_bjdata(ptr, ptr+len, ...);`.
+
+    You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
+    function.
@@ -106,3 +106,12 @@ Linear in the size of the input.
 ## Version history

 - Added in version 3.13.0.
+
+!!! warning "Deprecation"
+
+    - Overload (2) replaces calls to `from_bon8` with a pointer and a length as first two parameters, which has been
+      deprecated in version 3.13.0. This overload will be removed in version 4.0.0. Please replace all calls like
+      `#!cpp from_bon8(ptr, len, ...);` with `#!cpp from_bon8(ptr, ptr+len, ...);`.
+
+    You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
+    function.
@@ -109,6 +109,9 @@ The class satisfies the following concept requirements:
 - **initializer_list_t** - type for initializer lists of `basic_json` values
 - [**input_format_t**](input_format_t.md) - type to choose the format to parse
 - [**json_sax_t**](../json_sax/index.md) - type for SAX events
+- [**with_object_t, with_array_t, with_string_t, with_boolean_t, with_integers_t, with_float_t, with_allocator_t,
+  with_json_serializer_t, with_binary_t, with_base_class_t**](with_t.md) - types to create a `basic_json` type with
+  one (or two) replaced template parameters

 ### Exceptions

@@ -1,32 +0,0 @@
-# <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.
@@ -1,31 +0,0 @@
-# <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.
@@ -55,6 +55,10 @@ This implementation does exactly follow this approach, as it uses double precisi
 smaller than `-1.79769313486232e+308` and values greater than `1.79769313486232e+308` will be stored as NaN internally
 and be serialized to `null`.

+During deserialization (from JSON text or any of the binary formats), a finite number that does not fit into
+`number_float_t` is rejected with [`out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406), for
+example a double-precision number in a binary format when `number_float_t` is `#!cpp float`.
+
 ### Storage

 Floating-point number values are stored directly inside a `basic_json` type.
@@ -47,8 +47,9 @@ With the default values for `NumberIntegerType` (`std::int64_t`), the default va

 When the default type is used, the maximal integer number that can be stored is `9223372036854775807` (INT64_MAX) and
 the minimal integer number that can be stored is `-9223372036854775808` (INT64_MIN). Integer numbers that are out of
-range will yield over/underflow when used in a constructor. During deserialization, too large or small integer numbers
-will automatically be stored as [`number_unsigned_t`](number_unsigned_t.md) or [`number_float_t`](number_float_t.md).
+range will yield over/underflow when used in a constructor. During deserialization (from JSON text or any of the binary
+formats), too large or small integer numbers will automatically be stored as [`number_unsigned_t`](number_unsigned_t.md)
+or [`number_float_t`](number_float_t.md).

 [RFC 8259](https://tools.ietf.org/html/rfc8259) further states:
 > Note that when such software is used, numbers that are integers and are in the range [-2<sup>53</sup>+1, 2<sup>53</sup>-1] are
@@ -48,8 +48,9 @@ With the default values for `NumberUnsignedType` (`std::uint64_t`), the default

 When the default type is used, the maximal integer number that can be stored is `18446744073709551615` (UINT64_MAX) and
 the minimal integer number that can be stored is `0`. Integer numbers that are out of range will yield over/underflow
-when used in a constructor. During deserialization, too large or small integer numbers will automatically be stored
-as [`number_integer_t`](number_integer_t.md) or [`number_float_t`](number_float_t.md).
+when used in a constructor. During deserialization (from JSON text or any of the binary formats), too large or small
+integer numbers will automatically be stored as [`number_integer_t`](number_integer_t.md) or
+[`number_float_t`](number_float_t.md).

 [RFC 8259](https://tools.ietf.org/html/rfc8259) further states:
 > Note that when such software is used, numbers that are integers and are in the range [-2<sup>53</sup>+1, 2<sup>53</sup>-1] are
@@ -51,5 +51,3 @@ 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.
@@ -92,8 +92,3 @@ 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)).
@@ -8,7 +8,8 @@ static bool sax_parse(InputType&& i,
                      input_format_t format = input_format_t::json,
                      const bool strict = true,
                      const bool ignore_comments = false,
-                      const bool ignore_trailing_commas = false);
+                      const bool ignore_trailing_commas = false,
+                      const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);

 // (2)
 template<class IteratorType, class SAX, class SentinelType = IteratorType>
@@ -17,13 +18,14 @@ static bool sax_parse(IteratorType first, SentinelType last,
                      input_format_t format = input_format_t::json,
                      const bool strict = true,
                      const bool ignore_comments = false,
-                      const bool ignore_trailing_commas = false);
+                      const bool ignore_trailing_commas = false,
+                      const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);
 ```

 Read from input and generate SAX events

 1. Read from a compatible input.
-2. Read from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)
+2. Read from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support).
    
    The value_type of the iterator must be an integral type with a size of 1, 2, or 4 bytes, which will be interpreted
    respectively as UTF-8, UTF-16, and UTF-32. If `SentinelType` differs from `IteratorType`, it must be comparable to
@@ -82,6 +84,10 @@ The SAX event lister must follow the interface of [`json_sax`](../json_sax/index
 :   whether trailing commas in arrays or objects should be ignored and treated like whitespace (`#!cpp true`) or yield a parse error
    (`#!cpp false`); (optional, `#!cpp false` by default)

+`tag_handler` (in)
+:   how to handle CBOR tags; see [`cbor_tag_handler_t`](cbor_tag_handler_t.md). Ignored for formats other than CBOR
+    (optional, `cbor_tag_handler_t::error` by default).
+
 `first` (in)
 :   iterator to the start of a character range

@@ -137,6 +143,7 @@ A UTF-8 byte order mark is silently ignored.
 - Added in version 3.2.0.
 - Ignoring comments via `ignore_comments` added in version 3.9.0.
 - Added `ignore_trailing_commas` in version 3.13.0.
+- Added `tag_handler` in version 3.13.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 - `JSON_PRECISE_STREAM_POSITION` added in version 3.13.0 to optionally leave a `#!cpp std::istream` positioned right
@@ -68,6 +68,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
  not valid UTF-8 and `error_handler` is `strict` (the default only if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
+  discarded; example: `"cannot serialize discarded value to BJData"`

 ## Complexity

@@ -119,4 +121,6 @@ Linear in the size of the JSON value `j`.
 - BJData version parameter (for draft3 binary encoding) added in version 3.12.0.
 - Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
  that is not valid UTF-8 unchanged, as before; `strict` (the default if
-  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
+  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
+- Throws `type_error.321` for a discarded value since version 3.13.0; previously, a discarded value nested in an
+  array or object was silently skipped, producing invalid BJData.
@@ -58,6 +58,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key is
  not valid UTF-8 and `error_handler` is `strict` (the default only if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if a value nested in `j` is discarded
+  (the top-level value itself is covered by `type_error.317` above, since it must be an object); example:
+  `"cannot serialize discarded value to BSON"`

 ## Complexity

@@ -110,6 +113,8 @@ pass before anything is written.
 - Throws `out_of_range.412` and `out_of_range.415` since version 3.13.0.
 - 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.
+- Throws `type_error.321` for a discarded value nested in `j` since version 3.13.0; previously, it was silently
+  skipped, producing a document whose declared size did not match what was actually written.
 - Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
  that is not valid UTF-8 unchanged, as before; `strict` (the default if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316` before anything
@@ -49,6 +49,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
  not valid UTF-8 and `error_handler` is `strict` (the default only if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
+  discarded; example: `"cannot serialize discarded value to CBOR"`

 ## Complexity

@@ -86,3 +88,5 @@ Linear in the size of the JSON value `j`.
 - Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
  that is not valid UTF-8 unchanged, as before; `strict` (the default if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
+- Throws `type_error.321` for a discarded value since version 3.13.0; previously, a discarded value nested in an
+  array or object was silently skipped, producing invalid CBOR.
@@ -54,6 +54,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
  `"subtype 70000 is too large for the MessagePack ext type (max 255)"`
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
  not valid UTF-8 and `error_handler` is `strict`
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
+  discarded; example: `"cannot serialize discarded value to MessagePack"`

 ## Complexity

@@ -108,3 +110,5 @@ Linear in the size of the JSON value `j`.
 - Fixed in version 3.13.0 to serialize `number_integer_t`/`number_unsigned_t` pairs of different width correctly;
  before, integers could be serialized with the wrong value if `number_integer_t` was narrower than
  `number_unsigned_t`.
+- Throws `type_error.321` for a discarded value since version 3.13.0; previously, a discarded value nested in an
+  array or object was silently skipped, producing invalid MessagePack.
@@ -61,6 +61,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
  not valid UTF-8 and `error_handler` is `strict` (the default only if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
+- Throws [type_error.321](../../home/exceptions.md#jsonexceptiontype_error321) if `j` or a value nested in it is
+  discarded; example: `"cannot serialize discarded value to UBJSON"`

 ## Complexity

@@ -112,3 +114,5 @@ Linear in the size of the JSON value `j`.
 - Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
  that is not valid UTF-8 unchanged, as before; `strict` (the default if
  [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
+- Throws `type_error.321` for a discarded value since version 3.13.0; previously, a discarded value nested in an
+  array or object was silently skipped, producing invalid UBJSON.
@@ -0,0 +1,136 @@
+# <small>nlohmann::basic_json::</small>with_t
+
+Member alias templates `with_object_t`, `with_array_t`, `with_string_t`, `with_boolean_t`, `with_integers_t`,
+`with_float_t`, `with_allocator_t`, `with_json_serializer_t`, `with_binary_t`, and `with_base_class_t`.
+
+```cpp
+template<template<typename, typename, typename...> class ObjectType2>
+using with_object_t = basic_json<ObjectType2, ArrayType, StringType, BooleanType,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType,
+      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+template<template<typename, typename...> class ArrayType2>
+using with_array_t = basic_json<ObjectType, ArrayType2, StringType, BooleanType,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType,
+      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+template<class StringType2>
+using with_string_t = basic_json<ObjectType, ArrayType, StringType2, BooleanType,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType,
+      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+template<class BooleanType2>
+using with_boolean_t = basic_json<ObjectType, ArrayType, StringType, BooleanType2,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType,
+      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+template<class NumberIntegerType2, class NumberUnsignedType2>
+using with_integers_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
+      NumberIntegerType2, NumberUnsignedType2, NumberFloatType,
+      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+template<class NumberFloatType2>
+using with_float_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType2,
+      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+template<template<typename> class AllocatorType2>
+using with_allocator_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType,
+      AllocatorType2, JSONSerializer, BinaryType, CustomBaseClass>;
+
+template<template<typename, typename = void> class JSONSerializer2>
+using with_json_serializer_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType,
+      AllocatorType, JSONSerializer2, BinaryType, CustomBaseClass>;
+
+template<class BinaryType2>
+using with_binary_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType,
+      AllocatorType, JSONSerializer, BinaryType2, CustomBaseClass>;
+
+template<class CustomBaseClass2>
+using with_base_class_t = basic_json<ObjectType, ArrayType, StringType, BooleanType,
+      NumberIntegerType, NumberUnsignedType, NumberFloatType,
+      AllocatorType, JSONSerializer, BinaryType, CustomBaseClass2>;
+```
+
+These member alias templates make it easier to create a `basic_json` type that is identical to the current type except
+for one (or, in the case of `with_integers_t`, two) of its [template parameters](index.md#template-parameters).
+Spelling out all 11 template parameters of `basic_json` just to change a single one is verbose and error-prone; these
+aliases only require the replacement type(s).
+
+with_object_t&lt;ObjectType2&gt;
+:   replaces `ObjectType`
+
+with_array_t&lt;ArrayType2&gt;
+:   replaces `ArrayType`
+
+with_string_t&lt;StringType2&gt;
+:   replaces `StringType`
+
+with_boolean_t&lt;BooleanType2&gt;
+:   replaces `BooleanType`
+
+with_integers_t&lt;NumberIntegerType2, NumberUnsignedType2&gt;
+:   replaces both `NumberIntegerType` and `NumberUnsignedType`; the two are combined into a single alias because they
+    are usually changed together (for instance, when switching to fixed-width integer types)
+
+with_float_t&lt;NumberFloatType2&gt;
+:   replaces `NumberFloatType`
+
+with_allocator_t&lt;AllocatorType2&gt;
+:   replaces `AllocatorType`
+
+with_json_serializer_t&lt;JSONSerializer2&gt;
+:   replaces `JSONSerializer`
+
+with_binary_t&lt;BinaryType2&gt;
+:   replaces `BinaryType`
+
+with_base_class_t&lt;CustomBaseClass2&gt;
+:   replaces `CustomBaseClass`; see also [`json_base_class_t`](json_base_class_t.md)
+
+## Notes
+
+All other template parameters are kept unchanged, so the resulting type still uses, for instance, the same
+`ObjectType` unless `with_object_t` itself is used.
+
+The aliases are members of every `basic_json` specialization, including [`ordered_json`](../ordered_json.md), and the
+type they produce is again a `basic_json` specialization. They can therefore be chained to replace several template
+parameters at once:
+
+```cpp
+using my_json = nlohmann::json::with_integers_t<int, unsigned int>::with_float_t<float>;
+using my_ordered_json = nlohmann::ordered_json::with_string_t<std::wstring>;
+```
+
+The result is the same type as spelling out all template parameters, so the order of the chained aliases does not
+matter. For instance, `nlohmann::json::with_object_t<nlohmann::ordered_map>` is `nlohmann::ordered_json`.
+
+## Examples
+
+??? example
+
+    The following code shows how `with_object_t` can be used to create a JSON type that stores object elements in a
+    `std::map` and therefore keeps them sorted by key, unlike the default type which preserves insertion order
+    only when `nlohmann::ordered_json` is used.
+
+    ```cpp
+    --8<-- "examples/with_t.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/with_t.output"
+    ```
+
+## See also
+
+- [basic_json](index.md#template-parameters) - the template parameters that can be replaced
+- [json_base_class_t](json_base_class_t.md) - the type used for `CustomBaseClass`
+
+## Version history
+
+- Added in version 3.13.0.
@@ -1,32 +0,0 @@
-# <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.
@@ -1,28 +0,0 @@
-# <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.
@@ -1,30 +0,0 @@
-# <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.
@@ -1,33 +0,0 @@
-# <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.
@@ -1,30 +0,0 @@
-# <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.
@@ -1,30 +0,0 @@
-# <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.
@@ -1,30 +0,0 @@
-# <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.
@@ -1,29 +0,0 @@
-# <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.
@@ -1,30 +0,0 @@
-# <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.
@@ -1,22 +0,0 @@
-# <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.
@@ -58,6 +58,13 @@ header. See also the [macro overview page](../../features/macros.md).
 - [**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
+- [**JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS**](json_use_objects_for_enum_keyed_maps.md) - opt in to storing maps with enum
+  keys as objects
+
+## Deprecated functions
+
+- [**JSON_DELETE_DEPRECATED_FUNCTIONS**](json_delete_deprecated_functions.md) - opt in to deleting the deprecated
+  functions ahead of their removal in version 4.0.0

 ## Comparison behavior

@@ -50,9 +50,11 @@ The default value is `0` (disabled — existing behavior is preserved).
    ```

    Code that relies on these producing arrays must use `json::array()` instead (see below). Lists with more than one
-    element, and a single `[string, value]` pair such as `{{"key", "value"}}`, which still creates an object, are not
-    affected. The library's own conversions are not affected either: for example, `std::tuple<int>{5}` still becomes
-    `[5]`.
+    element, and a single `[string, value]` pair *written as a braced list*, such as `{{"key", "value"}}`, which still
+    creates an object, are not affected. This exception is based on how the pair is written, not on the shape of its
+    value: an existing JSON value that happens to be a two-element array with a string as its first element, such as
+    `json arr = {"key", 42};`, is still copied by `json j{arr};` rather than turned into an object. The library's own
+    conversions are not affected either: for example, `std::tuple<int>{5}` still becomes `[5]`.

 !!! note "ABI compatibility"

@@ -0,0 +1,96 @@
+# JSON_DELETE_DEPRECATED_FUNCTIONS
+
+```cpp
+#define JSON_DELETE_DEPRECATED_FUNCTIONS /* value */
+```
+
+When defined to `1`, all [deprecated functions](../../community/roadmap.md#removal-of-deprecated-functions) of the
+library are declared as deleted (`= delete`) instead of only being marked as deprecated. Code that still calls one of
+them no longer compiles. This way, you can find all calls that need to be replaced before version 4.0.0 removes these
+functions; the [migration guide](../../integration/migration_guide.md#replace-deprecated-functions) describes how.
+
+A deleted function, unlike a removed one, still takes part in overload resolution. A call that would select it
+therefore fails to compile instead of silently selecting another overload. This matters for the deprecated
+`from_*(ptr, len)` overloads of [`from_cbor`](../basic_json/from_cbor.md), [`from_msgpack`](../basic_json/from_msgpack.md),
+[`from_ubjson`](../basic_json/from_ubjson.md), [`from_bjdata`](../basic_json/from_bjdata.md),
+[`from_bon8`](../basic_json/from_bon8.md), and [`from_bson`](../basic_json/from_bson.md): without them, a call like
+`from_cbor(ptr, len)` would compile, read `ptr` as a NUL-terminated string, and convert `len` to the `strict` parameter.
+
+The macro does not affect the deprecated legacy comparison of discarded values, which is controlled by
+[`JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](json_use_legacy_discarded_value_comparison.md).
+
+## Default definition
+
+The default value is `0` (disabled, the deprecated functions can still be called, and the compiler warns about it).
+
+```cpp
+#define JSON_DELETE_DEPRECATED_FUNCTIONS 0
+```
+
+## Notes
+
+!!! info "CMake option"
+
+    The macro can also be set with the CMake option
+    [`JSON_DeleteDeprecatedFunctions`](../../integration/cmake.md#json_deletedeprecatedfunctions) (`OFF` by default).
+
+!!! warning "Opt-in only"
+
+    This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no
+    effect. Define it for the whole project to avoid different declarations of the same class in different
+    translation units.
+
+!!! note "ABI compatibility"
+
+    The macro only turns calls that compile into calls that do not; it does not change the layout or the behavior of
+    any type. Its value is therefore not encoded in the [namespace](../../features/namespace.md).
+
+## Examples
+
+??? example "Example: default behavior (macro not defined)"
+
+    Without the macro, the deprecated overload is called, and the compiler warns about it:
+
+    ```cpp
+    #include <nlohmann/json.hpp>
+
+    using json = nlohmann::json;
+
+    int main()
+    {
+        const std::vector<std::uint8_t> v = {0x82, 0x01, 0x02};
+        auto j = json::from_cbor(v.data(), v.size());
+        // warning: 'from_cbor' is deprecated: Since 3.8.0; use from_cbor(ptr, ptr + len)
+    }
+    ```
+
+??? example "Example: deleted deprecated functions (macro defined to 1)"
+
+    With the macro, the call does not compile:
+
+    ```cpp
+    #define JSON_DELETE_DEPRECATED_FUNCTIONS 1
+    #include <nlohmann/json.hpp>
+
+    using json = nlohmann::json;
+
+    int main()
+    {
+        const std::vector<std::uint8_t> v = {0x82, 0x01, 0x02};
+        auto j = json::from_cbor(v.data(), v.size());
+        // error: call to deleted function 'from_cbor'
+    }
+    ```
+
+## See also
+
+- [Roadmap: removal of deprecated functions](../../community/roadmap.md#removal-of-deprecated-functions) - the
+  deprecated functions and the version they were deprecated in
+- [Migration guide: replace deprecated functions](../../integration/migration_guide.md#replace-deprecated-functions) -
+  how to replace each deprecated function
+
+## Version history
+
+- Added in version 3.13.0.
+- Planned to be removed in version 4.0.0, which removes the deprecated functions. The deprecated `from_*(ptr, len)`
+  overloads stay deleted in version 4.0.0.
@@ -112,3 +112,4 @@ The default value is `0` (disabled — existing behavior is preserved).
 ## Version history

 - Added in version 3.13.0.
+- Planned to become the default (with the macro removed) in version 4.0.0.
@@ -44,7 +44,7 @@ By default, implicit conversions are enabled.

 ## Examples

-??? example "Example: implicit conversion"
+??? example "Example: implicit and explicit conversions"

    This is an example for an implicit conversion:

@@ -0,0 +1,139 @@
+# JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+
+```cpp
+#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS /* value */
+```
+
+When defined to `1`, maps whose keys are enums (such as `std::map<E, T>` or `std::unordered_map<E, T>`) are stored as
+JSON objects, using the enum's own conversion for the keys. By default, they are stored as arrays of `[key, value]`
+pairs.
+
+## Default definition
+
+The default value is `0` (disabled — existing behavior is preserved).
+
+```cpp
+#define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 0
+```
+
+## Notes
+
+!!! note "Background"
+
+    JSON object keys are strings, so a map is only stored as an object if its keys can be converted to a string type.
+    Enums are not, even if [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) maps them to strings, so a
+    map with enum keys becomes an array of `[key, value]` pairs:
+
+    ```json
+    [["stopped", "aa"], ["completed", "bb"]]
+    ```
+
+    With this macro, the same map becomes an object
+    (see [#4378](https://github.com/nlohmann/json/issues/4378)):
+
+    ```json
+    {"completed": "bb", "stopped": "aa"}
+    ```
+
+!!! note "Maps with non-unique keys"
+
+    Maps that allow duplicate keys, such as `std::multimap<E, T>` or `std::unordered_multimap<E, T>`, are not affected
+    by the macro and are still stored as arrays of `[key, value]` pairs, as an object cannot hold duplicate keys.
+
+!!! note "Reading"
+
+    Reading is not affected by the macro: a map with enum keys can always be read from both an array of pairs and an
+    object. For the latter, each key is converted to the enum with its `from_json` function, e.g., the one defined by
+    [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md). Data written without the macro can therefore
+    still be read after enabling it.
+
+!!! warning "Keys must serialize to distinct strings"
+
+    Each key is converted with the enum's `to_json` function. If a key is not converted to a string (for instance, an
+    enum without [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md), which is stored as an integer, or an
+    enumerator mapped to `nullptr`), [`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) is thrown.
+    If two keys are converted to the same string (for instance, because
+    [`NLOHMANN_JSON_SERIALIZE_ENUM`](nlohmann_json_serialize_enum.md) maps an unlisted enumerator to the first entry),
+    [`type_error.318`](../../home/exceptions.md#jsonexceptiontype_error318) is thrown. In both cases, the target value
+    is not changed.
+
+!!! warning "Opt-in only"
+
+    This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no effect.
+
+!!! note "ABI compatibility"
+
+    The value of this macro is encoded in the [namespace](../../features/namespace.md) (tag `_ekmo`), resulting in
+    distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program
+    without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.
+
+## Examples
+
+??? example "Example: default behavior (macro not defined)"
+
+    Without the macro, a map with enum keys is stored as an array of pairs:
+
+    ```cpp
+    #include <map>
+    #include <nlohmann/json.hpp>
+
+    using json = nlohmann::json;
+
+    enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
+
+    NLOHMANN_JSON_SERIALIZE_ENUM(TaskState, {
+        {TS_STOPPED, "stopped"},
+        {TS_RUNNING, "running"},
+        {TS_COMPLETED, "completed"},
+    })
+
+    int main()
+    {
+        std::map<TaskState, std::string> m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
+
+        json j = m;
+        // j is [["stopped","aa"],["completed","bb"]]
+    }
+    ```
+
+??? example "Example: objects for enum-keyed maps (macro defined to 1)"
+
+    With the macro, the same map is stored as an object:
+
+    ```cpp
+    #define JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS 1
+    #include <map>
+    #include <nlohmann/json.hpp>
+
+    using json = nlohmann::json;
+
+    enum TaskState { TS_STOPPED, TS_RUNNING, TS_COMPLETED };
+
+    NLOHMANN_JSON_SERIALIZE_ENUM(TaskState, {
+        {TS_STOPPED, "stopped"},
+        {TS_RUNNING, "running"},
+        {TS_COMPLETED, "completed"},
+    })
+
+    int main()
+    {
+        std::map<TaskState, std::string> m = {{TS_STOPPED, "aa"}, {TS_COMPLETED, "bb"}};
+
+        json j = m;
+        // j is {"completed":"bb","stopped":"aa"}
+
+        auto m2 = j.get<std::map<TaskState, std::string>>();
+        // m2 == m
+    }
+    ```
+
+## See also
+
+- [Specializing enum conversion](../../features/enum_conversion.md)
+- [**NLOHMANN_JSON_SERIALIZE_ENUM**](nlohmann_json_serialize_enum.md) - serialize/deserialize an enum
+- [**NLOHMANN_JSON_SERIALIZE_ENUM_STRICT**](nlohmann_json_serialize_enum_strict.md) - serialize/deserialize an enum with
+  exceptions
+
+## Version history
+
+- Added in version 3.13.0.
@@ -41,6 +41,9 @@ inline void from_json(const BasicJsonType& j, type& e);
      conversion. Select this default pair carefully. See example 1 below.
    - If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
      list will be returned when converting to or from JSON. See example 2 below.
+    - Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default.
+      Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
+      with the converted keys. Such maps can be read from both forms.

 ## Examples

@@ -80,6 +83,7 @@ inline void from_json(const BasicJsonType& j, type& e);
 - [Specializing enum conversion](../../features/enum_conversion.md)
 - [`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](./nlohmann_json_serialize_enum_strict.md)
 - [`JSON_DISABLE_ENUM_SERIALIZATION`](json_disable_enum_serialization.md)
+- [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md)

 ## Version history

@@ -44,6 +44,9 @@ inline void from_json(const BasicJsonType& j, type& e);
      `"enum value out of range for <type>"`.
    - If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
      list will be returned when converting to or from JSON. See example 2 below.
+    - Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default.
+      Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
+      with the converted keys. Such maps can be read from both forms.

 ## Examples

@@ -99,6 +102,7 @@ inline void from_json(const BasicJsonType& j, type& e);
 - [Specializing enum conversion](../../features/enum_conversion.md)
 - [`NLOHMANN_JSON_SERIALIZE_ENUM`](./nlohmann_json_serialize_enum.md)
 - [`JSON_DISABLE_ENUM_SERIALIZATION`](json_disable_enum_serialization.md)
+- [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md)

 ## Version history

@@ -8,16 +8,16 @@ This type preserves the insertion order of object keys.

 ## Iterator invalidation

-The type is based on [`ordered_map`](ordered_map/index.md) which in turn uses a `std::vector` to store object elements.
+The type is based on [`ordered_map`](ordered_map.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/index.md) has no lookup index: every key-based object operation is a linear scan, so building or
+[`ordered_map`](ordered_map.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/index.md#complexity) for the per-operation table and for measured numbers.
+[`ordered_map` complexity](ordered_map.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/index.md)
+- [ordered_map](ordered_map.md)
 - [Object Order](../features/object_order.md)

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

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

 ## Member functions

- [(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)
+- (constructor)
+- (destructor)
+- **emplace**
+- **operator\[\]**
+- **at**
+- **erase**
+- **count**
+- **find**
+- **insert**

 ## Exception safety

@@ -90,7 +89,7 @@ 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
@@ -107,7 +106,7 @@ 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
    [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map)
    ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)), as the object type -- see
-    [object order](../../features/object_order.md).
+    [object order](../features/object_order.md).

 ## Examples

@@ -127,10 +126,10 @@ 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.
@@ -1,28 +0,0 @@
-# <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).
@@ -1,61 +0,0 @@
-# <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.
@@ -1,53 +0,0 @@
-# <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.
@@ -1,58 +0,0 @@
-# <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.
@@ -1,75 +0,0 @@
-# <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.
@@ -1,56 +0,0 @@
-# <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.
@@ -1,63 +0,0 @@
-# <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).
@@ -1,34 +0,0 @@
-# <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.
@@ -1,32 +0,0 @@
-# <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).
@@ -1,62 +0,0 @@
-# <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.
@@ -1,66 +0,0 @@
-# <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).
@@ -1,17 +0,0 @@
-# <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).
@@ -21,17 +21,18 @@ Note: Some modern features (like C++20 ranges or filesystem support) may be disa
      
        | Compiler                                     | Architecture | Operating System                  | CI        |
        |----------------------------------------------|--------------|-----------------------------------|-----------|
-        | AppleClang 15.0.0.15000040; Xcode 15.0.1     | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000100; Xcode 15.1       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000100; Xcode 15.2       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000309; Xcode 15.3       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
-        | AppleClang 15.0.0.15000309; Xcode 15.4       | arm64        | macOS 14.7.2 (Sonoma)             | GitHub    |
        | AppleClang 16.0.0.16000026; Xcode 16         | arm64        | macOS 15.2 (Sequoia)              | GitHub    |
        | AppleClang 16.0.0.16000026; Xcode 16.1       | arm64        | macOS 15.2 (Sequoia)              | GitHub    |
        | AppleClang 16.0.0.16000026; Xcode 16.2       | arm64        | macOS 15.2 (Sequoia)              | GitHub    |
        | AppleClang 17.0.0.17000013; Xcode 16.3       | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
        | AppleClang 17.0.0.17000013; Xcode 16.4       | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
        | AppleClang 17.0.0.17000319; Xcode 26.0.1     | arm64        | macOS 15.5 (Sequoia)              | GitHub    |
+        | AppleClang 17.0.0.17000404; Xcode 26.1.1     | arm64        | macOS 15.7.9 (Sequoia)            | GitHub    |
+        | AppleClang 17.0.0.17000603; Xcode 26.2       | arm64        | macOS 15.7.9 (Sequoia)            | GitHub    |
+        | AppleClang 17.0.0.17000604; Xcode 26.3       | arm64        | macOS 15.7.9 (Sequoia)            | GitHub    |
+        | AppleClang 21.0.0.21000099; Xcode 26.4.1     | arm64        | macOS 26.6.2 (Tahoe)              | GitHub    |
+        | AppleClang 21.0.0.21000101; Xcode 26.5       | arm64        | macOS 26.6.2 (Tahoe)              | GitHub    |
+        | AppleClang 21.0.0.21000101; Xcode 26.6       | arm64        | macOS 26.6.2 (Tahoe)              | GitHub    |
        | Clang 3.4.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | Clang 3.5.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | Clang 3.6.2                                  | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
@@ -89,7 +90,7 @@ Note: Some modern features (like C++20 ranges or filesystem support) may be disa
        | GNU 13.3.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | GNU 14.2.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | GNU 15.1.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
-        | GNU 16.1.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
+        | GNU 16.2.0                                   | x86_64       | Ubuntu 22.04.1 LTS                | GitHub    |
        | GNU 16.1.0                                   | arm64        | Ubuntu 24.04                      | GitHub    |
        | icpc (ICC) 2021.10.0 20230609                | x86_64       | Ubuntu 22.04 LTS                  | GitHub    |
        | icpx (Intel oneAPI DPC++/C++) 2025.3.2       | x86_64       | Ubuntu 24.04 LTS                  | GitHub    |
@@ -25,9 +25,7 @@ work items are tracked in the [GitHub milestones](https://github.com/nlohmann/js

 ## What the project will not do

- **Break the public API of version 3.x.** See the
-  [contribution guidelines](https://github.com/nlohmann/json/blob/develop/.github/CONTRIBUTING.md#break-the-public-api)
-  for what counts as a breaking change.
+- **Break the public API of version 3.x.** See [API stability](#api-stability) for what this covers.
 - **Require a newer C++ standard than C++11.**
 - **Break JSON conformance** or enable non-standard extensions by default.
 - **Add dependencies** or require a build step. The library remains header-only, and the single header
@@ -35,6 +33,32 @@ work items are tracked in the [GitHub milestones](https://github.com/nlohmann/js
 - **Trade simplicity for speed or memory efficiency.** Performance improvements are welcome, but the library is not
  meant to compete with the fastest JSON libraries, see [Design goals](../home/design_goals.md).

+## API stability
+
+Releases follow [semantic versioning](https://semver.org): a minor or patch release of version 3.x does not break code
+that uses the public API. In particular, a 3.x release does not:
+
+- change the signature of a function (its parameter types, return type, number of parameters, or the const-ness of a
+  member function);
+- remove or rename a function or class;
+- change which exceptions a function throws, or the [exception ids](../home/exceptions.md);
+- change access specifiers or default arguments.
+
+Exceptions to these rules, for instance when fixing a bug requires changing the exception a function throws, are
+documented in the [release notes](../home/releases.md).
+
+The following are **not** part of the public API and may change in any release, including patch releases:
+
+- The text of exception messages returned by `what()`. Use the [exception id](../home/exceptions.md) to tell errors
+  apart.
+- The ABI, including `sizeof(basic_json)` and the memory layout of its values. Recompile your code when you upgrade the
+  library. The [versioned inline namespace](../features/namespace.md) turns mixing versions into a link error.
+- Everything in namespace `nlohmann::detail`, and macros and type traits that are not documented in the
+  [API reference](../api/basic_json/index.md).
+
+Changes that would break the public API are only added behind a macro whose default keeps the 3.x behavior, see
+[Version 4.0](#version-40).
+
 ## Version 4.0

 There is no release date for version 4.0 yet. Proposals that need a major version, for instance stricter type
@@ -64,6 +88,8 @@ The following macros guard changes that are planned to become the default in ver
 | [`JSON_PRECISE_STREAM_POSITION`](../api/macros/json_precise_stream_position.md)                                  | `0`         | `1`: reading from a stream does not consume the character after a number                                                      | –                                                                                                                  | 3.13.0 |
 | [`JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md)                                          | `0`         | `1`: a NUL byte in the input is a parse error instead of the end of input                                                     | [`JSON_StrictNulHandling`](../integration/cmake.md#json_strictnulhandling)                                         | 3.13.0 |
 | [`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md)                                            | `0`         | `1`: `to_cbor`, `to_ubjson`, `to_bjdata`, and `to_bson` throw for strings that are not valid UTF-8 by default                 | [`JSON_StrictBinaryUTF8`](../integration/cmake.md#json_strictbinaryutf8)                                           | 3.13.0 |
+| [`JSON_DISABLE_TUPLE_REFERENCE_CONVERSION`](../api/macros/json_disable_tuple_reference_conversion.md)            | `0`         | `1`: a `basic_json` value can no longer be created from a one-element tuple of a reference to it, such as `std::forward_as_tuple(j)`| [`JSON_DisableTupleReferenceConversion`](../integration/cmake.md#json_disabletuplereferenceconversion)             | 3.13.0 |
+| [`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md)                          | `0`         | removed: the deprecated functions are removed (see below); the `from_*(ptr, len)` overloads stay deleted                      | [`JSON_DeleteDeprecatedFunctions`](../integration/cmake.md#json_deletedeprecatedfunctions)                         | 3.13.0 |

 For example, the following makes a 3.x release behave like version 4.0 with respect to these changes:

@@ -75,6 +101,8 @@ For example, the following makes a 3.x release behave like version 4.0 with resp
 #define JSON_PRECISE_STREAM_POSITION 1
 #define JSON_STRICT_NUL_HANDLING 1
 #define JSON_STRICT_BINARY_UTF8 1
+#define JSON_DISABLE_TUPLE_REFERENCE_CONVERSION 1
+#define JSON_DELETE_DEPRECATED_FUNCTIONS 1
 #include <nlohmann/json.hpp>
 ```

@@ -84,8 +112,13 @@ way to achieve this.
 ### Removal of deprecated functions

 Version 4.0 will remove all deprecated functions. Compiling with deprecation warnings enabled shows which of them your
-code still uses. The [migration guide](../integration/migration_guide.md#replace-deprecated-functions) shows how to
-replace each of them.
+code still uses. Defining [`JSON_DELETE_DEPRECATED_FUNCTIONS`](../api/macros/json_delete_deprecated_functions.md) to
+`1` turns these warnings into errors, as the deprecated functions are then deleted. The
+[migration guide](../integration/migration_guide.md#replace-deprecated-functions) shows how to replace each of them.
+
+The `from_*` overloads taking a pointer and a length are not removed in version 4.0, but stay deleted. Without them, a
+call like `from_cbor(ptr, len)` would still compile: it would read `ptr` as a NUL-terminated string and convert `len`
+to the `strict` parameter.

 | Deprecated                                                                                                                                                                                                                                         | Since  | Migration                                                                        |
 |----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|----------------------------------------------------------------------------------|
@@ -97,6 +130,7 @@ replace each of them.
 | [`json_pointer::operator string_t`](../api/json_pointer/operator_string_t.md)                                                                                                                                                                      | 3.11.0 | [JSON Pointers](../integration/migration_guide.md#json-pointers)                 |
 | [`json_pointer`](../api/json_pointer/index.md) with a `basic_json` type as template argument, and the overloads of `value`, `contains`, `operator[]`, and `at` accepting such a pointer                                                           | 3.11.0 | [JSON Pointers](../integration/migration_guide.md#json-pointers)                 |
 | Comparing a [`json_pointer`](../api/json_pointer/index.md) with a string via [`operator==`](../api/json_pointer/operator_eq.md) or [`operator!=`](../api/json_pointer/operator_ne.md)                                                              | 3.11.2 | [JSON Pointers](../integration/migration_guide.md#json-pointers)                 |
+| [`from_bjdata`](../api/basic_json/from_bjdata.md) and [`from_bon8`](../api/basic_json/from_bon8.md) with `(ptr, len)`                                                                                                                              | 3.13.0 | [Parsing](../integration/migration_guide.md#parsing)                             |

 The deprecated legacy comparison of discarded values is controlled by a macro and therefore listed in the table above.

@@ -1,21 +0,0 @@
-#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;
-}
@@ -1,2 +0,0 @@
-draft2 size: 4
-draft3 size: 6
@@ -1,11 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-true
@@ -1,10 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-true
@@ -1,13 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-["a",1,2.0,false]
@@ -13,19 +13,7 @@ class visitor_adaptor_with_metadata
    void do_visit(const Ptr& ptr, const Fnc& fnc) const;
 };

-using json = nlohmann::basic_json <
-             std::map,
-             std::vector,
-             std::string,
-             bool,
-             std::int64_t,
-             std::uint64_t,
-             double,
-             std::allocator,
-             nlohmann::adl_serializer,
-             std::vector<std::uint8_t>,
-             visitor_adaptor_with_metadata
-             >;
+using json = nlohmann::json::with_base_class_t<visitor_adaptor_with_metadata>;

 template <class Fnc>
 void visitor_adaptor_with_metadata::visit(const Fnc& fnc) const
@@ -1,10 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-true
@@ -1,10 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-true
@@ -1,10 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-true
@@ -1,10 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-true
@@ -1,10 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-true
@@ -1,10 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-true
@@ -1,12 +0,0 @@
-#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;
-}
@@ -1 +0,0 @@
-Container is std::vector<std::pair<const Key, T>>: true
				`@@ -1 +0,0 @@`
				`Container is std::vector<std::pair<const Key, T>>: true`