Merge branch 'develop' into guard-page-tests

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Fix AppVeyor failures from the Zmij double writer (#5843 )
2026-10-15 18:57:13 +00:00 · 2026-10-15 20:19:29 +02:00 · 2026-10-15 20:08:12 +02:00 · 2026-10-15 20:08:10 +02:00 · 2026-10-15 20:05:49 +02:00 · 2026-10-15 20:05:39 +02:00
63 changed files with 6590 additions and 1600 deletions
@@ -28,7 +28,7 @@ jobs:

    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -22,7 +22,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -31,7 +31,7 @@ jobs:
          mkdir -p ./pr
          echo ${{ github.event.number }} > ./pr/number
          echo ${{ github.event.pull_request.user.login }} > ./pr/author
-      - uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+      - uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
        with:
          name: pr
          path: pr/
@@ -46,7 +46,7 @@ jobs:

    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -170,7 +170,7 @@ jobs:
      # instead of installing the pinned astyle version locally.
      - name: Upload patch
        if: steps.diff.outputs.has_diff == 'true'
-        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
        with:
          name: amalgamation-patch
          path: patch/amalgamation.patch
@@ -20,7 +20,7 @@ jobs:
    timeout-minutes: 30
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -13,7 +13,7 @@ jobs:
    runs-on: ubuntu-22.04
    steps:
    - name: Harden Runner
-      uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+      uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
      with:
        egress-policy: audit

@@ -35,7 +35,7 @@ jobs:
        dry-run: false
        language: c++
    - name: Upload Crash
-      uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+      uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
      if: failure() && steps.build.outcome == 'success'
      with:
        name: artifacts
@@ -27,7 +27,7 @@ jobs:

    steps:
    - name: Harden Runner
-      uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+      uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
      with:
        egress-policy: audit

@@ -38,14 +38,14 @@ jobs:

    # Initializes the CodeQL tools for scanning.
    - name: Initialize CodeQL
-      uses: github/codeql-action/init@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+      uses: github/codeql-action/init@24c54180a607b1449ed407dd24f251e4e9147c8d # v4.38.3
      with:
        languages: c-cpp

    # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
    # If this step fails, then you should remove it and run the build manually (see below)
    - name: Autobuild
-      uses: github/codeql-action/autobuild@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+      uses: github/codeql-action/autobuild@24c54180a607b1449ed407dd24f251e4e9147c8d # v4.38.3

    - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+      uses: github/codeql-action/analyze@24c54180a607b1449ed407dd24f251e4e9147c8d # v4.38.3
@@ -20,7 +20,7 @@ jobs:
      pull-requests: write
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -21,7 +21,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -31,7 +31,7 @@ jobs:
      security-events: write
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -47,6 +47,6 @@ jobs:
          output: 'flawfinder_results.sarif'

      - name: Upload analysis results to GitHub Security tab
-        uses: github/codeql-action/upload-sarif@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+        uses: github/codeql-action/upload-sarif@24c54180a607b1449ed407dd24f251e4e9147c8d # v4.38.3
        with:
          sarif_file: ${{github.workspace}}/flawfinder_results.sarif
@@ -23,7 +23,7 @@ jobs:

    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -37,7 +37,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -40,7 +40,7 @@ jobs:

    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -72,7 +72,7 @@ jobs:
      # Upload the results as artifacts (optional). Commenting out will disable uploads of run results in SARIF
      # format to the repository Actions tab.
      - name: "Upload artifact"
-        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
        with:
          name: SARIF file
          path: results.sarif
@@ -80,6 +80,6 @@ jobs:

      # Upload the results to GitHub's code scanning dashboard.
      - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+        uses: github/codeql-action/upload-sarif@24c54180a607b1449ed407dd24f251e4e9147c8d # v4.38.3
        with:
          sarif_file: results.sarif
@@ -36,7 +36,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -65,7 +65,7 @@ jobs:

      # Upload SARIF file generated in previous step
      - name: Upload SARIF file
-        uses: github/codeql-action/upload-sarif@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+        uses: github/codeql-action/upload-sarif@24c54180a607b1449ed407dd24f251e4e9147c8d # v4.38.3
        with:
          sarif_file: semgrep.sarif
        if: always()
@@ -16,7 +16,7 @@ jobs:

    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -25,7 +25,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -38,7 +38,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Check that Meson and pkg-config offer the CMake options
        run: make check_build_options
      - name: Install Meson
@@ -80,7 +80,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -92,14 +92,14 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
        run: cmake --build build --target ci_infer
      - name: Archive Infer report
        if: always()
-        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
        with:
          name: infer-report
          path: ${{ github.workspace }}/build/build_infer/infer-out/report.txt
@@ -112,7 +112,7 @@ jobs:
        target: [ci_test_single_header, ci_cppcheck, ci_cpplint, ci_reproducible_tests, ci_non_git_tests, ci_offline_testdata, ci_reuse_compliance, ci_test_valgrind]
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -123,7 +123,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -142,7 +142,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -168,7 +168,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -178,7 +178,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -197,7 +197,7 @@ jobs:
      - name: Build
        run: cmake --build build --target ci_test_coverage
      - name: Archive coverage report
-        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
        with:
          name: code-coverage-report
          path: ${{ github.workspace }}/build/html
@@ -244,7 +244,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: CXX=g++-${{ matrix.compiler }} cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -262,7 +262,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -279,7 +279,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Disable filesystem support (std::filesystem is unusable) for clang 7 / 8 / 9 / 10
        run: echo "JSON_FORCED_GLOBAL_COMPILE_OPTIONS=-DJSON_HAS_FILESYSTEM=0;-DJSON_HAS_EXPERIMENTAL_FILESYSTEM=0" >> "$GITHUB_ENV"
        if: ${{ matrix.compiler == '7' || matrix.compiler == '8' || matrix.compiler == '9' || matrix.compiler == '10' }}
@@ -299,7 +299,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -319,7 +319,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build with libc++
@@ -346,7 +346,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -366,7 +366,7 @@ jobs:
      # import-std support. Its opt-in token is CMake-version-specific, so pin
      # CMake to the version whose token is set in tests/module_cpp20/CMakeLists.txt.
      - name: Get pinned CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
        with:
          cmakeVersion: 4.3.4
      # Clang: the std library module is provided by libc++ (the image's libstdc++
@@ -392,7 +392,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -409,7 +409,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -423,7 +423,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DJSON_CI=On
      - name: Build
@@ -433,7 +433,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -443,7 +443,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Run CMake
        run: cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=$EMSDK/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -GNinja
      - name: Build
@@ -456,7 +456,7 @@ jobs:
        target: [ci_test_examples, ci_test_build_documentation, ci_test_documentation_mermaid]
    steps:
      - name: Harden Runner
-        uses: step-security/harden-runner@351661ca32ac09a36dc5ee2d536e3128f2a3c8ed # v2.22.0
+        uses: step-security/harden-runner@ccd8616d44fd3846e67624a50d5aad6d37bf2d25 # v2.22.1
        with:
          egress-policy: audit

@@ -465,7 +465,7 @@ jobs:
          persist-credentials: false
          # the git-revision-date-localized plugin needs the history; a shallow clone makes the strict build fail
          fetch-depth: ${{ matrix.target == 'ci_test_build_documentation' && '0' || '1' }}
-      - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+      - uses: actions/setup-node@949feb2413d6458794dcd2491c4babbbce0c15c1 # v7.1.0
        if: matrix.target == 'ci_test_documentation_mermaid'
        with:
          node-version: 24
@@ -484,7 +484,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Check that the job runs natively on arm64
        run: uname -m && test "$(uname -m)" = aarch64
      - name: Run CMake
@@ -90,7 +90,7 @@ jobs:
        with:
          persist-credentials: false
      - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
      - name: Set extra CXX_FLAGS for latest std_version
        # /wd5285 silences C5285 emitted by the bundled third-party doctest.h, which
        # specializes std::tuple (newly diagnosed by the VS2026 v145 toolset)
@@ -214,7 +214,7 @@ jobs:
      # import-std support. Its opt-in token is CMake-version-specific, so pin
      # CMake to the version whose token is set in tests/module_cpp20/CMakeLists.txt.
      - name: Get pinned CMake and ninja
-        uses: lukka/get-cmake@fffaaafeea488556c2c12dad60690008bc1caacb # v4.4.2
+        uses: lukka/get-cmake@a89e43e22a96abafcd7a62db652a65ecd33052c9 # v4.4.4
        with:
          cmakeVersion: 4.3.4
      # CMAKE_CXX_FLAGS replaces CMake's MSVC defaults (which include /EHsc), and
@@ -485,6 +485,13 @@ add_custom_target(ci_clang_analyze
 # Check code with Cppcheck.
 ###############################################################################

+# default_defines.hpp expands the Hedley macros to the compiler's feature-test operators, which Cppcheck does not know.
+# Since Cppcheck 2.20, it rejects their invocations in #if conditions instead of evaluating them as 0.
+file(WRITE ${CMAKE_BINARY_DIR}/cppcheck_feature_tests.hpp "")
+foreach(OPERATOR __has_attribute __has_builtin __has_cpp_attribute __has_declspec_attribute __has_extension __has_feature __has_include __has_warning)
+    file(APPEND ${CMAKE_BINARY_DIR}/cppcheck_feature_tests.hpp "#define ${OPERATOR}(x) 0\n")
+endforeach()
+
 add_custom_target(ci_cppcheck
    COMMAND mkdir -p cppcheck
    COMMAND clang -dM -E -x c++ -std=c++11 ${CMAKE_SOURCE_DIR}/include/nlohmann/thirdparty/hedley/hedley.hpp > default_defines.hpp 2> /dev/null
@@ -493,7 +500,7 @@ add_custom_target(ci_cppcheck
    COMMAND venv_cppcheck/bin/cppcheck --enable=warning --check-level=exhaustive --inline-suppr --inconclusive --force
            --std=c++11 ${PROJECT_SOURCE_DIR}/include/nlohmann/json.hpp -I ${CMAKE_SOURCE_DIR}/include
            --error-exitcode=1 --relative-paths=${PROJECT_SOURCE_DIR} -j ${N} --include=default_defines.hpp
-            --cppcheck-build-dir=cppcheck
+            --include=${CMAKE_BINARY_DIR}/cppcheck_feature_tests.hpp --cppcheck-build-dir=cppcheck
            -UJSON_CATCH_USER -UJSON_TRY_USER -UJSON_ASSERT -UJSON_INTERNAL_CATCH -UJSON_THROW
            -DJSON_HAS_CPP_11 -UJSON_HAS_CPP_14 -UJSON_HAS_CPP_17 -UJSON_HAS_CPP_20 -UJSON_HAS_THREE_WAY_COMPARISON
    COMMENT "Check code with Cppcheck"
@@ -1 +1 @@
-cppcheck==1.5.1
+cppcheck==1.5.2
@@ -68,6 +68,14 @@ basic_json(basic_json&& other) noexcept;
     `std::unordered_map`, `std::multimap`, and `std::unordered_multimap` with a `key_type` compatible to `string_t`
     and a `value_type` from which a `basic_json` value can be constructed.
    - **strings**: `string_t`, string literals, and all compatible string containers can be used.
+
+    !!! note "Rvalue containers are moved from"
+
+        If `val` is an rvalue of a compatible array-like or object-like container other than `array_t`/`object_t`
+        (e.g., `json j = std::move(vec);` or `json j(std::vector<std::string>{...});`), the elements are moved into
+        the JSON value instead of copied. Afterwards, the elements of the source container are in a valid but
+        unspecified state (**moved-from**). Keys of associative containers are `const` and therefore still copied.
+        Lvalues and `const` rvalues are copied, and the source is left unchanged.
    - **numbers**: [`number_integer_t`](number_integer_t.md), [`number_unsigned_t`](number_unsigned_t.md),
     [`number_float_t`](number_float_t.md), and all convertible number types such as `int`, `size_t`, `int64_t`, `float`
     or `double` can be used.
@@ -236,7 +244,9 @@ basic_json(basic_json&& other) noexcept;
 2. No-throw guarantee: this constructor never throws exceptions.
 3. Depends on the called constructor. For types directly supported by the library (i.e., all types for which no
   `to_json()` function was provided), a strong guarantee holds: if an exception is thrown, there are no changes to any
-   JSON value.
+   JSON value. **Exception:** when `val` is an rvalue array-like or object-like container, its elements are moved one
+   by one; if an exception is thrown in the middle of the conversion (e.g., an allocation failure), the JSON value is
+   unchanged, but the source container may be left partially moved-from.
 4. Depends on the called constructor. For types directly supported by the library (i.e., all types for which no
   `to_json()` function was provided), a strong guarantee holds: if an exception is thrown, there are no changes to any
   JSON value.
@@ -6,6 +6,9 @@ constexpr bool is_number_unsigned() const noexcept;

 This function returns `#!cpp true` if and only if the JSON value is an unsigned integer number. This excludes
 floating-point and signed integer values.
+
+If [`number_unsigned_t`](number_unsigned_t.md) is the same type as [`number_integer_t`](number_integer_t.md), every
+integer is stored as `number_integer_t`, and this function always returns `#!cpp false`.
    
 ## Return value

@@ -25,7 +25,8 @@ the type to use.
 `NumberUnsignedType`
 :   the type to store unsigned integers. It must be an **unsigned integral** type (`#!cpp std::is_integral`) with a
    `#!cpp std::numeric_limits` specialization, and it must be able to represent the absolute value of every
-    [`number_integer_t`](number_integer_t.md) value. See
+    [`number_integer_t`](number_integer_t.md) value. Alternatively, it can be the same type as
+    [`number_integer_t`](number_integer_t.md); then every integer is stored as `number_integer_t`. See
    [Template Parameter Requirements](../../features/types/template_parameters.md#numberintegertype-and-numberunsignedtype).

 ## Notes
@@ -89,3 +90,4 @@ Integer number values are stored directly inside a `basic_json` type.
 ## Version history

 - Added in version 2.0.0.
+- Can be the same type as `number_integer_t` since version 3.13.0.
@@ -345,8 +345,11 @@ The number types can be changed with template parameters.
      in case of overflow.
    - The type for unsigned integers must be convertible from `#!c unsigned long long`.  The type for floating-point
      numbers is used in case of overflow.
-    - The types for signed and unsigned integers must be distinct, see
-      [#2573](https://github.com/nlohmann/json/issues/2573).
+    - The type for unsigned integers can also be the same signed type as the type for signed integers (e.g.,
+      `#!c std::int64_t` for both). Then every integer is stored as a signed integer, and
+      [`is_number_unsigned()`](../../api/basic_json/is_number_unsigned.md) is always `#!c false`, see
+      [Template Parameter Requirements](template_parameters.md#same-type-for-both).
+    - The type for floating-point numbers must be distinct from the integer types.
    - Only `#!c double`, `#!c float`, and `#!c long double` are supported for floating-point numbers.

 !!! example
@@ -40,19 +40,19 @@ Requirements are split into two groups:

 ## Overview

-| Template parameter                                                | Default                           | Notable substitutes                                                   |
-|-------------------------------------------------------------------|-----------------------------------|-----------------------------------------------------------------------|
-| [`ObjectType`](#objecttype)                                       | `std::map`                        | [`nlohmann::ordered_map`](../../api/ordered_map.md), Abseil hash maps |
-| [`ArrayType`](#arraytype)                                         | `std::vector`                     | `#!cpp std::deque`                                                    |
-| [`StringType`](#stringtype)                                       | `std::string`                     | `std::string`-like types over `char`                                  |
-| [`BooleanType`](#booleantype)                                     | `bool`                            | none worth using                                                      |
-| [`NumberIntegerType`](#numberintegertype-and-numberunsignedtype)  | `std::int64_t`                    | any signed integer type                                               |
-| [`NumberUnsignedType`](#numberintegertype-and-numberunsignedtype) | `std::uint64_t`                   | any unsigned integer type at least as wide as `NumberIntegerType`     |
-| [`NumberFloatType`](#numberfloattype)                             | `double`                          | `float` (`long double`: no binary formats)                            |
-| [`AllocatorType`](#allocatortype)                                 | `std::allocator`                  | stateless allocators                                                  |
-| [`JSONSerializer`](#jsonserializer)                               | `adl_serializer`                  | serializers with the same interface                                   |
-| [`BinaryType`](#binarytype)                                       | `#!cpp std::vector<std::uint8_t>` | `#!cpp std::vector<char>`                                             |
-| [`CustomBaseClass`](#custombaseclass)                             | `void`                            | any default-constructible class                                       |
+| Template parameter                                                | Default                           | Notable substitutes                                                                              |
+|-------------------------------------------------------------------|-----------------------------------|--------------------------------------------------------------------------------------------------|
+| [`ObjectType`](#objecttype)                                       | `std::map`                        | [`nlohmann::ordered_map`](../../api/ordered_map.md), Abseil hash maps                            |
+| [`ArrayType`](#arraytype)                                         | `std::vector`                     | `#!cpp std::deque`                                                                               |
+| [`StringType`](#stringtype)                                       | `std::string`                     | `std::string`-like types over `char`                                                             |
+| [`BooleanType`](#booleantype)                                     | `bool`                            | none worth using                                                                                 |
+| [`NumberIntegerType`](#numberintegertype-and-numberunsignedtype)  | `std::int64_t`                    | any signed integer type                                                                          |
+| [`NumberUnsignedType`](#numberintegertype-and-numberunsignedtype) | `std::uint64_t`                   | any unsigned integer type at least as wide as `NumberIntegerType`, or `NumberIntegerType` itself |
+| [`NumberFloatType`](#numberfloattype)                             | `double`                          | `float` (`long double`: no binary formats)                                                       |
+| [`AllocatorType`](#allocatortype)                                 | `std::allocator`                  | stateless allocators                                                                             |
+| [`JSONSerializer`](#jsonserializer)                               | `adl_serializer`                  | serializers with the same interface                                                              |
+| [`BinaryType`](#binarytype)                                       | `#!cpp std::vector<std::uint8_t>` | `#!cpp std::vector<char>`                                                                        |
+| [`CustomBaseClass`](#custombaseclass)                             | `void`                            | any default-constructible class                                                                  |

 !!! warning "Third-party containers and incomplete types"

@@ -504,13 +504,14 @@ Both types are stored **directly** inside `basic_json`'s union.
 ### Always required

 - `#!cpp std::is_integral` must be satisfied: `NumberIntegerType` must be a **signed** integer type,
-  `NumberUnsignedType` an **unsigned** integer type. Class types are not supported -- among others, the constructors
-  taking integer values are constrained on `#!cpp std::is_integral`.
+  `NumberUnsignedType` an **unsigned** integer type or the same type as `NumberIntegerType` (see
+  [below](#same-type-for-both)). Class types are not supported -- among others, the constructors taking integer values
+  are constrained on `#!cpp std::is_integral`.
 - Trivially default-constructible, trivially copyable, and trivially destructible (union member).
 - `#!cpp std::numeric_limits` must be specialized for both types.
- `NumberUnsignedType` must be able to represent the absolute value of every `NumberIntegerType` value; serialization
-  of negative numbers converts the value to `NumberUnsignedType`. A `#!cpp static_assert` requires it to be at least as
-  wide as `NumberIntegerType`, which is what that amounts to for the standard integer types.
+- An unsigned `NumberUnsignedType` must be able to represent the absolute value of every `NumberIntegerType` value;
+  serialization of negative numbers converts the value to `NumberUnsignedType`. A `#!cpp static_assert` requires it to
+  be at least as wide as `NumberIntegerType`, which is what that amounts to for the standard integer types.
 - Both types must fit into the internal 64-character number buffer used by
  [`dump`](../../api/basic_json/dump.md), which is the case for all standard integer types.
 - [`std::hash<basic_json>`](../../api/basic_json/std_hash.md) additionally requires `#!cpp std::hash` specializations.
@@ -522,6 +523,23 @@ is stored as [`number_float_t`](../../api/basic_json/number_float_t.md) instead.
 therefore silently changes parse results rather than raising an error. See
 [Number Handling](number_handling.md) for details.

+#### Same type for both
+
+`NumberUnsignedType` may be the same type as `NumberIntegerType`, e.g.
+`#!cpp nlohmann::json::with_integers_t<std::int64_t, std::int64_t>` (see
+[`with_integers_t`](../../api/basic_json/with_t.md)), for code that only wants to handle one integer type. Such a `basic_json` stores every integer as
+[`number_integer_t`](../../api/basic_json/number_integer_t.md):
+
+- [`is_number_unsigned()`](../../api/basic_json/is_number_unsigned.md) is always `#!cpp false`, and
+  [`type()`](../../api/basic_json/type.md) never returns `value_t::number_unsigned`. Constructing a value from
+  `value_t::number_unsigned` gives a `value_t::number_integer` value.
+- Values of unsigned C++ types (e.g., `#!cpp 5u`) are converted to `NumberIntegerType`, so values above its maximum
+  wrap around, as values outside the range of a narrower `NumberIntegerType` already do.
+- The parsers store a non-negative integer above the maximum of `NumberIntegerType` (e.g., `18446744073709551615` for
+  `#!cpp std::int64_t`) as [`number_float_t`](../../api/basic_json/number_float_t.md), like any other integer that does
+  not fit.
+- Converting from a `basic_json` with distinct types turns its unsigned values into `number_integer_t` values.
+
 ### Compatible types

 | Type pair                                                                                    | Support                                                                                                                                                                                          |
@@ -529,8 +547,9 @@ therefore silently changes parse results rather than raising an error. See
 | `#!cpp std::int64_t` / `#!cpp std::uint64_t` (default)                                       | full                                                                                                                                                                                             |
 | `#!cpp std::int32_t` / `#!cpp std::uint32_t`, `#!cpp long long` / `#!cpp unsigned long long` | full; narrower types change which literals the parser can represent                                                                                                                              |
 | any other pair of standard signed/unsigned integer types                                     | full                                                                                                                                                                                             |
+| the same signed integer type for both, e.g. `#!cpp std::int64_t` / `#!cpp std::int64_t`      | full; every integer is stored as `number_integer_t`, see [above](#same-type-for-both)                                                                                                            |
 | class types, enumerations                                                                    | not usable; `#!cpp std::is_integral` must hold                                                                                                                                                   |
-| `#!cpp bool`, or a type already used for another member of the union                         | not usable; `#!cpp std::is_integral<bool>` is in fact `#!cpp true`, but the `get_impl_ptr` overloads for `boolean_t`, `number_integer_t`, `number_unsigned_t` and `number_float_t` would collide |
+| `#!cpp bool`, `number_float_t`, or the type of another member of the union                  | not usable; `#!cpp std::is_integral<bool>` is in fact `#!cpp true`, but the `get_impl_ptr` overloads for `boolean_t`, `number_integer_t`, `number_unsigned_t` and `number_float_t` would collide |

 ## `NumberFloatType`

@@ -9,6 +9,15 @@ published on the [GitHub releases page](https://github.com/nlohmann/json/release
    This documentation is built from the `develop` branch and may describe changes that are not part of a release
    yet. Their version numbers are followed by an <span class="unreleased-version">unreleased</span> badge.

+## Unreleased
+
+- Converting an rvalue container to JSON (`json j = std::move(vec);`, `json j = std::map<std::string, std::string>{...};`)
+  now **moves** the elements instead of copying them (e.g., `std::vector<std::string>` with 100,000 strings: 4.7 ms to
+  2.3 ms). Two consequences: the source container is left in a valid but unspecified (moved-from) state, and if an
+  exception is thrown during the conversion, the source may be partially moved-from, so the strong exception guarantee
+  no longer holds for the source of an rvalue conversion (the JSON value itself is unaffected). Lvalues and `const`
+  objects are still copied. See [`basic_json`](../api/basic_json/basic_json.md).
+
 ## v3.12.0 (2025-04-11)

 Fixes bugs found in 3.11.3 and adds several features. All changes are backward-compatible.
@@ -80,7 +80,11 @@ void get_arithmetic_value(const BasicJsonType& j, ArithmeticType& val)
    {
        case value_t::number_unsigned:
        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>());
+            // never null: a basic_json whose number_unsigned_t is number_integer_t
+            // stores no number_unsigned values (#2573)
+            const auto* ptr = j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>();
+            JSON_ASSERT(ptr != nullptr);
+            val = static_cast<ArithmeticType>(*ptr);
            break;
        }
        case value_t::number_integer:
@@ -150,7 +154,7 @@ inline void from_json(const BasicJsonType& j, typename BasicJsonType::number_flo
 }

 template<typename BasicJsonType>
-inline void from_json(const BasicJsonType& j, typename BasicJsonType::number_unsigned_t& val)
+inline void from_json(const BasicJsonType& j, number_unsigned_overload_t<BasicJsonType>& val)
 {
    get_arithmetic_value(j, val);
 }
@@ -266,6 +270,22 @@ template<typename ConstructibleArrayType>
 void from_json_array_reserve(ConstructibleArrayType& /*arr*/, std::size_t /*size*/, priority_tag<0> /*unused*/)
 {}

+// append through push_back() where available; containers without it (such as
+// std::set) fall back to insert(end(), ...), which is what std::inserter did
+template<typename ConstructibleArrayType, typename ValueType>
+auto from_json_array_append(ConstructibleArrayType& arr, ValueType&& value, priority_tag<1> /*unused*/)
+-> decltype(arr.push_back(std::forward<ValueType>(value)), void())
+{
+    arr.push_back(std::forward<ValueType>(value));
+}
+
+template<typename ConstructibleArrayType, typename ValueType>
+void from_json_array_append(ConstructibleArrayType& arr, ValueType&& value, priority_tag<0> /*unused*/)
+{
+    using std::end;
+    arr.insert(end(arr), std::forward<ValueType>(value));
+}
+
 template<typename BasicJsonType, typename ConstructibleArrayType,
         enable_if_t<
             std::is_assignable<ConstructibleArrayType&, ConstructibleArrayType>::value,
@@ -275,17 +295,15 @@ auto from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr, p
    j.template get<typename ConstructibleArrayType::value_type>(),
    void())
 {
-    using std::end;
-
    ConstructibleArrayType ret;
-    from_json_array_reserve(ret, j.size(), priority_tag<1> {});
-    std::transform(j.begin(), j.end(),
-                   std::inserter(ret, end(ret)), [](const BasicJsonType & i)
+    const auto* inner_array = j.template get_ptr<const typename BasicJsonType::array_t*>();
+    from_json_array_reserve(ret, inner_array->size(), priority_tag<1> {});
+    for (const auto& elem : *inner_array)
    {
        // get<BasicJsonType>() returns *this, this won't call a from_json
        // method when value_type is BasicJsonType
-        return i.template get<typename ConstructibleArrayType::value_type>();
-    });
+        from_json_array_append(ret, elem.template get<typename ConstructibleArrayType::value_type>(), priority_tag<1> {});
+    }
    arr = std::move(ret);
 }

@@ -371,6 +389,23 @@ template<typename ConstructibleObjectType>
 inline void from_json_object_reserve(ConstructibleObjectType& /*obj*/, std::size_t /*size*/, priority_tag<0> /*unused*/)
 {}

+// the keys of the source are sorted for the usual object types, so hinting the
+// end makes every insertion constant-time (for containers that order their keys
+// the same way); containers without emplace_hint() (such as ordered_map) fall
+// back to emplace()
+template<typename ConstructibleObjectType, typename Key, typename Value>
+auto from_json_object_emplace(ConstructibleObjectType& obj, Key&& key, Value&& value, priority_tag<1> /*unused*/)
+-> decltype(obj.emplace_hint(obj.end(), std::forward<Key>(key), std::forward<Value>(value)), void())
+{
+    obj.emplace_hint(obj.end(), std::forward<Key>(key), std::forward<Value>(value));
+}
+
+template<typename ConstructibleObjectType, typename Key, typename Value>
+void from_json_object_emplace(ConstructibleObjectType& obj, Key&& key, Value&& value, priority_tag<0> /*unused*/)
+{
+    obj.emplace(std::forward<Key>(key), std::forward<Value>(value));
+}
+
 template<typename BasicJsonType, typename ConstructibleObjectType,
         enable_if_t<is_constructible_object_type<BasicJsonType, ConstructibleObjectType>::value, int> = 0>
 inline void from_json(const BasicJsonType& j, ConstructibleObjectType& obj)
@@ -385,7 +420,7 @@ inline void from_json(const BasicJsonType& j, ConstructibleObjectType& obj)
    from_json_object_reserve(ret, inner_object->size(), priority_tag<1> {});
    for (const auto& p : *inner_object)
    {
-        ret.emplace(p.first, p.second.template get<typename ConstructibleObjectType::mapped_type>());
+        from_json_object_emplace(ret, p.first, p.second.template get<typename ConstructibleObjectType::mapped_type>(), priority_tag<1> {});
    }
    obj = std::move(ret);
 }
@@ -406,7 +441,11 @@ inline void from_json(const BasicJsonType& j, ArithmeticType& val)
    {
        case value_t::number_unsigned:
        {
-            val = static_cast<ArithmeticType>(*j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>());
+            // never null: a basic_json whose number_unsigned_t is number_integer_t
+            // stores no number_unsigned values (#2573)
+            const auto* ptr = j.template get_ptr<const typename BasicJsonType::number_unsigned_t*>();
+            JSON_ASSERT(ptr != nullptr);
+            val = static_cast<ArithmeticType>(*ptr);
            break;
        }
        case value_t::number_integer:
@@ -167,6 +167,17 @@ struct external_constructor<value_t::array>
        j.replace_value(value_t::array, value);
    }

+    /// an rvalue container: move its elements
+    template<typename BasicJsonType, typename CompatibleArrayType>
+    static void construct_moving(BasicJsonType& j, CompatibleArrayType& arr)
+    {
+        using std::begin;
+        using std::end;
+
+        const typename BasicJsonType::json_value value(j.template create<typename BasicJsonType::array_t>(std::make_move_iterator(begin(arr)), std::make_move_iterator(end(arr))));
+        j.replace_value(value_t::array, value);
+    }
+
    template<typename BasicJsonType>
    static void construct(BasicJsonType& j, const std::vector<bool>& arr)
    {
@@ -217,6 +228,17 @@ struct external_constructor<value_t::object>
        j.replace_value(value_t::object, value);
    }

+    /// an rvalue container: move its values
+    template<typename BasicJsonType, typename CompatibleObjectType>
+    static void construct_moving(BasicJsonType& j, CompatibleObjectType& obj)
+    {
+        using std::begin;
+        using std::end;
+
+        const typename BasicJsonType::json_value value(j.template create<typename BasicJsonType::object_t>(std::make_move_iterator(begin(obj)), std::make_move_iterator(end(obj))));
+        j.replace_value(value_t::object, value);
+    }
+
    template < typename BasicJsonType, typename CompatibleObjectType,
               enable_if_t < !std::is_same<CompatibleObjectType, typename BasicJsonType::object_t>::value, int > = 0 >
    static void construct(BasicJsonType& j, const CompatibleObjectType& obj)
@@ -303,14 +325,14 @@ inline void to_json(BasicJsonType& j, FloatType val) noexcept
 }

 template<typename BasicJsonType, typename CompatibleNumberUnsignedType,
-         enable_if_t<is_compatible_integer_type<typename BasicJsonType::number_unsigned_t, CompatibleNumberUnsignedType>::value, int> = 0>
+         enable_if_t<is_compatible_integer_type<number_unsigned_overload_t<BasicJsonType>, CompatibleNumberUnsignedType>::value, int> = 0>
 inline void to_json(BasicJsonType& j, CompatibleNumberUnsignedType val) noexcept
 {
    external_constructor<value_t::number_unsigned>::construct(j, static_cast<typename BasicJsonType::number_unsigned_t>(val));
 }

 template<typename BasicJsonType, typename CompatibleNumberIntegerType,
-         enable_if_t<is_compatible_integer_type<typename BasicJsonType::number_integer_t, CompatibleNumberIntegerType>::value, int> = 0>
+         enable_if_t<is_compatible_number_integer_type<BasicJsonType, CompatibleNumberIntegerType>::value, int> = 0>
 inline void to_json(BasicJsonType& j, CompatibleNumberIntegerType val) noexcept
 {
    external_constructor<value_t::number_integer>::construct(j, static_cast<typename BasicJsonType::number_integer_t>(val));
@@ -354,6 +376,66 @@ inline void to_json(BasicJsonType& j, const CompatibleArrayType& arr)
    external_constructor<value_t::array>::construct(j, arr);
 }

+// types that have a dedicated to_json overload and must not be treated as generic containers
+template<typename T>
+struct has_dedicated_to_json : std::false_type {};
+
+#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
+template<>
+struct has_dedicated_to_json<std_fs::path> : std::true_type {};
+#endif
+
+#if defined(__cpp_lib_char8_t)
+template<typename Tr, typename Allocator>
+struct has_dedicated_to_json<std::basic_string<char8_t, Tr, Allocator>> : std::true_type {};
+#endif
+
+#if JSON_HAS_RANGE_VIEW_CONVERSION
+template<typename T>
+struct is_range_view_type : is_compatible_range_view<T> {};
+#else
+template<typename T>
+struct is_range_view_type : std::false_type {};
+#endif
+
+#if JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
+template<typename T>
+struct is_enum_keyed_map_type : is_enum_keyed_map<T> {};
+#else
+template<typename T>
+struct is_enum_keyed_map_type : std::false_type {};
+#endif
+
+// rvalue (non-const) container: the generic to_json takes its elements by move
+template<typename T>
+using is_movable_container_rvalue = negation<disjunction<
+                                    std::is_lvalue_reference<T>,
+                                    std::is_const<T>,
+                                    has_dedicated_to_json<T>,
+                                    is_basic_json<T>,
+                                    is_range_view_type<T>,
+                                    is_enum_keyed_map_type<T>,
+                                    std::is_same<T, std::vector<bool>>>>;
+
+// rvalue array-like containers
+template<typename BasicJsonType, typename T>
+using is_rvalue_array_to_json = conjunction<is_movable_container_rvalue<T>,
+      is_compatible_array_type<BasicJsonType, T>,
+      negation<disjunction<
+      std::is_same<T, typename BasicJsonType::array_t>,
+      std::is_same<T, typename BasicJsonType::binary_t>,
+      is_compatible_object_type<BasicJsonType, T>,
+      is_compatible_string_type<BasicJsonType, T>,
+      is_compatible_binary_type<BasicJsonType, T>>>>;
+
+// rvalue containers: their elements are moved instead of copied
+template<typename BasicJsonType, typename CompatibleArrayType,
+         enable_if_t<is_rvalue_array_to_json<BasicJsonType, CompatibleArrayType>::value, int> = 0>
+inline void to_json(BasicJsonType& j, CompatibleArrayType && arr)
+{
+    external_constructor<value_t::array>::construct_moving(j, arr);
+}
+
 #if JSON_HAS_RANGE_VIEW_CONVERSION
 template < typename BasicJsonType, typename T,
           enable_if_t < is_compatible_range_view<std::remove_cvref_t<T>>::value
@@ -427,6 +509,19 @@ inline void to_json(BasicJsonType& j, const EnumKeyedMap& map)
 }
 #endif

+// rvalue object-like containers
+template<typename BasicJsonType, typename T>
+using is_rvalue_object_to_json = conjunction<is_movable_container_rvalue<T>,
+      negation<std::is_same<T, typename BasicJsonType::object_t>>,
+      is_compatible_object_type<BasicJsonType, T>>;
+
+template<typename BasicJsonType, typename CompatibleObjectType,
+         enable_if_t<is_rvalue_object_to_json<BasicJsonType, CompatibleObjectType>::value, int> = 0>
+inline void to_json(BasicJsonType& j, CompatibleObjectType && obj)
+{
+    external_constructor<value_t::object>::construct_moving(j, obj);
+}
+
 template<typename BasicJsonType>
 inline void to_json(BasicJsonType& j, typename BasicJsonType::object_t&& obj)
 {
@@ -184,7 +184,10 @@ JSON_HEDLEY_ALWAYS_INLINE shortest_decimal to_shortest(std::uint64_t bits) noexc
    const uint128_parts p10 = pow10(-dec_exp - 1);
    const uint128_parts p = umul192_hi128(p10.high, p10.low, bin_sig << static_cast<unsigned>(shift));
    std::uint64_t integral = p.high >> static_cast<unsigned>(extra_shift);
-    const std::uint64_t fractional = (p.high << static_cast<unsigned>(64 - extra_shift)) | (p.low >> static_cast<unsigned>(extra_shift));
+    // (no casts in the shifts: MSVC 2015 warns C4554 on them despite the parentheses)
+    constexpr unsigned fractional_low_shift = static_cast<unsigned>(extra_shift);
+    constexpr unsigned fractional_high_shift = 64u - fractional_low_shift;
+    const std::uint64_t fractional = (p.high << fractional_high_shift) | (p.low >> fractional_low_shift);
    std::uint64_t digit = 0;
    bool round_up = false;
    bool round_down = false;
@@ -428,7 +428,7 @@ void templated_json_throw(ExceptionType exception)
@throw type_error.302 always
 */
 template<typename BasicJsonType>
-JSON_HEDLEY_NO_RETURN inline void throw_type_must_be(const char* expected, const BasicJsonType& j)
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_type_must_be(const char* expected, const BasicJsonType& j)
 {
    static_cast<void>(expected); // unused when JSON_NOEXCEPTION is defined
    static_cast<void>(j);
@@ -443,7 +443,7 @@ JSON_HEDLEY_NO_RETURN inline void throw_type_must_be(const char* expected, const
@throw type_error always
 */
 template<typename BasicJsonType>
-JSON_HEDLEY_NO_RETURN inline void throw_cannot_use_with(const exception_id id_, const char* operation, const BasicJsonType& j)
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_cannot_use_with(const exception_id id_, const char* operation, const BasicJsonType& j)
 {
    static_cast<void>(id_); // unused when JSON_NOEXCEPTION is defined
    static_cast<void>(operation);
@@ -451,6 +451,77 @@ JSON_HEDLEY_NO_RETURN inline void throw_cannot_use_with(const exception_id id_,
    JSON_THROW(type_error::create(id_, concat("cannot use ", operation, " with ", j.type_name()), &j));
 }

+/*!
+@brief throws ExceptionType with a fixed message; kept out of line so that callers do not carry the exception construction
+*/
+template<typename ExceptionType, typename BasicJsonContext>
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_literal(const exception_id id_, const char* what_arg, BasicJsonContext context)
+{
+    static_cast<void>(id_); // unused when JSON_NOEXCEPTION is defined
+    static_cast<void>(what_arg);
+    static_cast<void>(context);
+    JSON_THROW(ExceptionType::create(id_, what_arg, context));
+}
+
+// JSON Patch errors; constructed out of line so that patch_inplace() does not carry them
+
+template<typename BasicJsonType>
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_patch_add_parent(const BasicJsonType& parent)
+{
+    static_cast<void>(parent);
+    JSON_THROW(out_of_range::create(exception_id::patch_add_parent_not_container, concat("cannot add value: the JSON Patch 'add' target's parent is of type ", parent.type_name(), ", but must be an object or array"), &parent));
+}
+
+template<typename BasicJsonType>
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_patch_remove_parent(const BasicJsonType& parent)
+{
+    static_cast<void>(parent);
+    JSON_THROW(out_of_range::create(exception_id::patch_remove_parent_not_container, concat("cannot remove value: the JSON Patch 'remove' target's parent is of type ", parent.type_name(), ", but must be an object or array"), &parent));
+}
+
+template<typename BasicJsonType>
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_patch_not_an_array(const BasicJsonType& j)
+{
+    static_cast<void>(j);
+    JSON_THROW(parse_error::create(exception_id::patch_not_an_array, 0, "JSON patch must be an array of objects", &j));
+}
+
+template<typename StringType, typename BasicJsonType>
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_patch_missing_member(const StringType& op, const StringType& member, const bool string_type, const BasicJsonType& val)
+{
+    static_cast<void>(op);
+    static_cast<void>(member);
+    static_cast<void>(string_type);
+    static_cast<void>(val);
+    // context-sensitive error message
+    const std::string error_msg = (op == "op") ? std::string("operation") : concat("operation '", op, '\'');
+    JSON_THROW(parse_error::create(exception_id::patch_invalid_operation, 0, concat(error_msg, string_type ? " must have string member '" : " must have member '", member, "'"), &val));
+}
+
+template<typename StringType, typename BasicJsonType>
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_patch_move_into_child(const StringType& from_path, const StringType& path, const BasicJsonType& result)
+{
+    static_cast<void>(from_path);
+    static_cast<void>(path);
+    static_cast<void>(result);
+    JSON_THROW(out_of_range::create(exception_id::patch_move_into_child, concat("cannot move value: 'from' path '", from_path, "' is a proper prefix of 'path' '", path, "'"), &result));
+}
+
+template<typename BasicJsonType>
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_patch_test_failed(const BasicJsonType& val)
+{
+    static_cast<void>(val);
+    JSON_THROW(other_error::create(exception_id::patch_test_failed, concat("unsuccessful: ", val.dump()), &val));
+}
+
+template<typename StringType, typename BasicJsonType>
+JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_patch_invalid_operation(const StringType& op, const BasicJsonType& val)
+{
+    static_cast<void>(op);
+    static_cast<void>(val);
+    JSON_THROW(parse_error::create(exception_id::patch_invalid_operation, 0, concat("operation value '", op, "' is invalid"), &val));
+}
+
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END

@@ -195,7 +195,7 @@ class binary_reader

            if (JSON_HEDLEY_UNLIKELY(current != char_traits<char_type>::eof()))
            {
-                return last_byte_error(exception_id::unexpected_end_of_input, concat("expected end of input; last byte: 0x", get_token_string()), "value");
+                return last_byte_error(exception_id::unexpected_end_of_input, "expected end of input", "value", "");
            }
        }

@@ -317,7 +317,7 @@ class binary_reader
    {
        if (JSON_HEDLEY_UNLIKELY(document_size < 0 || static_cast<std::size_t>(document_size) != chars_read - document_start))
        {
-            return last_byte_error(exception_id::unexpected_byte, concat("document size ", std::to_string(document_size), " does not match the number of bytes read (", std::to_string(chars_read - document_start), ")"), "document");
+            return bson_document_size_error(document_size, chars_read - document_start);
        }
        return true;
    }
@@ -509,7 +509,7 @@ class binary_reader
    {
        if (JSON_HEDLEY_UNLIKELY(len < 1))
        {
-            return last_byte_error(exception_id::unexpected_byte, concat("string length must be at least 1, is ", std::to_string(len)), "string");
+            return bson_length_error("string length must be at least 1, is ", len, "string");
        }

        if (JSON_HEDLEY_UNLIKELY(!get_string(len - static_cast<NumberType>(1), result)))
@@ -539,7 +539,7 @@ class binary_reader
    {
        if (JSON_HEDLEY_UNLIKELY(len < 0))
        {
-            return last_byte_error(exception_id::unexpected_byte, concat("byte array length cannot be negative, is ", std::to_string(len)), "binary");
+            return bson_length_error("byte array length cannot be negative, is ", len, "binary");
        }

        // All BSON binary values have a subtype
@@ -629,9 +629,7 @@ class binary_reader

            default: // anything else is not supported (yet)
            {
-                const std::string cr_str = hex_byte(static_cast<std::uint8_t>(element_type));
-                return sax->parse_error(element_type_parse_position, cr_str,
-                                        parse_error::create(exception_id::bson_unsupported_type, element_type_parse_position, concat("Unsupported BSON record type 0x", cr_str), nullptr));
+                return bson_unsupported_type_error(element_type_parse_position, element_type);
            }
        }
    }
@@ -1060,6 +1058,7 @@ class binary_reader
    @param[in] context  parsing context for the error message
    @return whether the SAX consumer accepts the parse error
    */
+    JSON_HEDLEY_NEVER_INLINE
    bool cbor_indefinite_string_error(const char* type_name, const char* context)
    {
        return last_byte_error(exception_id::invalid_string_or_size, concat("indefinite-length ", type_name, " is not allowed inside indefinite-length ", type_name, "; last byte: 0x", get_token_string()), context);
@@ -1139,7 +1138,7 @@ class binary_reader

            default:
            {
-                return last_byte_error(exception_id::invalid_string_or_size, concat("expected length specification (0x60-0x7B)", inside_indefinite ? "" : " or indefinite string type (0x7F)", "; last byte: 0x", get_token_string()), "string");
+                return last_byte_error(exception_id::invalid_string_or_size, "expected length specification (0x60-0x7B)", "string", inside_indefinite ? "" : " or indefinite string type (0x7F)");
            }
        }
    }
@@ -1269,7 +1268,7 @@ class binary_reader
                break;
        }

-        return last_byte_error(exception_id::invalid_string_or_size, concat("only string keys are supported, but found ", found, "; last byte: 0x", get_token_string()), "object key");
+        return last_byte_error(exception_id::invalid_string_or_size, "only string keys are supported, but found ", "object key", found);
    }

    /*!
@@ -1350,7 +1349,7 @@ class binary_reader

            default:
            {
-                return last_byte_error(exception_id::invalid_string_or_size, concat("expected length specification (0x40-0x5B)", inside_indefinite ? "" : " or indefinite binary array type (0x5F)", "; last byte: 0x", get_token_string()), "binary");
+                return last_byte_error(exception_id::invalid_string_or_size, "expected length specification (0x40-0x5B)", "binary", inside_indefinite ? "" : " or indefinite binary array type (0x5F)");
            }
        }
    }
@@ -1496,8 +1495,7 @@ class binary_reader
    {
        if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::size_t>(len) || len == detail::unknown_size()))
        {
-            return sax->parse_error(chars_read, get_token_string(), out_of_range::create(exception_id::container_too_large,
-                                    exception_message(concat("excessive ", context, " size"), "size"), nullptr));
+            return container_size_error(context);
        }
        result = conditional_static_cast<std::size_t>(len);
        return true;
@@ -2065,7 +2063,7 @@ class binary_reader

            default:
            {
-                return last_byte_error(exception_id::invalid_string_or_size, concat("expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0x", get_token_string()), "string");
+                return last_byte_error(exception_id::invalid_string_or_size, "expected length specification (0xA0-0xBF, 0xD9-0xDB)", "string", "");
            }
        }
    }
@@ -2157,7 +2155,7 @@ class binary_reader
                break;
        }

-        return last_byte_error(exception_id::invalid_string_or_size, concat("only string keys are supported, but found ", found, "; last byte: 0x", get_token_string()), "object key");
+        return last_byte_error(exception_id::invalid_string_or_size, "only string keys are supported, but found ", "object key", found);
    }

    /*!
@@ -2655,8 +2653,7 @@ class binary_reader
        }
        if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::size_t>(number)))
        {
-            return sax->parse_error(chars_read, get_token_string(), out_of_range::create(exception_id::container_too_large,
-                                    exception_message("integer value overflow", "size"), nullptr));
+            return out_of_range_error(exception_id::container_too_large, "integer value overflow", "size");
        }
        result = static_cast<std::size_t>(number); // NOLINT(bugprone-signed-char-misuse,cert-str34-c): number is not a char
        return true;
@@ -2753,8 +2750,7 @@ class binary_reader
                }
                if (!value_in_range_of<std::size_t>(number))
                {
-                    return sax->parse_error(chars_read, get_token_string(), out_of_range::create(exception_id::container_too_large,
-                                            exception_message("integer value overflow", "size"), nullptr));
+                    return out_of_range_error(exception_id::container_too_large, "integer value overflow", "size");
                }
                result = detail::conditional_static_cast<std::size_t>(number);
                return true;
@@ -2832,7 +2828,7 @@ class binary_reader
                        // or SIZE_MAX.
                        if (JSON_HEDLEY_UNLIKELY(result > (std::numeric_limits<std::size_t>::max)() / i))
                        {
-                            return sax->parse_error(chars_read, get_token_string(), out_of_range::create(exception_id::container_too_large, exception_message("excessive ndarray size caused overflow", "size"), nullptr));
+                            return out_of_range_error(exception_id::container_too_large, "excessive ndarray size caused overflow", "size");
                        }
                        result *= i;
                        // the pre-check above already rules out result becoming 0
@@ -2841,7 +2837,7 @@ class binary_reader
                        // unknown-size container (see get_ubjson_size_type())
                        if (result == npos)
                        {
-                            return sax->parse_error(chars_read, get_token_string(), out_of_range::create(exception_id::container_too_large, exception_message("excessive ndarray size caused overflow", "size"), nullptr));
+                            return out_of_range_error(exception_id::container_too_large, "excessive ndarray size caused overflow", "size");
                        }
                        if (JSON_HEDLEY_UNLIKELY(!emit_unsigned(i)))
                        {
@@ -2891,7 +2887,7 @@ class binary_reader
            if (input_format == input_format_t::bjdata
                    && JSON_HEDLEY_UNLIKELY(is_bjd_excluded_optimized_type(result.second)))
            {
-                return last_byte_error(exception_id::unexpected_byte, concat("marker 0x", get_token_string(), " is not a permitted optimized array type"), "type");
+                return optimized_type_error();
            }

            if (JSON_HEDLEY_UNLIKELY(!unexpect_eof("type")))
@@ -2906,7 +2902,7 @@ class binary_reader
                {
                    return false;
                }
-                return last_byte_error(exception_id::unexpected_byte, concat("expected '#' after type information; last byte: 0x", get_token_string()), "size");
+                return last_byte_error(exception_id::unexpected_byte, "expected '#' after type information", "size", "");
            }

            const bool is_error = get_ubjson_size_value(result.first, is_ndarray, 0, result.second);
@@ -3057,7 +3053,7 @@ class binary_reader
                }
                if (JSON_HEDLEY_UNLIKELY(current > 127))
                {
-                    return last_byte_error(exception_id::invalid_string_or_size, concat("byte after 'C' must be in range 0x00..0x7F; last byte: 0x", get_token_string()), "char");
+                    return last_byte_error(exception_id::invalid_string_or_size, "byte after 'C' must be in range 0x00..0x7F", "char", "");
                }
                string_t s(1, static_cast<typename string_t::value_type>(current));
                return sax->string(s);
@@ -3141,8 +3137,7 @@ class binary_reader
            if (JSON_HEDLEY_UNLIKELY((size_and_type.second == 'Z' || size_and_type.second == 'T' || size_and_type.second == 'F')
                                     && size_and_type.first > max_valueless_container_size))
            {
-                return sax->parse_error(chars_read, get_token_string(), out_of_range::create(exception_id::container_too_large,
-                                        exception_message("excessive array size", "size"), nullptr));
+                return out_of_range_error(exception_id::container_too_large, "excessive array size", "size");
            }

            if (JSON_HEDLEY_UNLIKELY(!enter_array(size_and_type.first, size_and_type.second)))
@@ -3854,7 +3849,7 @@ class binary_reader
        {
            // in case of failure, advance position by 1 to report the failing location
            ++chars_read;
-            sax->parse_error(chars_read, "<end of file>", parse_error::create(exception_id::unexpected_end_of_input, chars_read, exception_message("unexpected end of input", context), nullptr));
+            static_cast<void>(report_eof(context));
            return false;
        }
        return true;
@@ -4007,8 +4002,7 @@ class binary_reader
        const auto result = static_cast<number_float_t>(number);
        if (JSON_HEDLEY_UNLIKELY(std::isfinite(number) && !std::isfinite(result)))
        {
-            return sax->parse_error(chars_read, get_token_string(),
-                                    out_of_range::create(exception_id::number_overflow, exception_message("number overflow", "value"), nullptr));
+            return out_of_range_error(exception_id::number_overflow, "number overflow", "value");
        }
        return sax->number_float(result, "");
    }
@@ -4223,22 +4217,82 @@ class binary_reader
    {
        if (JSON_HEDLEY_UNLIKELY(current == char_traits<char_type>::eof()))
        {
-            return sax->parse_error(chars_read, "<end of file>",
-                                    parse_error::create(exception_id::unexpected_end_of_input, chars_read, exception_message("unexpected end of input", context), nullptr));
+            return report_eof(context);
        }
        return true;
    }

+    /*!
+    @brief reports an unexpected end of input (out of line to keep the exception
+           construction out of the hot reading functions)
+    @param[in] context  further context information (for diagnostics)
+    @return the result of the SAX parser's parse_error()
+    */
+    JSON_HEDLEY_NON_NULL(2)
+    JSON_HEDLEY_NEVER_INLINE
+    bool report_eof(const char* context) const
+    {
+        return sax->parse_error(chars_read, "<end of file>",
+                                parse_error::create(exception_id::unexpected_end_of_input, chars_read, exception_message("unexpected end of input", context), nullptr));
+    }
+
+    /*!
+    @brief reports an out_of_range error at the last read byte (out of line)
+    */
+    JSON_HEDLEY_NEVER_INLINE
+    bool out_of_range_error(const exception_id id_, const char* detail, const char* context) const
+    {
+        return sax->parse_error(chars_read, get_token_string(), out_of_range::create(id_, exception_message(detail, context), nullptr));
+    }
+
+    JSON_HEDLEY_NEVER_INLINE
+    bool container_size_error(const char* what) const
+    {
+        return sax->parse_error(chars_read, get_token_string(), out_of_range::create(exception_id::container_too_large,
+                                exception_message(concat("excessive ", what, " size"), "size"), nullptr));
+    }
+
+    JSON_HEDLEY_NEVER_INLINE
+    bool optimized_type_error() const
+    {
+        return last_byte_error(exception_id::unexpected_byte, concat("marker 0x", get_token_string(), " is not a permitted optimized array type"), "type");
+    }
+
+    template<typename NumberType>
+    JSON_HEDLEY_NEVER_INLINE
+    bool bson_length_error(const char* prefix, const NumberType len, const char* context) const
+    {
+        return last_byte_error(exception_id::unexpected_byte, concat(prefix, std::to_string(len)), context);
+    }
+
+    JSON_HEDLEY_NEVER_INLINE
+    bool bson_document_size_error(const std::int32_t document_size, const std::size_t bytes_read) const
+    {
+        return last_byte_error(exception_id::unexpected_byte, concat("document size ", std::to_string(document_size), " does not match the number of bytes read (", std::to_string(bytes_read), ")"), "document");
+    }
+
+    JSON_HEDLEY_NEVER_INLINE
+    bool bson_unsupported_type_error(const std::size_t position, const char element_type) const
+    {
+        const std::string cr_str = hex_byte(static_cast<std::uint8_t>(element_type));
+        return sax->parse_error(position, cr_str,
+                                parse_error::create(exception_id::bson_unsupported_type, position, concat("Unsupported BSON record type 0x", cr_str), nullptr));
+    }
+
    /*!
    @brief reports a parse error at the last read byte
    @param[in] id_      the id of the parse_error exception
    @param[in] detail   a detailed error message
    @param[in] context  further context information
+    @param[in] tail     optional text appended to the detail, followed by "; last byte: 0x<token>"
    @return the result of the SAX parser's parse_error()
    */
-    bool last_byte_error(const exception_id id_, const std::string& detail, const std::string& context) const
+    JSON_HEDLEY_NEVER_INLINE
+    bool last_byte_error(const exception_id id_, const std::string& detail, const char* context, const char* tail = nullptr) const
    {
-        return sax->parse_error(chars_read, get_token_string(), parse_error::create(id_, chars_read, exception_message(detail, context), nullptr));
+        // with a tail, the message reads "<detail><tail>; last byte: 0x<token>"
+        return sax->parse_error(chars_read, get_token_string(), parse_error::create(id_, chars_read,
+                                exception_message(tail == nullptr ? detail : concat(detail, tail, "; last byte: 0x", get_token_string()), context), nullptr));
    }

    /*!
@@ -4247,7 +4301,8 @@ class binary_reader
    @param[in] context  further context information
    @return the result of the SAX parser's parse_error()
    */
-    bool unexpected_byte(const char* detail, const std::string& context) const
+    JSON_HEDLEY_NEVER_INLINE
+    bool unexpected_byte(const char* detail, const char* context) const
    {
        return last_byte_error(exception_id::unexpected_byte, concat(detail, ": 0x", get_token_string()), context);
    }
@@ -4258,6 +4313,7 @@ class binary_reader
    @param[in] context   further context information
    @return the result of the SAX parser's parse_error()
    */
+    JSON_HEDLEY_NEVER_INLINE
    bool length_type_error(const char* position, const char* context) const
    {
        const char* types = input_format == input_format_t::bjdata ? "U, i, u, I, m, l, M, L" : "U, i, I, l, L";
@@ -187,12 +187,19 @@ Shared by json_sax_dom_parser and json_sax_dom_callback_parser.
@param[in] ref   the object or array that was just created
@return whether parsing should continue (false after reporting out_of_range.408)
 */
+template<typename SAX, typename BasicJsonType>
+JSON_HEDLEY_NEVER_INLINE
+bool container_too_large_error(SAX& sax, std::size_t len, const char* kind, BasicJsonType* ref)
+{
+    return sax.parse_error(0, "", out_of_range::create(exception_id::container_too_large, concat("excessive ", kind, " size: ", std::to_string(len)), ref));
+}
+
 template<typename SAX, typename BasicJsonType>
 bool check_container_size(SAX& sax, std::size_t len, const char* kind, BasicJsonType* ref)
 {
    if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref->max_size()))
    {
-        return sax.parse_error(0, "", out_of_range::create(exception_id::container_too_large, concat("excessive ", kind, " size: ", std::to_string(len)), ref));
+        return container_too_large_error(sax, len, kind, ref);
    }
    return true;
 }
@@ -674,16 +681,19 @@ class json_sax_dom_callback_parser
        if (keep && ref_stack.back())
        {
            auto& obj = *ref_stack.back()->m_data.m_value.object;
-            const auto it = obj.find(val);
-            if (it != obj.end())
+            // a single lookup: insert the placeholder, or find the existing member
+            const auto inserted = obj.emplace(val, discarded);
+            const auto it = inserted.first;
+            if (!inserted.second)
            {
                // this is a duplicate key (legal in JSON); remember its
                // current value so it can be restored later if the new
                // value is rejected by the callback, instead of being
                // erased together with the discarded placeholder
                duplicate_key_stash.emplace_back(&(it->second), it->second);
+                it->second = discarded;
            }
-            object_element = &(obj[val] = discarded);
+            object_element = &(it->second);
        }

        return true;
@@ -19,7 +19,7 @@
 #include <cstring> // memcpy
 #include <limits> // numeric_limits
 #include <string> // string
-#include <type_traits> // conditional, integral_constant, true_type, false_type
+#include <type_traits> // conditional, integral_constant, is_signed, true_type, false_type
 #include <utility> // move

 #include <nlohmann/detail/bit_ops.hpp>
@@ -50,6 +50,20 @@ NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
 {

+// whether an integer of a signed type is negative; the overload for other types
+// avoids comparing an unsigned value with zero
+template<typename NumberType>
+constexpr bool is_negative_integer(NumberType x, std::true_type /*is_signed*/) noexcept
+{
+    return x < 0;
+}
+
+template<typename NumberType>
+constexpr bool is_negative_integer(NumberType /*unused*/, std::false_type /*is_signed*/) noexcept
+{
+    return false;
+}
+
 /*!
@brief fast integer parser for an already-validated unsigned integer

@@ -83,8 +97,10 @@ bool parse_integer_unsigned(const char* first, const char* last, NumberUnsignedT
        x = (x * 10u) + digit;
    }
    value = static_cast<NumberUnsignedType>(x);
-    // reject values that do not round-trip into a narrower NumberUnsignedType
-    return static_cast<std::uint64_t>(value) == x;
+    // reject values that do not round-trip into a narrower NumberUnsignedType,
+    // and values that wrap around to negative numbers if it is a signed type
+    // (number_unsigned_t may be the same type as number_integer_t, #2573)
+    return static_cast<std::uint64_t>(value) == x && !is_negative_integer(value, std::is_signed<NumberUnsignedType>());
 }

 /*!
@@ -704,7 +720,7 @@ inline void float_from_bits(std::uint64_t bits, float& value) noexcept
 {
    static_assert(sizeof(float) == sizeof(std::uint32_t), "float must have 32 bits");
    const auto bits32 = static_cast<std::uint32_t>(bits);
-    std::memcpy(&value, &bits32, sizeof(value));
+    std::memcpy(&value, &bits32, sizeof(bits32));
 }

 /// the powers of ten that are exact in binary64 (up to 10^22)
@@ -280,7 +280,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    }

    /// @throw invalid_iterator.214 always
-    JSON_HEDLEY_NO_RETURN void throw_cannot_get_value() const
+    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE void throw_cannot_get_value() const
    {
        JSON_THROW(invalid_iterator::create(exception_id::iterator_value_unavailable, "cannot get value", m_object));
    }
@@ -294,40 +294,25 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    {
        JSON_ASSERT(m_object != nullptr);

-        switch (m_object->m_data.m_type)
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))
        {
-            case value_t::object:
-            {
-                JSON_ASSERT(m_it.object_iterator != m_object->m_data.m_value.object->end());
-                return m_it.object_iterator->second;
-            }
-
-            case value_t::array:
-            {
-                JSON_ASSERT(m_it.array_iterator != m_object->m_data.m_value.array->end());
-                return *m_it.array_iterator;
-            }
-
-            case value_t::null:
-                throw_cannot_get_value();
-
-            case value_t::string:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::binary:
-            case value_t::discarded:
-            default:
-            {
-                if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.is_begin()))
-                {
-                    return *m_object;
-                }
-
-                throw_cannot_get_value();
-            }
+            JSON_ASSERT(m_it.array_iterator != m_object->m_data.m_value.array->end());
+            return *m_it.array_iterator;
        }
+
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
+        {
+            JSON_ASSERT(m_it.object_iterator != m_object->m_data.m_value.object->end());
+            return m_it.object_iterator->second;
+        }
+
+        // neither array nor object: a primitive value (null has no value to point to)
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type != value_t::null && m_it.primitive_iterator.is_begin()))
+        {
+            return *m_object;
+        }
+
+        throw_cannot_get_value();
    }

    /*!
@@ -338,38 +323,25 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    {
        JSON_ASSERT(m_object != nullptr);

-        switch (m_object->m_data.m_type)
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))
        {
-            case value_t::object:
-            {
-                JSON_ASSERT(m_it.object_iterator != m_object->m_data.m_value.object->end());
-                return &(m_it.object_iterator->second);
-            }
-
-            case value_t::array:
-            {
-                JSON_ASSERT(m_it.array_iterator != m_object->m_data.m_value.array->end());
-                return &*m_it.array_iterator;
-            }
-
-            case value_t::null:
-            case value_t::string:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::binary:
-            case value_t::discarded:
-            default:
-            {
-                if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.is_begin()))
-                {
-                    return m_object;
-                }
-
-                throw_cannot_get_value();
-            }
+            JSON_ASSERT(m_it.array_iterator != m_object->m_data.m_value.array->end());
+            return &*m_it.array_iterator;
        }
+
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
+        {
+            JSON_ASSERT(m_it.object_iterator != m_object->m_data.m_value.object->end());
+            return &(m_it.object_iterator->second);
+        }
+
+        // neither array nor object: a primitive value
+        if (JSON_HEDLEY_LIKELY(m_it.primitive_iterator.is_begin()))
+        {
+            return m_object;
+        }
+
+        throw_cannot_get_value();
    }

    /*!
@@ -391,35 +363,20 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    {
        JSON_ASSERT(m_object != nullptr);

-        switch (m_object->m_data.m_type)
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))
        {
-            case value_t::object:
-            {
-                std::advance(m_it.object_iterator, 1);
-                break;
-            }
-
-            case value_t::array:
-            {
-                std::advance(m_it.array_iterator, 1);
-                break;
-            }
-
-            case value_t::null:
-            case value_t::string:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::binary:
-            case value_t::discarded:
-            default:
-            {
-                ++m_it.primitive_iterator;
-                break;
-            }
+            ++m_it.array_iterator;
+            return *this;
        }

+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
+        {
+            std::advance(m_it.object_iterator, 1);
+            return *this;
+        }
+
+        // neither array nor object: a primitive value
+        ++m_it.primitive_iterator;
        return *this;
    }

@@ -442,35 +399,20 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
    {
        JSON_ASSERT(m_object != nullptr);

-        switch (m_object->m_data.m_type)
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))
        {
-            case value_t::object:
-            {
-                std::advance(m_it.object_iterator, -1);
-                break;
-            }
-
-            case value_t::array:
-            {
-                std::advance(m_it.array_iterator, -1);
-                break;
-            }
-
-            case value_t::null:
-            case value_t::string:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::binary:
-            case value_t::discarded:
-            default:
-            {
-                --m_it.primitive_iterator;
-                break;
-            }
+            --m_it.array_iterator;
+            return *this;
        }

+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
+        {
+            std::advance(m_it.object_iterator, -1);
+            return *this;
+        }
+
+        // neither array nor object: a primitive value
+        --m_it.primitive_iterator;
        return *this;
    }

@@ -484,7 +426,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
        // if objects are not the same, the comparison is undefined
        if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
        {
-            JSON_THROW(invalid_iterator::create(exception_id::iterators_compare_different_values, "cannot compare iterators of different containers", m_object));
+            throw_literal<invalid_iterator>(exception_id::iterators_compare_different_values, "cannot compare iterators of different containers", m_object);
        }

        // value-initialized forward iterators can be compared, and must compare equal to other value-initialized iterators of the same type #4493
@@ -493,25 +435,18 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
            return true;
        }

-        switch (m_object->m_data.m_type)
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::array))
        {
-            case value_t::object:
-                return (m_it.object_iterator == other.m_it.object_iterator);
-
-            case value_t::array:
-                return (m_it.array_iterator == other.m_it.array_iterator);
-
-            case value_t::null:
-            case value_t::string:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::binary:
-            case value_t::discarded:
-            default:
-                return (m_it.primitive_iterator == other.m_it.primitive_iterator);
+            return (m_it.array_iterator == other.m_it.array_iterator);
        }
+
+        if (JSON_HEDLEY_LIKELY(m_object->m_data.m_type == value_t::object))
+        {
+            return (m_it.object_iterator == other.m_it.object_iterator);
+        }
+
+        // neither array nor object: a primitive value
+        return (m_it.primitive_iterator == other.m_it.primitive_iterator);
    }

    /*!
@@ -533,7 +468,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
        // if objects are not the same, the comparison is undefined
        if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
        {
-            JSON_THROW(invalid_iterator::create(exception_id::iterators_compare_different_values, "cannot compare iterators of different containers", m_object));
+            throw_literal<invalid_iterator>(exception_id::iterators_compare_different_values, "cannot compare iterators of different containers", m_object);
        }

        // value-initialized forward iterators can be compared, and must compare equal to other value-initialized iterators of the same type #4493
@@ -546,7 +481,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
        switch (m_object->m_data.m_type)
        {
            case value_t::object:
-                JSON_THROW(invalid_iterator::create(exception_id::iterator_order_on_object, "cannot compare order of object iterators", m_object));
+                throw_literal<invalid_iterator>(exception_id::iterator_order_on_object, "cannot compare order of object iterators", m_object);

            case value_t::array:
                return (m_it.array_iterator < other.m_it.array_iterator);
@@ -602,7 +537,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
        switch (m_object->m_data.m_type)
        {
            case value_t::object:
-                JSON_THROW(invalid_iterator::create(exception_id::iterator_arithmetic_on_object, "cannot use offsets with object iterators", m_object));
+                throw_literal<invalid_iterator>(exception_id::iterator_arithmetic_on_object, "cannot use offsets with object iterators", m_object);

            case value_t::array:
            {
@@ -681,7 +616,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
        switch (m_object->m_data.m_type)
        {
            case value_t::object:
-                JSON_THROW(invalid_iterator::create(exception_id::iterator_arithmetic_on_object, "cannot use offsets with object iterators", m_object));
+                throw_literal<invalid_iterator>(exception_id::iterator_arithmetic_on_object, "cannot use offsets with object iterators", m_object);

            case value_t::array:
                return m_it.array_iterator - other.m_it.array_iterator;
@@ -710,7 +645,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
        switch (m_object->m_data.m_type)
        {
            case value_t::object:
-                JSON_THROW(invalid_iterator::create(exception_id::iterator_subscript_on_object, "cannot use operator[] for object iterators", m_object));
+                throw_literal<invalid_iterator>(exception_id::iterator_subscript_on_object, "cannot use operator[] for object iterators", m_object);

            case value_t::array:
                return *std::next(m_it.array_iterator, n);
@@ -750,7 +685,7 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
            return m_it.object_iterator->first;
        }

-        JSON_THROW(invalid_iterator::create(exception_id::iterator_key_not_object, "cannot use key() for non-object iterators", m_object));
+        throw_literal<invalid_iterator>(exception_id::iterator_key_not_object, "cannot use key() for non-object iterators", m_object);
    }

    /*!
@@ -16,14 +16,13 @@
    #include <iosfwd> // ostream
 #endif  // JSON_NO_IO
 #include <limits> // max
-#include <map> // map
-#include <numeric> // accumulate
 #include <string> // string
 #include <utility> // move
 #include <vector> // vector

 #include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
+#include <nlohmann/detail/meta/cpp_future.hpp>
 #include <nlohmann/detail/string_concat.hpp>
 #include <nlohmann/detail/string_escape.hpp>
 #include <nlohmann/detail/string_utils.hpp>
@@ -69,12 +68,21 @@ class json_pointer
    /// @sa https://json.nlohmann.me/api/json_pointer/to_string/
    string_t to_string() const
    {
-        return std::accumulate(reference_tokens.begin(), reference_tokens.end(),
-                               string_t{},
-                               [](const string_t& a, const string_t& b)
+        // one buffer: every token adds its escaped form (at least its length) and a slash
+        std::size_t length = 0;
+        for (const auto& reference_token : reference_tokens)
        {
-            return detail::concat<string_t>(a, '/', detail::escape(b));
-        });
+            length += reference_token.size() + 1;
+        }
+
+        string_t result;
+        result.reserve(length);
+        for (const auto& reference_token : reference_tokens)
+        {
+            result.append("/", 1);
+            detail::escape_into(result, reference_token);
+        }
+        return result;
    }

    /// @brief return a string representation of the JSON pointer
@@ -129,21 +137,29 @@ class json_pointer
    friend json_pointer operator/(const json_pointer& lhs,
                                  const json_pointer& rhs)
    {
-        return json_pointer(lhs) /= rhs;
+        json_pointer result;
+        result.reference_tokens.reserve(lhs.reference_tokens.size() + rhs.reference_tokens.size());
+        result.reference_tokens.insert(result.reference_tokens.end(), lhs.reference_tokens.begin(), lhs.reference_tokens.end());
+        result.reference_tokens.insert(result.reference_tokens.end(), rhs.reference_tokens.begin(), rhs.reference_tokens.end());
+        return result;
    }

    /// @brief create a new JSON pointer by appending the unescaped token at the end of the JSON pointer
    /// @sa https://json.nlohmann.me/api/json_pointer/operator_slash/
    friend json_pointer operator/(const json_pointer& lhs, string_t token) // NOLINT(performance-unnecessary-value-param)
    {
-        return json_pointer(lhs) /= std::move(token);
+        json_pointer result;
+        result.reference_tokens.reserve(lhs.reference_tokens.size() + 1);
+        result.reference_tokens.insert(result.reference_tokens.end(), lhs.reference_tokens.begin(), lhs.reference_tokens.end());
+        result.reference_tokens.push_back(std::move(token));
+        return result;
    }

    /// @brief create a new JSON pointer by appending the array-index-token at the end of the JSON pointer
    /// @sa https://json.nlohmann.me/api/json_pointer/operator_slash/
    friend json_pointer operator/(const json_pointer& lhs, std::size_t array_idx)
    {
-        return json_pointer(lhs) /= array_idx;
+        return lhs / detail::to_string<string_t>(array_idx);
    }

    /// @brief returns the parent of this JSON pointer
@@ -155,8 +171,8 @@ class json_pointer
            return *this;
        }

-        json_pointer res = *this;
-        res.pop_back();
+        json_pointer res;
+        res.reference_tokens = std::vector<string_t>(reference_tokens.begin(), reference_tokens.end() - 1);
        return res;
    }

@@ -245,14 +261,14 @@ class json_pointer

  private:
    /// @throw out_of_range.405 always
-    JSON_HEDLEY_NO_RETURN static void throw_no_parent()
+    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE static void throw_no_parent()
    {
        JSON_THROW(detail::out_of_range::create(detail::exception_id::patch_on_root, "JSON pointer has no parent", nullptr));
    }

    /// @throw out_of_range.404 always
    template<typename BasicJsonContext>
-    JSON_HEDLEY_NO_RETURN static void throw_unresolved(const string_t& reference_token, BasicJsonContext context)
+    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE static void throw_unresolved(const string_t& reference_token, BasicJsonContext context)
    {
        static_cast<void>(reference_token); // unused when JSON_NOEXCEPTION is defined
        static_cast<void>(context);
@@ -305,6 +321,28 @@ class json_pointer
            return array_index_status::not_a_number;
        }

+        // fast path: up to 18 decimal digits cannot overflow unsigned long long or
+        // size_type (9 digits for a 32-bit size_type), so strtoull and errno are not needed
+        constexpr std::size_t max_fast_digits = sizeof(size_type) >= 8 ? 18 : 9;
+        if (!s.empty() && s.size() <= max_fast_digits)
+        {
+            size_type acc = 0;
+            for (std::size_t i = 0; i < s.size(); ++i)
+            {
+                const char c = s[i];
+                if (JSON_HEDLEY_UNLIKELY(c < '0' || c > '9'))
+                {
+                    break; // not a plain number: let strtoull decide
+                }
+                acc = static_cast<size_type>(acc * 10 + static_cast<size_type>(c - '0'));
+                if (JSON_HEDLEY_UNLIKELY(i == s.size() - 1))
+                {
+                    idx = acc;
+                    return array_index_status::ok;
+                }
+            }
+        }
+
        const char* p = s.data();
        char* p_end = nullptr; // NOLINT(misc-const-correctness)
        errno = 0; // strtoull doesn't reset errno
@@ -361,6 +399,83 @@ class json_pointer
        return idx;
    }

+    /*!
+    @brief compare with a JSON pointer string without splitting it into tokens
+
+    @throw parse_error.107  if the string is not empty or begins with '/'
+    @throw parse_error.108  if character '~' is not followed by '0' or '1'
+    */
+    bool equals_string(const string_t& reference_string) const
+    {
+        if (reference_string.empty())
+        {
+            return reference_tokens.empty();
+        }
+
+        if (JSON_HEDLEY_UNLIKELY(reference_string[0] != '/'))
+        {
+            JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_missing_slash, 1, detail::concat("JSON pointer must be empty or begin with '/' - was: '", reference_string, "'"), nullptr));
+        }
+
+        // the whole string is validated, whether or not it matches
+        const std::size_t size = reference_string.size();
+        for (std::size_t pos = reference_string.find_first_of('~');
+                pos != string_t::npos;
+                pos = reference_string.find_first_of('~', pos + 1))
+        {
+            if (JSON_HEDLEY_UNLIKELY(pos == size - 1 || (reference_string[pos + 1] != '0' && reference_string[pos + 1] != '1')))
+            {
+                JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_invalid_escape, 0, "escape character '~' must be followed with '0' or '1'", nullptr));
+            }
+        }
+
+        // compare token by token, unescaping the string on the fly
+        std::size_t pos = 0; // the slash in front of the next token
+        for (const auto& reference_token : reference_tokens)
+        {
+            if (pos >= size)
+            {
+                return false;
+            }
+
+            std::size_t i = pos + 1;
+            std::size_t j = 0;
+            const std::size_t token_size = reference_token.size();
+            while (i < size && reference_string[i] != '/')
+            {
+                char c = reference_string[i++];
+                if (c == '~')
+                {
+                    c = (reference_string[i++] == '0') ? '~' : '/';
+                }
+                if (j == token_size || reference_token[j] != c)
+                {
+                    return false;
+                }
+                ++j;
+            }
+            if (j != token_size)
+            {
+                return false;
+            }
+            pos = i;
+        }
+        return pos == size;
+    }
+
+    /// @brief object member access with a key that is only copied if it is inserted
+    template<typename BasicJsonType>
+    static BasicJsonType& object_member(BasicJsonType& object, const string_t& key)
+    {
+        auto& members = *object.m_data.m_value.object;
+        const auto it = members.find(key);
+        if (it != members.end())
+        {
+            return it->second;
+        }
+        return object.operator[](key);
+    }
+
  JSON_PRIVATE_UNLESS_TESTED:
    json_pointer top() const
    {
@@ -384,84 +499,141 @@ class json_pointer
    the result independent of the order in which the flattened object is
    iterated, which is unspecified for some object types.

-    The prefixes form a tree and are numbered, so each of them is stored only
-    once (as a node) rather than as a copy of all of its reference tokens.
+    The prefixes form a tree and are numbered (number 0 is the empty prefix),
+    so each of them is stored only once (as a node) rather than as a copy of
+    all of its reference tokens. The tree does not own the reference tokens:
+    it refers to the tokens of the parsed keys, which must outlive it.
    */
    struct prefix_tree
    {
-        // children[id] maps a reference token to the number of the prefix
-        // extended by that token; number 0 is the empty prefix
-        std::vector<std::map<string_t, std::size_t>> children;
+        // open-addressing hash table from (parent, last reference token) to
+        // the number of the node; empty slots have token == nullptr
+        struct slot
+        {
+            std::size_t hash;
+            std::size_t parent;
+            const string_t* token;
+            std::size_t id;
+
+            slot() noexcept
+                : hash(0), parent(0), token(nullptr), id(0)
+            {}
+
+            slot(std::size_t h, std::size_t p, const string_t* t, std::size_t i) noexcept
+                : hash(h), parent(p), token(t), id(i)
+            {}
+        };
+
+        std::vector<slot> slots;
+        std::size_t used = 0;
+
+        static std::size_t hash_of(std::size_t parent, const string_t& token) noexcept
+        {
+            std::size_t h = parent * static_cast<std::size_t>(0x9E3779B97F4A7C15ULL);
+            for (std::size_t i = 0; i < token.size(); ++i)
+            {
+                h = (h ^ static_cast<unsigned char>(token[i])) * static_cast<std::size_t>(0x100000001B3ULL);
+            }
+            return h ^ (h >> 29u);
+        }
+
+        void grow()
+        {
+            std::vector<slot> old(slots.size() * 2);
+            old.swap(slots);
+            const std::size_t mask = slots.size() - 1;
+            for (const auto& s : old)
+            {
+                if (s.token != nullptr)
+                {
+                    std::size_t i = s.hash & mask;
+                    while (slots[i].token != nullptr)
+                    {
+                        i = (i + 1) & mask;
+                    }
+                    slots[i] = s;
+                }
+            }
+        }
+
+        // parent[id] is the number of the prefix without its last token
+        std::vector<std::size_t> parent;
        // is_array[id] is true iff some flattened key has the reference token
        // 0 directly below the prefix with number id
        std::vector<bool> is_array;

        // start with the empty prefix only
        prefix_tree()
-            : children(1)
+            : slots(16)
+            , parent(1, 0)
            , is_array(1, false)
        {}

        // return the number of the prefix with number id extended by
        // reference_token, adding it if it is new
-        std::size_t add_child(std::size_t id, string_t&& reference_token)
+        std::size_t add_child(std::size_t id, const string_t& reference_token)
        {
+            const std::size_t hash = hash_of(id, reference_token);
+            const std::size_t mask = slots.size() - 1;
+            std::size_t i = hash & mask;
+            while (slots[i].token != nullptr)
+            {
+                if (slots[i].hash == hash && slots[i].parent == id && *slots[i].token == reference_token)
+                {
+                    return slots[i].id;
+                }
+                i = (i + 1) & mask;
+            }
+
+            // new prefix
+            const std::size_t child = parent.size();
+            slots[i] = slot(hash, id, &reference_token, child);
            if (reference_token == "0")
            {
                is_array[id] = true;
            }
+            parent.push_back(id);
+            is_array.push_back(false);

-            // read the number before the emplace_back below, which may
-            // reallocate children and invalidate the iterator
-            const std::size_t next = children.size();
-            const auto inserted = children[id].emplace(std::move(reference_token), next);
-            const std::size_t child = inserted.first->second;
-            if (inserted.second)
+            // keep the load factor below 1/2
+            if (++used * 2 > slots.size())
            {
-                children.emplace_back();
-                is_array.push_back(false);
+                grow();
            }
            return child;
        }
-
-        // return the number of the prefix with number id extended by
-        // reference_token, which must have been added before
-        std::size_t find_child(std::size_t id, const string_t& reference_token) const
-        {
-            const auto it = children[id].find(reference_token);
-            JSON_ASSERT(it != children[id].end());
-            return it->second;
-        }
    };

    /*!
    @brief create and return a reference to the pointed to value

-    Complexity: Linear in the number of reference tokens (times the logarithm
-    of the number of siblings for the prefix lookup).
+    @param[in] j  the value to create the pointed to value in
+    @param[in] tokens  the reference tokens of the pointer
+    @param[in] prefixes  prefixes[i] is the number in @a tree of the prefix
+                         consisting of the first i reference tokens
+
+    Complexity: Linear in the number of reference tokens.

    @throw parse_error.106 if an array index begins with '0'
    @throw parse_error.109 if array index is not a number
    @throw type_error.313 if value cannot be unflattened
    */
    template<typename BasicJsonType>
-    BasicJsonType& get_and_create(BasicJsonType& j, const prefix_tree& tree) const
+    static BasicJsonType& get_and_create(BasicJsonType& j, const std::vector<string_t>& tokens,
+                                         const std::vector<std::size_t>& prefixes, const prefix_tree& tree)
    {
        auto* result = &j;

-        // the number of the prefix consumed so far; used to look up whether
-        // the value to be created below is an array or an object
-        std::size_t id = 0;
-
        // in case no reference tokens exist, return a reference to the JSON value
        // j which will be overwritten by a primitive value
-        for (const auto& reference_token : reference_tokens)
+        for (std::size_t i = 0; i < tokens.size(); ++i)
        {
+            const auto& reference_token = tokens[i];
            switch (result->type())
            {
                case detail::value_t::null:
                {
-                    if (tree.is_array[id])
+                    if (tree.is_array[prefixes[i]])
                    {
                        // some reference token below this position is 0, so the
                        // value is an array
@@ -478,7 +650,7 @@ class json_pointer
                case detail::value_t::object:
                {
                    // create an entry in the object
-                    result = &result->operator[](reference_token);
+                    result = &object_member(*result, reference_token);
                    break;
                }

@@ -505,8 +677,6 @@ class json_pointer
                default:
                    JSON_THROW(detail::type_error::create(detail::exception_id::unflatten_invalid_value, "invalid value to unflatten", &j));
            }
-
-            id = tree.find_child(id, reference_token);
        }

        return *result;
@@ -558,7 +728,7 @@ class json_pointer
                case detail::value_t::object:
                {
                    // use unchecked object access
-                    ptr = &ptr->operator[](reference_token);
+                    ptr = &object_member(*ptr, reference_token);
                    break;
                }

@@ -608,8 +778,13 @@ class json_pointer
            {
                case detail::value_t::object:
                {
-                    // note: at performs range check
-                    ptr = &ptr->at(reference_token);
+                    const auto it = ptr->m_data.m_value.object->find(reference_token);
+                    if (JSON_HEDLEY_UNLIKELY(it == ptr->m_data.m_value.object->end()))
+                    {
+                        // at() throws out_of_range.403 with the usual message
+                        ptr->at(reference_token);
+                    }
+                    ptr = &it->second;
                    break;
                }

@@ -630,7 +805,7 @@ class json_pointer
                        JSON_THROW(detail::out_of_range::create(detail::exception_id::array_index_out_of_range, detail::concat(
                                "array index ", std::to_string(idx), " is out of range"), ptr));
                    }
-                    ptr = &ptr->operator[](idx);
+                    ptr = &(*ptr->m_data.m_value.array)[idx];
                    break;
                }

@@ -678,7 +853,9 @@ class json_pointer
                {
                    // use unchecked object access; the const operator[]
                    // asserts that the key exists
-                    ptr = &ptr->operator[](reference_token);
+                    const auto it = ptr->m_data.m_value.object->find(reference_token);
+                    JSON_ASSERT(it != ptr->m_data.m_value.object->end());
+                    ptr = &it->second;
                    break;
                }

@@ -692,7 +869,9 @@ class json_pointer

                    // use unchecked array access; the const operator[]
                    // asserts that the index exists
-                    ptr = &ptr->operator[](array_index<BasicJsonType>(reference_token));
+                    const auto idx = array_index<BasicJsonType>(reference_token);
+                    JSON_ASSERT(idx < ptr->m_data.m_value.array->size());
+                    ptr = &(*ptr->m_data.m_value.array)[idx];
                    break;
                }

@@ -733,12 +912,12 @@ class json_pointer
            {
                case detail::value_t::object:
                {
-                    const auto it = ptr->find(reference_token);
-                    if (JSON_HEDLEY_UNLIKELY(it == ptr->end()))
+                    const auto it = ptr->m_data.m_value.object->find(reference_token);
+                    if (JSON_HEDLEY_UNLIKELY(it == ptr->m_data.m_value.object->end()))
                    {
                        return nullptr;
                    }
-                    ptr = &*it;
+                    ptr = &it->second;
                    break;
                }

@@ -775,7 +954,7 @@ class json_pointer
                    {
                        return nullptr;
                    }
-                    ptr = &ptr->operator[](idx);
+                    ptr = &(*ptr->m_data.m_value.array)[idx];
                    break;
                }

@@ -808,13 +987,14 @@ class json_pointer
            {
                case detail::value_t::object:
                {
-                    if (!ptr->contains(reference_token))
+                    const auto it = ptr->m_data.m_value.object->find(reference_token);
+                    if (it == ptr->m_data.m_value.object->end())
                    {
                        // we did not find the key in the object
                        return false;
                    }

-                    ptr = &ptr->operator[](reference_token);
+                    ptr = &it->second;
                    break;
                }

@@ -836,13 +1016,13 @@ class json_pointer
                        return false;
                    }

-                    if (idx >= ptr->size())
+                    if (idx >= ptr->m_data.m_value.array->size())
                    {
                        // index out of range
                        return false;
                    }

-                    ptr = &ptr->operator[](idx);
+                    ptr = &(*ptr->m_data.m_value.array)[idx];
                    break;
                }

@@ -892,6 +1072,15 @@ class json_pointer
            JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_missing_slash, 1, detail::concat("JSON pointer must be empty or begin with '/' - was: '", reference_string, "'"), nullptr));
        }

+        // every slash starts a reference token
+        const std::size_t size = reference_string.size();
+        std::size_t token_count = 0;
+        for (std::size_t i = 0; i < size; ++i)
+        {
+            token_count += (reference_string[i] == '/') ? 1 : 0;
+        }
+        result.reserve(token_count);
+
        // extract the reference tokens:
        // - slash: position of the last read slash (or end of string)
        // - start: position after the previous slash
@@ -913,31 +1102,52 @@ class json_pointer
            const auto count = (slash == string_t::npos ? reference_string.size() : slash) - start;
            auto reference_token = string_t(reference_string.data() + start, count);

-            // check reference tokens are properly escaped
-            for (std::size_t pos = reference_token.find_first_of('~');
-                    pos != string_t::npos;
-                    pos = reference_token.find_first_of('~', pos + 1))
+            // check reference tokens are properly escaped; a token without
+            // a '~' (the common case) needs neither check nor unescaping
+            std::size_t pos = reference_token.find_first_of('~');
+            if (pos != string_t::npos)
            {
-                JSON_ASSERT(reference_token[pos] == '~');
-
-                // ~ must be followed by 0 or 1
-                if (JSON_HEDLEY_UNLIKELY(pos == reference_token.size() - 1 ||
-                                         (reference_token[pos + 1] != '0' &&
-                                          reference_token[pos + 1] != '1')))
+                for (; pos != string_t::npos; pos = reference_token.find_first_of('~', pos + 1))
                {
-                    JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_invalid_escape, 0, "escape character '~' must be followed with '0' or '1'", nullptr));
+                    JSON_ASSERT(reference_token[pos] == '~');
+
+                    // ~ must be followed by 0 or 1
+                    if (JSON_HEDLEY_UNLIKELY(pos == reference_token.size() - 1 ||
+                                             (reference_token[pos + 1] != '0' &&
+                                              reference_token[pos + 1] != '1')))
+                    {
+                        JSON_THROW(detail::parse_error::create(detail::exception_id::pointer_invalid_escape, 0, "escape character '~' must be followed with '0' or '1'", nullptr));
+                    }
                }
+
+                detail::unescape(reference_token);
            }

            // finally, store the reference token
-            detail::unescape(reference_token);
-            result.push_back(reference_token);
+            result.push_back(std::move(reference_token));
        }

        return result;
    }

  private:
+    // Add the entry (key, v) to the object `obj`. Flattened paths are pairwise
+    // distinct, so objects that can append a key known to be absent
+    // (ordered_map) skip the lookup, which is linear and would make flatten
+    // quadratic; all other object types use operator[].
+    template<typename ObjectType, typename ValueType>
+    static auto add_flattened(ObjectType& obj, const string_t& key, ValueType&& v, detail::priority_tag<1> /*unused*/)
+    -> decltype(obj.emplace_new_key(key, std::forward<ValueType>(v)), void())
+    {
+        obj.emplace_new_key(key, std::forward<ValueType>(v));
+    }
+
+    template<typename ObjectType, typename ValueType>
+    static void add_flattened(ObjectType& obj, const string_t& key, ValueType&& v, detail::priority_tag<0> /*unused*/)
+    {
+        obj[key] = std::forward<ValueType>(v);
+    }
+
    /*!
    @param[in] reference_string  the reference string to the current value
    @param[in] value             the value to consider
@@ -982,7 +1192,8 @@ class json_pointer

        // flatten `v`, whose path is `path`: primitives and empty containers
        // are added to the result right away; other containers get a frame
-        const auto enter = [&stack, &path, &result](const BasicJsonType & v)
+        auto& object = *result.m_data.m_value.object;
+        const auto enter = [&stack, &path, &object](const BasicJsonType & v)
        {
            switch (v.type())
            {
@@ -991,7 +1202,7 @@ class json_pointer
                    if (v.m_data.m_value.array->empty())
                    {
                        // flatten empty array as null
-                        result[path] = nullptr;
+                        add_flattened(object, path, nullptr, detail::priority_tag<1> {});
                    }
                    else
                    {
@@ -1005,7 +1216,7 @@ class json_pointer
                    if (v.m_data.m_value.object->empty())
                    {
                        // flatten empty object as null
-                        result[path] = nullptr;
+                        add_flattened(object, path, nullptr, detail::priority_tag<1> {});
                    }
                    else
                    {
@@ -1025,7 +1236,7 @@ class json_pointer
                default:
                {
                    // add a primitive value with its reference string
-                    result[path] = v;
+                    add_flattened(object, path, v, detail::priority_tag<1> {});
                    return;
                }
            }
@@ -1071,6 +1282,10 @@ class json_pointer
                enter(it->second);
            }
        }
+
+        // the entries were added without going through basic_json, so the
+        // parent pointers (JSON_DIAGNOSTICS) have to be set now
+        result.set_parents();
    }

    /*!
@@ -1094,21 +1309,53 @@ class json_pointer

        BasicJsonType result;

+        // parse every key once; the reference tokens are kept for the second
+        // pass (the vectors are never resized, so the tree may refer to them)
+        std::vector<std::vector<string_t>> keys;
+        keys.reserve(value.m_data.m_value.object->size());
+        for (const auto& element : *value.m_data.m_value.object)
+        {
+            json_pointer ptr(element.first);
+            keys.push_back(std::move(ptr.reference_tokens));
+        }
+
        // collect the pointer prefixes that have a reference token 0 among
        // their children; the values below them are arrays, all others are
        // objects (see prefix_tree)
        prefix_tree tree;
-        for (const auto& element : *value.m_data.m_value.object)
+        // the number of the prefix with i + 1 tokens of the previous key; keys
+        // are often sorted, so most of the prefix is the same as for the
+        // previous key and need not be looked up again
+        std::vector<std::size_t> path;
+        const std::vector<string_t>* previous = nullptr;
+        // the number of the complete prefix (i.e., the key) of each key
+        std::vector<std::size_t> leaves;
+        leaves.reserve(keys.size());
+        for (const auto& tokens : keys)
        {
-            json_pointer ptr(element.first);
-            std::size_t id = 0;
-            for (auto& reference_token : ptr.reference_tokens)
+            std::size_t common = 0;
+            if (previous != nullptr)
            {
-                id = tree.add_child(id, std::move(reference_token));
+                const std::size_t limit = (std::min)(tokens.size(), previous->size());
+                while (common < limit && tokens[common] == (*previous)[common])
+                {
+                    ++common;
+                }
            }
+            path.resize(common);
+            std::size_t id = common == 0 ? 0 : path[common - 1];
+            for (std::size_t i = common; i < tokens.size(); ++i)
+            {
+                id = tree.add_child(id, tokens[i]);
+                path.push_back(id);
+            }
+            leaves.push_back(id);
+            previous = &tokens;
        }

        // iterate the JSON object values
+        std::vector<std::size_t> prefixes;
+        std::size_t key_index = 0;
        for (const auto& element : *value.m_data.m_value.object)
        {
            if (JSON_HEDLEY_UNLIKELY(!element.second.is_primitive()))
@@ -1116,11 +1363,21 @@ class json_pointer
                JSON_THROW(detail::type_error::create(detail::exception_id::unflatten_value_not_primitive, "values in object must be primitive", &element.second));
            }

+            const auto& tokens = keys[key_index];
+            // number the prefixes of this key from its last one to the first
+            prefixes.resize(tokens.size());
+            for (std::size_t i = tokens.size(), id = leaves[key_index]; i > 0; --i)
+            {
+                id = tree.parent[id];
+                prefixes[i - 1] = id;
+            }
+            ++key_index;
+
            // Assign the value to the reference pointed to by JSON pointer. Note
            // that if the JSON pointer is "" (i.e., points to the whole value),
            // function get_and_create returns a reference to the result itself.
            // An assignment will then create a primitive value.
-            json_pointer(element.first).get_and_create(result, tree) = element.second;
+            get_and_create(result, tokens, prefixes, tree) = element.second;
        }

        return result;
@@ -1159,7 +1416,7 @@ class json_pointer
        = delete;
 #else
    {
-        return *this == json_pointer(rhs);
+        return equals_string(rhs);
    }
 #endif

@@ -1243,7 +1500,7 @@ inline bool operator==(const json_pointer<RefStringTypeLhs>& lhs,
    = delete;
 #else
 {
-    return lhs == json_pointer<RefStringTypeLhs>(rhs);
+    return lhs.equals_string(rhs);
 }
 #endif

@@ -1256,7 +1513,7 @@ inline bool operator==(const StringType& lhs,
    = delete;
 #else
 {
-    return json_pointer<RefStringTypeRhs>(lhs) == rhs;
+    return rhs.equals_string(lhs);
 }
 #endif

@@ -9,9 +9,11 @@
 #pragma once

 #include <limits> // numeric_limits
+#include <map> // map, multimap
 #include <string> // char_traits
 #include <tuple> // tuple
 #include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
+#include <unordered_map> // unordered_map, unordered_multimap
 #include <utility> // declval
 #include <vector> // vector
 #if defined(__cpp_lib_byte) && __cpp_lib_byte >= 201603L
@@ -683,6 +685,22 @@ struct is_compatible_integer_type
    : is_compatible_integer_type_impl<RealIntegerType,
      CompatibleNumberIntegerType> {};

+// whether to_json() stores an integer of type CompatibleNumberIntegerType as
+// number_integer
+template<typename BasicJsonType, typename CompatibleNumberIntegerType, typename = void>
+struct is_compatible_number_integer_type
+    : is_compatible_integer_type<typename BasicJsonType::number_integer_t, CompatibleNumberIntegerType> {};
+
+// if number_unsigned_t is the same type as number_integer_t, unsigned integers
+// are stored as number_integer as well (#2573)
+template<typename BasicJsonType, typename CompatibleNumberIntegerType>
+struct is_compatible_number_integer_type<BasicJsonType, CompatibleNumberIntegerType,
+           enable_if_t<conjunction<std::is_same<typename BasicJsonType::number_integer_t, typename BasicJsonType::number_unsigned_t>,
+           std::is_integral<CompatibleNumberIntegerType>,
+           std::is_unsigned<CompatibleNumberIntegerType>,
+           negation<std::is_same<bool, CompatibleNumberIntegerType>>>::value>>
+           : std::is_constructible<typename BasicJsonType::number_integer_t, CompatibleNumberIntegerType> {};
+
 template<typename BasicJsonType, typename CompatibleType, typename = void>
 struct is_compatible_type_impl: std::false_type {};

@@ -897,6 +915,31 @@ struct has_capacity : std::integral_constant<bool, is_detected<detect_capacity,
 template <typename T>
 struct is_ordered_map : has_capacity<T> {};

+// whether T is a specialization of nlohmann::ordered_map, which only ever
+// appends members, so they can only move when its capacity changes
+template<typename T>
+struct is_nlohmann_ordered_map : std::false_type {};
+
+template<class Key, class T, class IgnoredLess, class Allocator>
+struct is_nlohmann_ordered_map<ordered_map<Key, T, IgnoredLess, Allocator>> : std::true_type {};
+
+// whether adding or erasing elements never moves the other elements of the
+// container T; only node-based standard containers are known to guarantee this
+template<typename T>
+struct has_stable_elements : std::false_type {};
+
+template<class Key, class T, class Compare, class Allocator>
+struct has_stable_elements<std::map<Key, T, Compare, Allocator>> : std::true_type {};
+
+template<class Key, class T, class Compare, class Allocator>
+struct has_stable_elements<std::multimap<Key, T, Compare, Allocator>> : std::true_type {};
+
+template<class Key, class T, class Hash, class KeyEqual, class Allocator>
+struct has_stable_elements<std::unordered_map<Key, T, Hash, KeyEqual, Allocator>> : std::true_type {};
+
+template<class Key, class T, class Hash, class KeyEqual, class Allocator>
+struct has_stable_elements<std::unordered_multimap<Key, T, Hash, KeyEqual, Allocator>> : std::true_type {};
+
 // to avoid useless casts (see https://github.com/nlohmann/json/issues/2893#issuecomment-889152324)
 template < typename T, typename U, enable_if_t < !std::is_same<T, U>::value, int > = 0 >
 T conditional_static_cast(U value)
@@ -1020,6 +1063,25 @@ constexpr bool value_in_range_of(T val)
 template<bool Value>
 using bool_constant = std::integral_constant<bool, Value>;

+// Stands in for number_unsigned_t in overload sets if it is the same type as
+// number_integer_t, so that the unsigned overloads do not collide with the
+// integer ones. Never constructed. Such a basic_json stores every integer as
+// number_integer (#2573).
+struct same_as_number_integer_type {};
+
+// NumberUnsignedType, or same_as_number_integer_type if it is the same type as
+// NumberIntegerType; basic_json uses this one, as it cannot name its own member
+// types through an incomplete basic_json (MSVC reports a recursive alias, and
+// old GCC versions crash)
+template<typename NumberIntegerType, typename NumberUnsignedType>
+using number_unsigned_overload_type = typename std::conditional<std::is_same<NumberIntegerType, NumberUnsignedType>::value,
+      same_as_number_integer_type, NumberUnsignedType>::type;
+
+// number_unsigned_t of BasicJsonType, or same_as_number_integer_type if it is
+// the same type as number_integer_t
+template<typename BasicJsonType>
+using number_unsigned_overload_t = number_unsigned_overload_type<typename BasicJsonType::number_integer_t, typename BasicJsonType::number_unsigned_t>;
+
 ///////////////////////////////////////////////////////////////////////////////
 // is_c_string
 ///////////////////////////////////////////////////////////////////////////////
@@ -221,7 +221,7 @@ class binary_writer

            case value_t::number_unsigned:
            {
-                write_cbor_head(0x00, j.m_data.m_value.number_unsigned);
+                write_cbor_head(0x00, conditional_static_cast<std::uint64_t>(j.m_data.m_value.number_unsigned));
                break;
            }

@@ -1601,7 +1601,7 @@ class binary_writer
                return calc_bson_integer_size(j.m_data.m_value.number_integer);

            case value_t::number_unsigned:
-                return calc_bson_unsigned_size(j.m_data.m_value.number_unsigned);
+                return calc_bson_unsigned_size(conditional_static_cast<std::uint64_t>(j.m_data.m_value.number_unsigned));

            case value_t::string:
                return calc_bson_string_size(*j.m_data.m_value.string, j);
@@ -1643,7 +1643,7 @@ class binary_writer
                return write_bson_integer(name, j.m_data.m_value.number_integer);

            case value_t::number_unsigned:
-                return write_bson_unsigned(name, j.m_data.m_value.number_unsigned);
+                return write_bson_unsigned(name, conditional_static_cast<std::uint64_t>(j.m_data.m_value.number_unsigned));

            case value_t::string:
                return write_bson_string(name, *j.m_data.m_value.string);
@@ -49,6 +49,12 @@ class serializer
    using number_float_t = typename BasicJsonType::number_float_t;
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
+    /// type of the absolute value of an integer: number_unsigned_t, or its
+    /// unsigned counterpart if it is signed (it may be number_integer_t, #2573)
+    using number_magnitude_t = typename std::conditional <
+                               std::is_integral<number_unsigned_t>::value && std::is_signed<number_unsigned_t>::value,
+                               std::make_unsigned<number_unsigned_t>,
+                               std::enable_if<true, number_unsigned_t >>::type::type;
    using binary_char_t = typename BasicJsonType::binary_t::value_type;

  public:
@@ -772,6 +778,33 @@ class serializer
                        break;
                    }
                }
+
+                // A byte below 0x60 is a complete code point and needs no
+                // UTF-8 decoding. The scanner stops only at a control
+                // character, a quote, or a backslash in that range, so look up
+                // its escape sequence and write all 8 bytes of the table entry
+                // straight into the write buffer; only the length stored in the
+                // last byte of the entry is kept.
+                if (data[i] < 0x60)
+                {
+                    // emit any bytes still pending in string_buffer first to
+                    // preserve output order
+                    if (bytes != 0)
+                    {
+                        put_buffer(string_buffer, bytes);
+                        bytes = 0;
+                    }
+                    const auto& escape = ascii_escapes()[data[i]];
+                    if (JSON_HEDLEY_UNLIKELY(write_buffer.size() - write_buffer_pos < escape.size()))
+                    {
+                        flush();
+                    }
+                    std::memcpy(write_buffer.data() + write_buffer_pos, escape.data(), escape.size());
+                    write_buffer_pos += static_cast<std::size_t>(escape[7]);
+                    bytes_after_last_accept = 0;
+                    undumped_chars = 0;
+                    continue;
+                }
            }

            const auto byte = static_cast<std::uint8_t>(s[i]);
@@ -780,92 +813,39 @@ class serializer
            {
                case UTF8_ACCEPT:  // decode found a new code point
                {
-                    switch (codepoint)
+                    // the code point is at least 0x60 (smaller ones are handled
+                    // above) and is not printable ASCII (which the scanner
+                    // copies): it is DEL (0x7F) under EnsureAscii or a non-ASCII
+                    // character
+                    if (EnsureAscii)
                    {
-                        case 0x08: // backspace
+                        JSON_ASSERT(codepoint >= 0x7F);
+                        if (error_handler == error_handler_t::keep)
                        {
-                            string_buffer[bytes++] = '\\';
-                            string_buffer[bytes++] = 'b';
-                            break;
+                            // this character was buffered as raw bytes below
+                            // in case it turned out to be part of an
+                            // ill-formed sequence (which is kept as is); now
+                            // that it decoded to a well-formed code point,
+                            // undo that and \u-escape it like any other
+                            // character instead
+                            bytes = bytes_after_last_accept;
                        }
-
-                        case 0x09: // horizontal tab
+                        if (codepoint <= 0xFFFF)
                        {
-                            string_buffer[bytes++] = '\\';
-                            string_buffer[bytes++] = 't';
-                            break;
+                            write_u_escape(bytes, static_cast<std::uint16_t>(codepoint));
                        }
-
-                        case 0x0A: // newline
+                        else
                        {
-                            string_buffer[bytes++] = '\\';
-                            string_buffer[bytes++] = 'n';
-                            break;
-                        }
-
-                        case 0x0C: // formfeed
-                        {
-                            string_buffer[bytes++] = '\\';
-                            string_buffer[bytes++] = 'f';
-                            break;
-                        }
-
-                        case 0x0D: // carriage return
-                        {
-                            string_buffer[bytes++] = '\\';
-                            string_buffer[bytes++] = 'r';
-                            break;
-                        }
-
-                        case 0x22: // quotation mark
-                        {
-                            string_buffer[bytes++] = '\\';
-                            string_buffer[bytes++] = '"';
-                            break;
-                        }
-
-                        case 0x5C: // reverse solidus
-                        {
-                            string_buffer[bytes++] = '\\';
-                            string_buffer[bytes++] = '\\';
-                            break;
-                        }
-
-                        default:
-                        {
-                            // escape control characters (0x00..0x1F) or, if
-                            // EnsureAscii parameter is used, non-ASCII characters
-                            if ((codepoint <= 0x1F) || (EnsureAscii && (codepoint >= 0x7F)))
-                            {
-                                if (EnsureAscii && error_handler == error_handler_t::keep)
-                                {
-                                    // this character was buffered as raw bytes
-                                    // below in case it turned out to be part of
-                                    // an ill-formed sequence (which is kept as
-                                    // is); now that it decoded to a well-formed
-                                    // code point, undo that and \u-escape it
-                                    // like any other character instead
-                                    bytes = bytes_after_last_accept;
-                                }
-                                if (codepoint <= 0xFFFF)
-                                {
-                                    write_u_escape(bytes, static_cast<std::uint16_t>(codepoint));
-                                }
-                                else
-                                {
-                                    write_u_escape(bytes, static_cast<std::uint16_t>(0xD7C0u + (codepoint >> 10u)));
-                                    write_u_escape(bytes, static_cast<std::uint16_t>(0xDC00u + (codepoint & 0x3FFu)));
-                                }
-                            }
-                            else
-                            {
-                                // copy byte to buffer (all previous bytes
-                                // been copied have in default case above)
-                                string_buffer[bytes++] = s[i];
-                            }
-                            break;
+                            write_u_escape(bytes, static_cast<std::uint16_t>(0xD7C0u + (codepoint >> 10u)));
+                            write_u_escape(bytes, static_cast<std::uint16_t>(0xDC00u + (codepoint & 0x3FFu)));
                        }
                    }
+                    else
+                    {
+                        // copy byte to buffer (all previous bytes of the
+                        // sequence have been copied in the default case below)
+                        string_buffer[bytes++] = s[i];
+                    }

                    // write buffer and reset index; there must be 13 bytes
                    // left, as this is the maximal number of bytes to be
@@ -1227,7 +1207,7 @@ class serializer
    @param[in] x  unsigned integer number to count its digits
    @return    number of decimal digits
    */
-    unsigned int count_digits(number_unsigned_t x) noexcept
+    unsigned int count_digits(number_magnitude_t x) noexcept
    {
        unsigned int n_digits = 1;
        for (;;)
@@ -1253,6 +1233,121 @@ class serializer
        }
    }

+    /*!
+    @brief the JSON form of each character below 0x60
+
+    Entry c holds the escape sequence of character c - the short form for
+    \\b, \\t, \\n, \\f, \\r, \\" and \\\\, \\u00xx for the other control characters -
+    or c itself if it needs no escaping, padded with zeros to 7 bytes. The last
+    byte is the length of the sequence. The 8 bytes of an entry are copied at
+    once, so writing an escape needs neither a branch nor a byte-wise loop.
+    */
+    static const std::array<std::array<char, 8>, 0x60>& ascii_escapes() noexcept
+    {
+        static const std::array<std::array<char, 8>, 0x60> escapes =
+        {
+            {
+                {{'\\', 'u', '0', '0', '0', '0', 0, 6}}, // 0x00
+                {{'\\', 'u', '0', '0', '0', '1', 0, 6}}, // 0x01
+                {{'\\', 'u', '0', '0', '0', '2', 0, 6}}, // 0x02
+                {{'\\', 'u', '0', '0', '0', '3', 0, 6}}, // 0x03
+                {{'\\', 'u', '0', '0', '0', '4', 0, 6}}, // 0x04
+                {{'\\', 'u', '0', '0', '0', '5', 0, 6}}, // 0x05
+                {{'\\', 'u', '0', '0', '0', '6', 0, 6}}, // 0x06
+                {{'\\', 'u', '0', '0', '0', '7', 0, 6}}, // 0x07
+                {{'\\', 'b', 0, 0, 0, 0, 0, 2}}, // 0x08
+                {{'\\', 't', 0, 0, 0, 0, 0, 2}}, // 0x09
+                {{'\\', 'n', 0, 0, 0, 0, 0, 2}}, // 0x0A
+                {{'\\', 'u', '0', '0', '0', 'b', 0, 6}}, // 0x0B
+                {{'\\', 'f', 0, 0, 0, 0, 0, 2}}, // 0x0C
+                {{'\\', 'r', 0, 0, 0, 0, 0, 2}}, // 0x0D
+                {{'\\', 'u', '0', '0', '0', 'e', 0, 6}}, // 0x0E
+                {{'\\', 'u', '0', '0', '0', 'f', 0, 6}}, // 0x0F
+                {{'\\', 'u', '0', '0', '1', '0', 0, 6}}, // 0x10
+                {{'\\', 'u', '0', '0', '1', '1', 0, 6}}, // 0x11
+                {{'\\', 'u', '0', '0', '1', '2', 0, 6}}, // 0x12
+                {{'\\', 'u', '0', '0', '1', '3', 0, 6}}, // 0x13
+                {{'\\', 'u', '0', '0', '1', '4', 0, 6}}, // 0x14
+                {{'\\', 'u', '0', '0', '1', '5', 0, 6}}, // 0x15
+                {{'\\', 'u', '0', '0', '1', '6', 0, 6}}, // 0x16
+                {{'\\', 'u', '0', '0', '1', '7', 0, 6}}, // 0x17
+                {{'\\', 'u', '0', '0', '1', '8', 0, 6}}, // 0x18
+                {{'\\', 'u', '0', '0', '1', '9', 0, 6}}, // 0x19
+                {{'\\', 'u', '0', '0', '1', 'a', 0, 6}}, // 0x1A
+                {{'\\', 'u', '0', '0', '1', 'b', 0, 6}}, // 0x1B
+                {{'\\', 'u', '0', '0', '1', 'c', 0, 6}}, // 0x1C
+                {{'\\', 'u', '0', '0', '1', 'd', 0, 6}}, // 0x1D
+                {{'\\', 'u', '0', '0', '1', 'e', 0, 6}}, // 0x1E
+                {{'\\', 'u', '0', '0', '1', 'f', 0, 6}}, // 0x1F
+                {{' ', 0, 0, 0, 0, 0, 0, 1}}, // 0x20
+                {{'!', 0, 0, 0, 0, 0, 0, 1}}, // 0x21
+                {{'\\', '"', 0, 0, 0, 0, 0, 2}}, // 0x22
+                {{'#', 0, 0, 0, 0, 0, 0, 1}}, // 0x23
+                {{'$', 0, 0, 0, 0, 0, 0, 1}}, // 0x24
+                {{'%', 0, 0, 0, 0, 0, 0, 1}}, // 0x25
+                {{'&', 0, 0, 0, 0, 0, 0, 1}}, // 0x26
+                {{'\'', 0, 0, 0, 0, 0, 0, 1}}, // 0x27
+                {{'(', 0, 0, 0, 0, 0, 0, 1}}, // 0x28
+                {{')', 0, 0, 0, 0, 0, 0, 1}}, // 0x29
+                {{'*', 0, 0, 0, 0, 0, 0, 1}}, // 0x2A
+                {{'+', 0, 0, 0, 0, 0, 0, 1}}, // 0x2B
+                {{',', 0, 0, 0, 0, 0, 0, 1}}, // 0x2C
+                {{'-', 0, 0, 0, 0, 0, 0, 1}}, // 0x2D
+                {{'.', 0, 0, 0, 0, 0, 0, 1}}, // 0x2E
+                {{'/', 0, 0, 0, 0, 0, 0, 1}}, // 0x2F
+                {{'0', 0, 0, 0, 0, 0, 0, 1}}, // 0x30
+                {{'1', 0, 0, 0, 0, 0, 0, 1}}, // 0x31
+                {{'2', 0, 0, 0, 0, 0, 0, 1}}, // 0x32
+                {{'3', 0, 0, 0, 0, 0, 0, 1}}, // 0x33
+                {{'4', 0, 0, 0, 0, 0, 0, 1}}, // 0x34
+                {{'5', 0, 0, 0, 0, 0, 0, 1}}, // 0x35
+                {{'6', 0, 0, 0, 0, 0, 0, 1}}, // 0x36
+                {{'7', 0, 0, 0, 0, 0, 0, 1}}, // 0x37
+                {{'8', 0, 0, 0, 0, 0, 0, 1}}, // 0x38
+                {{'9', 0, 0, 0, 0, 0, 0, 1}}, // 0x39
+                {{':', 0, 0, 0, 0, 0, 0, 1}}, // 0x3A
+                {{';', 0, 0, 0, 0, 0, 0, 1}}, // 0x3B
+                {{'<', 0, 0, 0, 0, 0, 0, 1}}, // 0x3C
+                {{'=', 0, 0, 0, 0, 0, 0, 1}}, // 0x3D
+                {{'>', 0, 0, 0, 0, 0, 0, 1}}, // 0x3E
+                {{'?', 0, 0, 0, 0, 0, 0, 1}}, // 0x3F
+                {{'@', 0, 0, 0, 0, 0, 0, 1}}, // 0x40
+                {{'A', 0, 0, 0, 0, 0, 0, 1}}, // 0x41
+                {{'B', 0, 0, 0, 0, 0, 0, 1}}, // 0x42
+                {{'C', 0, 0, 0, 0, 0, 0, 1}}, // 0x43
+                {{'D', 0, 0, 0, 0, 0, 0, 1}}, // 0x44
+                {{'E', 0, 0, 0, 0, 0, 0, 1}}, // 0x45
+                {{'F', 0, 0, 0, 0, 0, 0, 1}}, // 0x46
+                {{'G', 0, 0, 0, 0, 0, 0, 1}}, // 0x47
+                {{'H', 0, 0, 0, 0, 0, 0, 1}}, // 0x48
+                {{'I', 0, 0, 0, 0, 0, 0, 1}}, // 0x49
+                {{'J', 0, 0, 0, 0, 0, 0, 1}}, // 0x4A
+                {{'K', 0, 0, 0, 0, 0, 0, 1}}, // 0x4B
+                {{'L', 0, 0, 0, 0, 0, 0, 1}}, // 0x4C
+                {{'M', 0, 0, 0, 0, 0, 0, 1}}, // 0x4D
+                {{'N', 0, 0, 0, 0, 0, 0, 1}}, // 0x4E
+                {{'O', 0, 0, 0, 0, 0, 0, 1}}, // 0x4F
+                {{'P', 0, 0, 0, 0, 0, 0, 1}}, // 0x50
+                {{'Q', 0, 0, 0, 0, 0, 0, 1}}, // 0x51
+                {{'R', 0, 0, 0, 0, 0, 0, 1}}, // 0x52
+                {{'S', 0, 0, 0, 0, 0, 0, 1}}, // 0x53
+                {{'T', 0, 0, 0, 0, 0, 0, 1}}, // 0x54
+                {{'U', 0, 0, 0, 0, 0, 0, 1}}, // 0x55
+                {{'V', 0, 0, 0, 0, 0, 0, 1}}, // 0x56
+                {{'W', 0, 0, 0, 0, 0, 0, 1}}, // 0x57
+                {{'X', 0, 0, 0, 0, 0, 0, 1}}, // 0x58
+                {{'Y', 0, 0, 0, 0, 0, 0, 1}}, // 0x59
+                {{'Z', 0, 0, 0, 0, 0, 0, 1}}, // 0x5A
+                {{'[', 0, 0, 0, 0, 0, 0, 1}}, // 0x5B
+                {{'\\', '\\', 0, 0, 0, 0, 0, 2}}, // 0x5C
+                {{']', 0, 0, 0, 0, 0, 0, 1}}, // 0x5D
+                {{'^', 0, 0, 0, 0, 0, 0, 1}}, // 0x5E
+                {{'_', 0, 0, 0, 0, 0, 0, 1}}, // 0x5F
+            }
+        };
+        return escapes;
+    }
+
    /*!
     * @brief write a lowercase "\\uXXXX" escape sequence into @a string_buffer
     *
@@ -1410,7 +1505,7 @@ class serializer
        }
        auto* buffer_ptr = write_buffer.data() + write_buffer_pos;

-        number_unsigned_t abs_value;
+        number_magnitude_t abs_value;

        // one byte for the minus sign
        unsigned int n_chars = 0;
@@ -1423,7 +1518,7 @@ class serializer
        }
        else
        {
-            abs_value = static_cast<number_unsigned_t>(x);
+            abs_value = static_cast<number_magnitude_t>(x);
        }

        // up to 16 digits: eight at a time (as the digits of floats), written
@@ -1591,17 +1686,6 @@ class serializer
        }
    }

-    /*
-     * Overload to make the compiler happy while it is instantiating
-     * dump_integer for number_unsigned_t.
-     * Must never be called.
-     */
-    number_unsigned_t remove_sign(number_unsigned_t x)
-    {
-        JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
-        return x; // LCOV_EXCL_LINE
-    }
-
    /*
     * Helper function for dump_integer
     *
@@ -1611,10 +1695,10 @@ class serializer
     * absolute values of INT_MIN and INT_MAX are usually not the same. See
     * #1708 for details.
     */
-    number_unsigned_t remove_sign(number_integer_t x) noexcept
+    number_magnitude_t remove_sign(number_integer_t x) noexcept
    {
        JSON_ASSERT(x < 0);
-        return static_cast<number_unsigned_t>(-(x + 1)) + 1;
+        return static_cast<number_magnitude_t>(-(x + 1)) + 1;
    }

  private:
@@ -9,6 +9,7 @@
 #pragma once

 #include <cstddef> // size_t
+#include <utility> // move

 #include <nlohmann/detail/abi_macros.hpp>

@@ -24,39 +25,46 @@ namespace detail
 * Note the order of escaping "~" to "~0" and "/" to "~1" is important.
 *
 * The string is rebuilt in a single pass, appending whole runs between the
- * characters that need escaping. Scanning with find_first_of() keeps the
- * common case -- nothing to escape -- as fast as a single search, while
- * repeated replace() calls would move the tail of the string once per
- * escaped character.
+ * characters that need escaping, while repeated replace() calls would move
+ * the tail of the string once per escaped character. @ref escape_into appends
+ * the escaped string to an existing one.
 */
+template<typename StringType>
+inline void escape_into(StringType& out, const StringType& s)
+{
+    const std::size_t size = s.size();
+    std::size_t run = 0;
+    for (std::size_t i = 0; i < size; ++i)
+    {
+        const char c = s[i];
+        if (c == '~' || c == '/')
+        {
+            out.append(s.data() + run, i - run);
+            out.append(c == '~' ? "~0" : "~1", 2);
+            run = i + 1;
+        }
+    }
+    out.append(s.data() + run, size - run);
+}
+
 template<typename StringType>
 inline StringType escape(const StringType& s)
 {
-    auto next_special = [&s](std::size_t from)
+    // a single scan for both special characters; nothing to escape is the common case
+    const std::size_t size = s.size();
+    std::size_t i = 0;
+    while (i < size && s[i] != '~' && s[i] != '/')
    {
-        const auto tilde = s.find_first_of('~', from);
-        const auto slash = s.find_first_of('/', from);
-        return tilde < slash ? tilde : slash; // npos is the largest value
-    };
-
-    auto pos = next_special(0);
-    if (pos == StringType::npos)
+        ++i;
+    }
+    if (i == size)
    {
        return s;
    }

    StringType result;
-    result.reserve(s.size() + 2);
-
-    std::size_t run = 0;
-    while (pos != StringType::npos)
-    {
-        result.append(s.data() + run, pos - run);
-        result.append(s[pos] == '~' ? "~0" : "~1", 2);
-        run = pos + 1;
-        pos = next_special(run);
-    }
-    result.append(s.data() + run, s.size() - run);
+    result.reserve(size + 2);
+    escape_into(result, s);
    return result;
 }

@@ -101,7 +109,7 @@ inline void unescape(StringType& s)
        pos = s.find_first_of('~', run);
    }
    result.append(s.data() + run, s.size() - run);
-    s = result;
+    s = std::move(result);
 }

 }  // namespace detail
@@ -117,6 +117,34 @@ inline bool operator<(const value_t lhs, const value_t rhs) noexcept
 }
 #endif

+/*!
+@brief whether a value of the given type owns heap memory
+
+Strings, binaries, objects, and arrays are stored as pointers to allocated
+values; all other types are stored directly in the union. Every enumerator is
+listed so that -Wswitch-enum flags this function when a new type is added.
+*/
+inline bool owns_memory(const value_t t) noexcept
+{
+    switch (t)
+    {
+        case value_t::object:
+        case value_t::array:
+        case value_t::string:
+        case value_t::binary:
+            return true;
+
+        case value_t::null:
+        case value_t::boolean:
+        case value_t::number_integer:
+        case value_t::number_unsigned:
+        case value_t::number_float:
+        case value_t::discarded:
+        default:
+            return false;
+    }
+}
+

 /*!
@brief compare an integer with a floating point number without precision loss
@@ -90,6 +90,15 @@ private:
        return self.end();
    }

+    /// @brief throw the exception of a failed at() lookup
+    /// @note kept out of line so that at_impl() stays small enough to inline
+    /// @throw std::out_of_range always
+    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE
+    static void throw_key_not_found()
+    {
+        JSON_THROW(std::out_of_range("key not found"));
+    }
+
    /// @brief shared implementation of the const and non-const at() overloads
    /// @throw std::out_of_range if @a key is not found
    template<typename Self, typename KeyType>
@@ -98,7 +107,7 @@ private:
        const auto it = find_impl(self, key);
        if (it == self.end())
        {
-            JSON_THROW(std::out_of_range("key not found"));
+            throw_key_not_found();
        }
        return it->second;
    }
@@ -143,6 +152,17 @@ public:
        return {std::prev(this->end()), true};
    }

+    /// @brief add an element at the end without checking whether the key exists
+    /// @note The caller must guarantee that @a key is not yet contained, otherwise
+    ///       the container holds duplicate keys. This avoids the linear search of
+    ///       emplace() and operator[] when many keys known to be new are added.
+    template<class V, detail::enable_if_t<
+                 detail::is_constructible<T, V>::value, int> = 0>
+    void emplace_new_key(const key_type& key, V && t)
+    {
+        append(key, std::forward<V>(t));
+    }
+
    T& operator[](const key_type& key)
    {
        return emplace(key, T{}).first->second;
@@ -9,7 +9,10 @@
 #include <benchmark/benchmark.h>
 #include <nlohmann/json.hpp>
 #include <fstream>
+#include <array>
+#include <deque>
 #include <numeric>
+#include <set>
 #include <vector>
 #include <test_data.hpp>

@@ -621,4 +624,27 @@ static void FromCborChunkedString(benchmark::State& state, const std::size_t chu

 BENCHMARK_CAPTURE(FromCborChunkedString, 10000 chunks, 10000);

+// conversion of a JSON array into standard containers
+template<typename Container>
+static void GetArray(benchmark::State& state)
+{
+    json j = json::array();
+    for (int i = 0; i < 1000; ++i)
+    {
+        j.push_back(i);
+    }
+
+    for (auto _ : state)
+    {
+        auto c = j.get<Container>();
+        benchmark::DoNotOptimize(c);
+    }
+    state.SetItemsProcessed(state.iterations() * 1000);
+}
+
+BENCHMARK_TEMPLATE(GetArray, std::vector<int>);
+BENCHMARK_TEMPLATE(GetArray, std::deque<int>);
+BENCHMARK_TEMPLATE(GetArray, std::set<int>);
+BENCHMARK_TEMPLATE(GetArray, std::array<int, 1000>);
+
 BENCHMARK_MAIN();
@@ -9,7 +9,16 @@ Each fuzzer driver (`tests/src/fuzzer-parse_*.cpp`) parses its input twice: once
 once with exceptions. Both calls must agree. Where parsing with exceptions fails, the call without exceptions must
 return a discarded value (or throw the same kind of non-parse error), and it must never throw a `parse_error`. Where
 parsing succeeds, both calls must return the same value. The drivers then serialize the value, parse the result back,
-and check that nothing was lost. The drivers check all of this with `assert`, so they refuse to build with `NDEBUG`.
+and check that nothing was lost.
+
+Finally, each driver reads the same input through the other input adapters: a `std::istringstream`, a non-contiguous
+iterator range (`std::list<std::uint8_t>`), and, on POSIX systems, a `FILE*` from `fmemopen`. The pointer range takes the
+fast paths for contiguous input (bulk string scanning, multi-byte loads, lazy position tracking), while the other
+adapters read byte by byte. Every adapter must give the same value, or the same exception with the same id, message,
+and byte position. The JSON driver checks this for `parse` and `accept`, each with and without `ignore_comments`. The
+shared code is `check_input_adapters()` in `tests/src/fuzzer_common.hpp`.
+
+The drivers check all of this with `assert`, so they refuse to build with `NDEBUG`.

 ## Corpus creation

@@ -47,12 +47,30 @@ dumps is stable under exactly the same values that break operator==.
 The unit tests run the same checks on a fixed corpus (see the "BJData round-trip
 invariants" test case), so keep both in sync.

+Finally, it reads the data from a stream, a non-contiguous iterator range, and
+a FILE*, which read byte by byte, and checks that each gives the same value or
+error (id, message, byte position) as the pointer range, which takes the bulk
+fast paths (see check_input_adapters()).
+
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */

 #include "fuzzer_common.hpp"

+namespace
+{
+// json::from_bjdata for check_input_adapters()
+struct read_bjdata
+{
+    template<typename... Args>
+    json operator()(Args&& ... args) const
+    {
+        return json::from_bjdata(std::forward<Args>(args)...);
+    }
+};
+} // namespace
+
 // value-stable comparison for the round-trip checks below; see the note
 // above on why this compares dump()s rather than the json values directly
 static bool is_value_stable(const json& lhs, const json& rhs)
@@ -126,6 +144,9 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
    }

+    // step 3: the other input adapters must read the data alike
+    check_input_adapters(data, size, read_bjdata());
+
    // return 0 - non-zero return values are reserved for future use
    return 0;
 }
@@ -17,44 +17,33 @@ array data, it performs the following steps:
 - j2 = from_bon8(vec)
 - assert(to_bon8(j2) == vec)

-It also checks that reading the data from a stream, which reads strings byte by
-byte, gives the same value or error as reading it from contiguous memory, which
-copies strings in bulk.
+Finally, it reads the data from a stream, a non-contiguous iterator range, and
+a FILE*, which read byte by byte, and checks that each gives the same value or
+error (id, message, byte position) as the pointer range, which takes the bulk
+fast paths (see check_input_adapters()).

 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */

-#include <sstream>
 #include "fuzzer_common.hpp"

 namespace
 {
-// the serialization of the value read from @a input, or the error message
-template<typename InputType>
-std::string read_bon8(InputType&& input)
+// json::from_bon8 for check_input_adapters()
+struct read_bon8
 {
-    try
+    template<typename... Args>
+    json operator()(Args&& ... args) const
    {
-        const auto vec = json::to_bon8(json::from_bon8(std::forward<InputType>(input)));
-        return {vec.begin(), vec.end()};
+        return json::from_bon8(std::forward<Args>(args)...);
    }
-    catch (const json::exception& e)
-    {
-        return e.what();
-    }
-}
+};
 } // namespace

 // see http://llvm.org/docs/LibFuzzer.html
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
-    // contiguous and stream input must be read alike
-    {
-        std::istringstream stream(std::string(reinterpret_cast<const char*>(data), size));
-        assert(read_bon8(std::vector<uint8_t>(data, data + size)) == read_bon8(stream));
-    }
-
    std::vector<uint8_t> const vec1(data, data + size);

    // step 0: parse input without exceptions
@@ -106,6 +95,9 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
    }

+    // step 3: the other input adapters must read the data alike
+    check_input_adapters(data, size, read_bon8());
+
    // return 0 - non-zero return values are reserved for future use
    return 0;
 }
@@ -17,12 +17,30 @@ array data, it performs the following steps:
 - j2 = from_bson(vec)
 - assert(to_bson(j2) == vec)

+Finally, it reads the data from a stream, a non-contiguous iterator range, and
+a FILE*, which read byte by byte, and checks that each gives the same value or
+error (id, message, byte position) as the pointer range, which takes the bulk
+fast paths (see check_input_adapters()).
+
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */

 #include "fuzzer_common.hpp"

+namespace
+{
+// json::from_bson for check_input_adapters()
+struct read_bson
+{
+    template<typename... Args>
+    json operator()(Args&& ... args) const
+    {
+        return json::from_bson(std::forward<Args>(args)...);
+    }
+};
+} // namespace
+
 // see http://llvm.org/docs/LibFuzzer.html
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
@@ -77,6 +95,9 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
    }

+    // step 3: the other input adapters must read the data alike
+    check_input_adapters(data, size, read_bson());
+
    // return 0 - non-zero return values are reserved for future use
    return 0;
 }
@@ -17,12 +17,30 @@ array data, it performs the following steps:
 - j2 = from_cbor(vec)
 - assert(to_cbor(j2) == vec)

+Finally, it reads the data from a stream, a non-contiguous iterator range, and
+a FILE*, which read byte by byte, and checks that each gives the same value or
+error (id, message, byte position) as the pointer range, which takes the bulk
+fast paths (see check_input_adapters()).
+
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */

 #include "fuzzer_common.hpp"

+namespace
+{
+// json::from_cbor for check_input_adapters()
+struct read_cbor
+{
+    template<typename... Args>
+    json operator()(Args&& ... args) const
+    {
+        return json::from_cbor(std::forward<Args>(args)...);
+    }
+};
+} // namespace
+
 // see http://llvm.org/docs/LibFuzzer.html
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
@@ -77,6 +95,9 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
    }

+    // step 3: the other input adapters must read the data alike
+    check_input_adapters(data, size, read_cbor());
+
    // return 0 - non-zero return values are reserved for future use
    return 0;
 }
@@ -17,6 +17,12 @@ array data, it performs the following steps:
 - j2 = parse(s1)
 - s2 = serialize(j2)
 - assert(s1 == s2)
+- for ignore_comments = false and true: assert(parse(data) and accept(data)
+  give the same result for a stream, a non-contiguous iterator range, and a
+  FILE* as for the pointer range)
+
+The pointer range takes the bulk fast paths, the other input adapters read byte
+by byte; see check_input_adapters().

 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
@@ -24,6 +30,32 @@ drivers.

 #include "fuzzer_common.hpp"

+namespace
+{
+// json::parse and json::accept for check_input_adapters()
+struct parse_json
+{
+    bool ignore_comments;
+
+    template<typename... Args>
+    json operator()(Args&& ... args) const
+    {
+        return json::parse(std::forward<Args>(args)..., nullptr, true, ignore_comments);
+    }
+};
+
+struct accept_json
+{
+    bool ignore_comments;
+
+    template<typename... Args>
+    bool operator()(Args&& ... args) const
+    {
+        return json::accept(std::forward<Args>(args)..., ignore_comments);
+    }
+};
+} // namespace
+
 // see http://llvm.org/docs/LibFuzzer.html
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
@@ -76,6 +108,16 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
    }

+    // step 3: the other input adapters must read the data alike
+    for (const bool ignore_comments :
+            {
+                false, true
+            })
+    {
+        check_input_adapters(data, size, parse_json{ignore_comments});
+        check_input_adapters(data, size, accept_json{ignore_comments});
+    }
+
    // return 0 - non-zero return values are reserved for future use
    return 0;
 }
@@ -17,12 +17,30 @@ array data, it performs the following steps:
 - j2 = from_msgpack(vec)
 - assert(to_msgpack(j2) == vec)

+Finally, it reads the data from a stream, a non-contiguous iterator range, and
+a FILE*, which read byte by byte, and checks that each gives the same value or
+error (id, message, byte position) as the pointer range, which takes the bulk
+fast paths (see check_input_adapters()).
+
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */

 #include "fuzzer_common.hpp"

+namespace
+{
+// json::from_msgpack for check_input_adapters()
+struct read_msgpack
+{
+    template<typename... Args>
+    json operator()(Args&& ... args) const
+    {
+        return json::from_msgpack(std::forward<Args>(args)...);
+    }
+};
+} // namespace
+
 // see http://llvm.org/docs/LibFuzzer.html
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
@@ -77,6 +95,9 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
    }

+    // step 3: the other input adapters must read the data alike
+    check_input_adapters(data, size, read_msgpack());
+
    // return 0 - non-zero return values are reserved for future use
    return 0;
 }
@@ -26,12 +26,30 @@ array data, it performs the following steps:
 The unit tests run the same checks on a fixed corpus (see the "UBJSON round-trip
 invariants" test case), so keep both in sync.

+Finally, it reads the data from a stream, a non-contiguous iterator range, and
+a FILE*, which read byte by byte, and checks that each gives the same value or
+error (id, message, byte position) as the pointer range, which takes the bulk
+fast paths (see check_input_adapters()).
+
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */

 #include "fuzzer_common.hpp"

+namespace
+{
+// json::from_ubjson for check_input_adapters()
+struct read_ubjson
+{
+    template<typename... Args>
+    json operator()(Args&& ... args) const
+    {
+        return json::from_ubjson(std::forward<Args>(args)...);
+    }
+};
+} // namespace
+
 // see http://llvm.org/docs/LibFuzzer.html
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
@@ -96,6 +114,9 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
    }

+    // step 3: the other input adapters must read the data alike
+    check_input_adapters(data, size, read_ubjson());
+
    // return 0 - non-zero return values are reserved for future use
    return 0;
 }
@@ -11,6 +11,14 @@
 #pragma once

 #include <cassert> // assert
+#include <cstddef> // size_t
+#include <cstdint> // uint8_t
+#include <cstdio> // FILE, fmemopen, fclose
+#include <list> // list
+#include <sstream> // istringstream
+#include <string> // string
+#include <utility> // forward
+#include <vector> // vector
 #include <nlohmann/json.hpp>

 using nlohmann::json; // NOLINT(google-global-names-in-headers): shared by all fuzzer drivers
@@ -49,3 +57,89 @@ json parse_without_exceptions(Parse parse, bool& threw)
    }
    return {};
 }
+
+// the outcome of reading an input with exceptions: the serialization of the
+// value, or the id, message, and (for parse errors) byte of the exception
+struct read_outcome
+{
+    std::string value{};
+    int id = 0;
+    std::string what{};
+    std::size_t byte = 0;
+
+    bool operator==(const read_outcome& rhs) const
+    {
+        return value == rhs.value && id == rhs.id && what == rhs.what && byte == rhs.byte;
+    }
+};
+
+inline std::string outcome_value(const json& j)
+{
+    return j.dump(-1, ' ', false, json::error_handler_t::keep);
+}
+
+inline std::string outcome_value(bool b)
+{
+    return b ? "true" : "false";
+}
+
+template<typename Read, typename... Args>
+read_outcome read_with(const Read& parse, Args&& ... args)
+{
+    read_outcome result;
+    try
+    {
+        result.value = outcome_value(parse(std::forward<Args>(args)...));
+    }
+    catch (const json::parse_error& e)
+    {
+        result.id = e.id;
+        result.what = e.what();
+        result.byte = e.byte;
+    }
+    catch (const json::exception& e)
+    {
+        result.id = e.id;
+        result.what = e.what();
+    }
+    return result;
+}
+
+// The contiguous input (a pointer range) takes the bulk fast paths; the other
+// input adapters read byte by byte. Reads @a data through each of them and
+// checks that all give the same value, or the same exception with the same
+// id, message, and byte position.
+//
+// @a parse is called with either an iterator range or a single input (stream
+// or FILE*) and returns the parsed value (or the result of accept()).
+template<typename Read>
+void check_input_adapters(const std::uint8_t* data, std::size_t size, const Read& parse)
+{
+    const read_outcome expected = read_with(parse, data, data + size);
+
+    // stream adapter
+    {
+        std::istringstream stream(std::string(reinterpret_cast<const char*>(data), size));
+        assert(read_with(parse, stream) == expected);
+    }
+
+    // iterator adapter on a non-contiguous range
+    {
+        const std::list<std::uint8_t> list(data, data + size);
+        assert(read_with(parse, list.begin(), list.end()) == expected);
+    }
+
+#if defined(__unix__) || defined(__APPLE__)
+    // FILE* adapter; fmemopen may refuse an empty buffer
+    {
+        std::vector<std::uint8_t> buffer(data, data + size);
+        std::FILE* file = buffer.empty() ? nullptr : fmemopen(buffer.data(), buffer.size(), "rb");
+        if (file != nullptr)
+        {
+            const read_outcome actual = read_with(parse, file);
+            std::fclose(file);
+            assert(actual == expected);
+        }
+    }
+#endif
+}
@@ -9,6 +9,7 @@
 #include "doctest_compatibility.h"

 #include <algorithm>
+#include <numeric>
 #include <nlohmann/json.hpp>
 using nlohmann::json;

@@ -19,6 +19,7 @@

 #include <cctype>
 #include <cstdint>
+#include <limits>
 #include <map>
 #include <string>
 #include <utility>
@@ -1149,3 +1150,157 @@ TEST_CASE("operator<=> of binary values with a different subtype does not depend
    }
 }
 #endif
+
+TEST_CASE("comparison of scalars (inline fast path)")
+{
+    const json::number_integer_t neg = -1;
+    const json::number_integer_t pos = 5;
+    const json::number_unsigned_t big = (std::numeric_limits<json::number_unsigned_t>::max)();
+
+    SECTION("same type")
+    {
+        CHECK(json(pos) == json(pos));
+        CHECK(json(pos) != json(neg));
+        CHECK(json(neg) < json(pos));
+        CHECK_FALSE(json(pos) < json(neg));
+        CHECK_FALSE(json(pos) < json(pos));
+        CHECK(json(pos) <= json(pos));
+
+        CHECK(json(1u) == json(1u));
+        CHECK(json(1u) < json(2u));
+        CHECK_FALSE(json(2u) < json(1u));
+
+        CHECK(json(1.5) == json(1.5));
+        CHECK(json(1.5) < json(2.5));
+        CHECK_FALSE(json(2.5) < json(1.5));
+        CHECK(json(-0.0) == json(0.0));
+    }
+
+    SECTION("mixed number types")
+    {
+        // negative signed vs unsigned must not wrap around
+        CHECK(json(neg) < json(1u));
+        CHECK(json(1u) > json(neg));
+        CHECK(json(neg) != json(big));
+        CHECK(json(neg) < json(big));
+        CHECK_FALSE(json(big) < json(neg));
+
+        CHECK(json(pos) == json(5u));
+        CHECK(json(5u) == json(pos));
+        CHECK(json(pos) < json(6u));
+        CHECK(json(pos) == json(5.0));
+        CHECK(json(5.0) == json(pos));
+        CHECK(json(5u) == json(5.0));
+        CHECK(json(neg) < json(0.5));
+        CHECK(json(0.5) < json(1u));
+    }
+
+    SECTION("boolean and null")
+    {
+        CHECK(json(true) == json(true));
+        CHECK(json(true) != json(false));
+        CHECK(json(false) < json(true));
+        CHECK_FALSE(json(true) < json(false));
+        CHECK_FALSE(json(true) < json(true));
+
+        CHECK(json(nullptr) == json(nullptr));
+        CHECK_FALSE(json(nullptr) < json(nullptr));
+        CHECK(json(nullptr) <= json(nullptr));
+        CHECK(json(nullptr) < json(false));
+        CHECK(json(nullptr) != json(false));
+        CHECK(json(nullptr) != json(0));
+    }
+
+    SECTION("string vs number")
+    {
+        CHECK(json("5") != json(5));
+        CHECK(json(5) != json("5"));
+        CHECK(json(5) < json("5")); // number < string by type order
+        CHECK_FALSE(json("5") < json(5));
+        CHECK(json(1.5) < json(""));
+        CHECK(json("a") == json("a"));
+        CHECK(json("a") < json("b"));
+    }
+
+    SECTION("NaN")
+    {
+        const json nan = std::numeric_limits<json::number_float_t>::quiet_NaN();
+        const json one = 1.0;
+
+        CHECK_FALSE(nan == nan);
+        CHECK(nan != nan);
+        CHECK_FALSE(nan < nan);
+        CHECK_FALSE(nan <= nan);
+        CHECK_FALSE(nan >= nan);
+        CHECK_FALSE(nan > nan);
+
+        CHECK_FALSE(nan == one);
+        CHECK_FALSE(one == nan);
+        CHECK_FALSE(nan < one);
+        CHECK_FALSE(one < nan);
+        CHECK_FALSE(nan <= one);
+        CHECK_FALSE(one <= nan);
+        CHECK_FALSE(nan >= one);
+        CHECK_FALSE(one >= nan);
+
+        // NaN against other number types
+        CHECK_FALSE(nan == json(1));
+        CHECK_FALSE(json(1) == nan);
+        CHECK_FALSE(nan < json(1u));
+        CHECK_FALSE(json(1u) < nan);
+
+#if JSON_HAS_THREE_WAY_COMPARISON
+        CHECK((nan <=> nan) == std::partial_ordering::unordered); // *NOPAD*
+        CHECK((nan <=> one) == std::partial_ordering::unordered); // *NOPAD*
+        CHECK((one <=> nan) == std::partial_ordering::unordered); // *NOPAD*
+        CHECK((one <=> json(2.0)) == std::partial_ordering::less); // *NOPAD*
+        CHECK((json(2.0) <=> one) == std::partial_ordering::greater); // *NOPAD*
+        CHECK((one <=> one) == std::partial_ordering::equivalent); // *NOPAD*
+        CHECK((json(neg) <=> json(1u)) == std::partial_ordering::less); // *NOPAD*
+        CHECK((json(nullptr) <=> json(nullptr)) == std::partial_ordering::equivalent); // *NOPAD*
+        CHECK((json(true) <=> json(false)) == std::partial_ordering::greater); // *NOPAD*
+#endif
+    }
+
+    SECTION("discarded")
+    {
+        const json d(json::value_t::discarded);
+
+        CHECK_FALSE(d == d);
+        CHECK_FALSE(d < d);
+        CHECK_FALSE(d == json(1));
+        CHECK_FALSE(json(1) == d);
+        CHECK_FALSE(d < json(1));
+        CHECK_FALSE(json(1) < d);
+        CHECK_FALSE(d == json(nullptr));
+        CHECK_FALSE(json(nullptr) == d);
+
+#if JSON_HAS_THREE_WAY_COMPARISON
+        CHECK((d <=> d) == std::partial_ordering::unordered); // *NOPAD*
+        CHECK((d <=> json(1)) == std::partial_ordering::unordered); // *NOPAD*
+        CHECK((json(1) <=> d) == std::partial_ordering::unordered); // *NOPAD*
+#endif
+    }
+
+    SECTION("scalar overloads")
+    {
+        CHECK(json(5) == 5);
+        CHECK(5 == json(5));
+        CHECK(json(5) < 6);
+        CHECK(4 < json(5));
+        CHECK(json(1.5) == 1.5);
+        CHECK(json(true) == true);
+        CHECK(json(5) != 6);
+        CHECK(json(1u) == 1.0);
+    }
+
+    SECTION("structured values still compare")
+    {
+        CHECK(json({1, 2}) == json({1, 2}));
+        CHECK(json({1, 2}) < json({1, 3}));
+        CHECK(json({{"a", 1}}) == json({{"a", 1}}));
+        CHECK(json::binary({1, 2}) == json::binary({1, 2}));
+        CHECK(json(1) < json::array());
+        CHECK(json::object() < json::array());
+    }
+}
@@ -8,6 +8,9 @@

 #include "doctest_compatibility.h"

+#include <string>
+#include <vector>
+
 #include <nlohmann/json.hpp>
 using nlohmann::json;

@@ -184,3 +187,193 @@ TEST_CASE("other constructors and destructor")
        }
    }
 }
+
+TEST_CASE("copy constructor and destructor across value types")
+{
+    SECTION("copy of a scalar is independent of the source")
+    {
+        const json src_null = nullptr;
+        const json src_bool = true;
+        const json src_int = -7;
+        const json src_uint = 7u;
+        const json src_float = 2.5;
+
+        json c_null(src_null);
+        json c_bool(src_bool);
+        json c_int(src_int);
+        json c_uint(src_uint);
+        json c_float(src_float);
+
+        CHECK(c_null.is_null());
+        CHECK(c_bool == true);
+        CHECK(c_int == -7);
+        CHECK(c_uint == 7u);
+        CHECK(c_float == 2.5);
+
+        c_int = 8;
+        c_float = 3.5;
+        CHECK(src_int == -7);
+        CHECK(src_float == 2.5);
+    }
+
+    SECTION("copy of an owning value, then mutate the copy")
+    {
+        const json src_string = "hello";
+        const json src_array = {1, 2, 3};
+        const json src_object = {{"a", 1}, {"b", {{"c", 2}}}};
+        const json src_binary = json::binary({1, 2, 3});
+
+        json c_string(src_string);
+        json c_array(src_array);
+        json c_object(src_object);
+        json c_binary(src_binary);
+
+        CHECK(c_string == src_string);
+        CHECK(c_array == src_array);
+        CHECK(c_object == src_object);
+        CHECK(c_binary == src_binary);
+
+        c_string.get_ref<json::string_t&>() += " world";
+        c_array.push_back(4);
+        c_object["b"]["c"] = 3;
+        c_object["d"] = 4;
+        c_binary.get_binary().push_back(4);
+
+        CHECK(src_string == "hello");
+        CHECK(src_array.size() == 3);
+        CHECK(src_object["b"]["c"] == 2);
+        CHECK_FALSE(src_object.contains("d"));
+        CHECK(src_binary.get_binary().size() == 3);
+
+        CHECK(c_string == "hello world");
+        CHECK(c_array.size() == 4);
+        CHECK(c_object["b"]["c"] == 3);
+        CHECK(c_binary.get_binary().size() == 4);
+    }
+
+    SECTION("copy keeps parent pointers valid (JSON_DIAGNOSTICS)")
+    {
+        const json src = {{"a", {1, 2}}, {"b", "x"}};
+        json c(src);
+        c["a"].push_back(3);
+        CHECK(c["a"].size() == 3);
+        CHECK(src["a"].size() == 2);
+    }
+
+    SECTION("vector of mixed types: build, copy, and destroy")
+    {
+        {
+            std::vector<json> v;
+            for (int i = 0; i < 70; ++i)
+            {
+                switch (i % 9)
+                {
+                    case 0:
+                        v.emplace_back(nullptr);
+                        break;
+                    case 1:
+                        v.emplace_back(i % 2 == 0);
+                        break;
+                    case 2:
+                        v.emplace_back(-i);
+                        break;
+                    case 3:
+                        v.emplace_back(static_cast<json::number_unsigned_t>(i));
+                        break;
+                    case 4:
+                        v.emplace_back(i * 0.5);
+                        break;
+                    case 5:
+                        v.emplace_back(std::string(static_cast<std::size_t>(i), 'x'));
+                        break;
+                    case 6:
+                        v.emplace_back(json::array({i, "s", nullptr}));
+                        break;
+                    case 7:
+                        v.emplace_back(json::object({{"k", i}}));
+                        break;
+                    default:
+                        v.emplace_back(json::binary({1, 2, 3}));
+                        break;
+                }
+            }
+            REQUIRE(v.size() == 70);
+
+            std::vector<json> copy(v);
+            CHECK(copy == v);
+
+            // mutating the copy leaves the original alone
+            copy[5] = "changed";
+            copy[6].push_back(1);
+            CHECK(copy != v);
+            CHECK(v[5] == std::string(5, 'x'));
+            CHECK(v[6].size() == 3);
+
+            v.erase(v.begin(), v.begin() + 10);
+            CHECK(v.size() == 60);
+        }
+
+        // destroying the discarded and default-constructed values
+        std::vector<json> w(4);
+        w.emplace_back(json::value_t::discarded);
+        w.emplace_back(json::value_t::object);
+        w.emplace_back(json::value_t::array);
+        w.emplace_back(json::value_t::string);
+        w.emplace_back(json::value_t::binary);
+        CHECK(w.size() == 9);
+    }
+}
+
+TEST_CASE_TEMPLATE("destructor of nested containers", Json, nlohmann::json, nlohmann::ordered_json)
+{
+    SECTION("empty containers")
+    {
+        {
+            Json j = Json::array();
+        }
+        {
+            Json j = Json::object();
+        }
+        {
+            Json j = Json::array({Json::array(), Json::object(), Json::array({Json::array()})});
+        }
+    }
+
+    SECTION("leaves mixed with nested containers")
+    {
+        Json j = Json::object();
+        j["leaf"] = 1;
+        j["str"] = "text";
+        j["empty_a"] = Json::array();
+        j["empty_o"] = Json::object();
+        j["arr"] = Json::array({1, "a", Json::array({1, 2}), Json::object({{"k", Json::array({Json::object()})}}), nullptr});
+        j["obj"] = Json::object({{"x", Json::object({{"y", Json::array({1, Json::object({{"z", 1}})})}})}, {"w", 2}});
+        Json copy = j;
+        CHECK(copy == j);
+        j = Json::array({std::move(copy), j, 3, Json::array()});
+    }
+
+    SECTION("deep nesting")
+    {
+        for (int kind = 0; kind < 3; ++kind)
+        {
+            Json j = 1;
+            for (int i = 0; i < 5000; ++i)
+            {
+                switch (kind)
+                {
+                    case 0:
+                        j = Json::array({std::move(j)});
+                        break;
+                    case 1:
+                        j = Json::object({{"k", std::move(j)}});
+                        break;
+                    default:
+                        // siblings next to the nested child
+                        j = (i % 2 == 0) ? Json::array({1, Json::array(), std::move(j)}) : Json::object({{"a", 1}, {"b", Json::object()}, {"c", std::move(j)}});
+                        break;
+                }
+            }
+        }
+    }
+}
@@ -13,9 +13,11 @@
 #endif

 #define JSON_DIAGNOSTICS 1
+#define JSON_TESTS_PRIVATE

 #include <nlohmann/json.hpp>
 using nlohmann::json;
+using nlohmann::ordered_json;

 #include <map>
 #include <unordered_map>
@@ -631,3 +633,238 @@ TEST_CASE("Better diagnostics past the descent bound of update(), merge_patch()
        CHECK_THROWS_WITH_AS(p->at("y").at(0), expected_y.c_str(), json::type_error);
    }
 }
+
+namespace
+{
+// check that every child's parent pointer points to the containing value
+template<typename BasicJsonType>
+bool parents_consistent(const BasicJsonType& j)
+{
+    bool ok = true;
+    if (j.is_array() || j.is_object())
+    {
+        for (const auto& child : j)
+        {
+            ok = ok && child.m_parent == &j && parents_consistent(child);
+        }
+    }
+    return ok;
+}
+} // namespace
+
+TEST_CASE_TEMPLATE("Parent pointers stay consistent", J, json, ordered_json)
+{
+    SECTION("parse, copy, move, assign, swap")
+    {
+        J j = J::parse(R"({"a":[1,{"b":[2,3]},[4]],"c":{"d":{"e":[]}}})");
+        CHECK(parents_consistent(j));
+
+        J copy(j);
+        CHECK(parents_consistent(copy));
+
+        J moved(std::move(copy));
+        CHECK(parents_consistent(moved));
+
+        J assigned;
+        assigned = j;
+        CHECK(parents_consistent(assigned));
+
+        J other = {1, 2, {{"k", J::array({1, 2})}}};
+        other.swap(assigned);
+        CHECK(parents_consistent(other));
+        CHECK(parents_consistent(assigned));
+    }
+
+    SECTION("push_back growth")
+    {
+        J arr = J::array();
+        for (int i = 0; i < 500; ++i)
+        {
+            arr.push_back(J::array({i}));
+        }
+        CHECK(parents_consistent(arr));
+
+        J obj = J::object();
+        for (int i = 0; i < 500; ++i)
+        {
+            obj.push_back({std::to_string(i), J::array({i})});
+        }
+        CHECK(parents_consistent(obj));
+    }
+
+    SECTION("emplace_back and emplace growth")
+    {
+        J arr = J::array();
+        J obj = J::object();
+        for (int i = 0; i < 500; ++i)
+        {
+            arr.emplace_back(J::array({i}));
+            obj.emplace(std::to_string(i), J::array({i}));
+        }
+        CHECK(parents_consistent(arr));
+        CHECK(parents_consistent(obj));
+    }
+
+    SECTION("operator[] growth and at()")
+    {
+        J obj = J::object();
+        for (int i = 0; i < 500; ++i)
+        {
+            obj[std::to_string(i)] = J::array({i});
+            CHECK(obj[std::to_string(i / 2)].m_parent == &obj);
+        }
+        CHECK(parents_consistent(obj));
+
+        J arr = J::array();
+        for (int i = 0; i < 500; ++i)
+        {
+            arr[static_cast<size_t>(i)] = J::object({{"x", i}});
+        }
+        for (size_t i = 0; i < 500; ++i)
+        {
+            CHECK(arr.at(i).m_parent == &arr);
+        }
+        CHECK(obj.at("3").m_parent == &obj);
+        CHECK(parents_consistent(arr));
+        CHECK(parents_consistent(obj));
+    }
+}
+
+TEST_CASE_TEMPLATE("update() and merge_patch() keep parent pointers and diagnostic paths", J, json, ordered_json)
+{
+    // enough keys to make the vector behind ordered_json reallocate several times
+    const auto make_object = [](int first, int last)
+    {
+        J o = J::object();
+        for (int i = first; i < last; ++i)
+        {
+            o[std::to_string(i)] = J::object({{"x", J::array({i})}});
+        }
+        return o;
+    };
+
+    // const access, so operator[] cannot repair the parent pointers
+    const auto check_path = [](const J & j, const std::string & key)
+    {
+        const std::string expected = "[json.exception.type_error.304] (/" + key + "/x) cannot use at() with array";
+        CHECK_THROWS_WITH_AS(j[key]["x"].at("y"), expected.c_str(), json::type_error);
+    };
+
+    SECTION("update(const_reference)")
+    {
+        J j = make_object(0, 200);
+        j.update(make_object(100, 400));
+        CHECK(j.size() == 400);
+        CHECK(parents_consistent(j));
+        check_path(j, "0");
+        check_path(j, "150");
+        check_path(j, "399");
+    }
+
+    SECTION("update(const_reference, merge_objects)")
+    {
+        J j = make_object(0, 200);
+        j["50"]["y"] = 1;
+        J other = make_object(100, 400);
+        other["50"] = J::object({{"z", J::array({1})}});
+        j.update(other, true);
+        CHECK(j.size() == 400);
+        CHECK(j["50"].size() == 3);
+        CHECK(parents_consistent(j));
+        check_path(j, "0");
+        check_path(j, "399");
+    }
+
+    SECTION("update(first, last)")
+    {
+        J j = make_object(0, 200);
+        J other = make_object(100, 400);
+        j.update(other.begin(), other.end());
+        CHECK(j.size() == 400);
+        CHECK(parents_consistent(j));
+        check_path(j, "0");
+        check_path(j, "399");
+
+        J k = make_object(0, 200);
+        k.update(other.begin(), other.end(), true);
+        CHECK(k.size() == 400);
+        CHECK(parents_consistent(k));
+        check_path(k, "399");
+    }
+
+    SECTION("merge_patch()")
+    {
+        J j = make_object(0, 200);
+        J patch = make_object(100, 400);
+        patch["0"] = nullptr;
+        j.merge_patch(patch);
+        CHECK(j.size() == 399);
+        CHECK_FALSE(j.contains("0"));
+        CHECK(parents_consistent(j));
+        check_path(j, "1");
+        check_path(j, "399");
+    }
+}
+
+namespace
+{
+// an object type that, like a sorted flat map, moves its members when a key is
+// added even if its capacity does not change; it has a capacity() member, but
+// is neither node-based nor nlohmann::ordered_map, so the library must not
+// trust its capacity to tell whether the members moved
+template<class Key, class T, class IgnoredLess = std::less<Key>,
+         class Allocator = std::allocator<std::pair<const Key, T>>>
+             struct relocating_map : nlohmann::ordered_map<Key, T, IgnoredLess, Allocator>
+{
+    using base_type = nlohmann::ordered_map<Key, T, IgnoredLess, Allocator>;
+    using typename base_type::iterator;
+    using typename base_type::Container;
+    using base_type::base_type;
+
+    template<typename... Args>
+    std::pair<iterator, bool> emplace(Args&& ... args)
+    {
+        auto result = base_type::emplace(std::forward<Args>(args)...);
+        const auto index = result.first - this->begin();
+        if (result.second)
+        {
+            // move every member to a new buffer of the same capacity
+            Container relocated;
+            relocated.reserve(this->capacity());
+            for (auto& member : *this)
+            {
+                relocated.emplace_back(member.first, std::move(member.second));
+            }
+            this->Container::swap(relocated);
+        }
+        return {this->begin() + index, result.second};
+    }
+};
+
+using relocating_json = nlohmann::basic_json<relocating_map>;
+} // namespace
+
+TEST_CASE("Parent pointers stay consistent for object types not known to keep their members in place")
+{
+    relocating_json obj = relocating_json::object();
+    for (int i = 0; i < 100; ++i)
+    {
+        obj[std::to_string(i)] = relocating_json::array({i});
+        obj.emplace(std::to_string(i + 1000), relocating_json::array({i}));
+    }
+    CHECK(parents_consistent(obj));
+
+    obj.erase("0");
+    CHECK(parents_consistent(obj));
+
+    relocating_json other = relocating_json::object();
+    for (int i = 0; i < 100; ++i)
+    {
+        other[std::to_string(i + 2000)] = relocating_json::array({i});
+    }
+    obj.update(other);
+    CHECK(parents_consistent(obj));
+
+    obj["1"].push_back(42);
+    CHECK_THROWS_WITH_AS(obj["1"].at(5), "[json.exception.out_of_range.401] (/1) array index 5 is out of range", relocating_json::out_of_range&);
+}
@@ -0,0 +1,474 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+// The fast paths for contiguous input (bulk string scanning, SWAR searches,
+// UTF-8 prefix validation, the 8-digit number loop, the 8-byte indentation
+// skip, the BSON/BON8 bulk string readers) load several bytes at a time. This
+// test places every input directly in front of (or directly behind) an
+// inaccessible page, so reading even one byte outside the input crashes, with
+// or without sanitizers. ASan alone misses over-reads into the slack of the
+// same heap allocation.
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <cstdint>
+#include <cstring>
+#include <string>
+#include <utility>
+#include <vector>
+
+#if defined(_WIN32)
+    #define JSON_TEST_GUARD_PAGE_WINDOWS
+    #ifndef NOMINMAX
+        #define NOMINMAX
+    #endif
+    #ifndef WIN32_LEAN_AND_MEAN
+        #define WIN32_LEAN_AND_MEAN
+    #endif
+    #include <windows.h>
+#elif defined(__unix__) || defined(__APPLE__)
+    #define JSON_TEST_GUARD_PAGE_POSIX
+    #include <sys/mman.h>
+    #include <unistd.h>
+#endif
+
+#if defined(JSON_TEST_GUARD_PAGE_WINDOWS) || defined(JSON_TEST_GUARD_PAGE_POSIX)
+
+namespace
+{
+// Three pages: an inaccessible one, a readable one, an inaccessible one. An
+// input is copied either to the end of the middle page (any read past its last
+// byte faults) or to its start (any read before its first byte faults).
+class guarded_buffer
+{
+  public:
+    guarded_buffer()
+        : page(page_size())
+    {
+#if defined(JSON_TEST_GUARD_PAGE_WINDOWS)
+        void* const p = VirtualAlloc(nullptr, 3 * page, MEM_RESERVE | MEM_COMMIT, PAGE_NOACCESS);
+        REQUIRE(p != nullptr);
+        base = static_cast<unsigned char*>(p);
+        DWORD old_protect = 0;
+        REQUIRE(VirtualProtect(base + page, page, PAGE_READWRITE, &old_protect) != 0);
+#else
+        void* const p = mmap(nullptr, 3 * page, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
+        REQUIRE(p != MAP_FAILED);
+        base = static_cast<unsigned char*>(p);
+        REQUIRE(mprotect(base + page, page, PROT_READ | PROT_WRITE) == 0);
+#endif
+    }
+
+    ~guarded_buffer()
+    {
+#if defined(JSON_TEST_GUARD_PAGE_WINDOWS)
+        VirtualFree(base, 0, MEM_RELEASE);
+#else
+        munmap(base, 3 * page);
+#endif
+    }
+
+    guarded_buffer(const guarded_buffer&) = delete;
+    guarded_buffer& operator=(const guarded_buffer&) = delete;
+    guarded_buffer(guarded_buffer&&) = delete;
+    guarded_buffer& operator=(guarded_buffer&&) = delete;
+
+    // copies @a input so its last byte is the last readable byte
+    const std::uint8_t* at_end(const std::string& input)
+    {
+        REQUIRE(input.size() <= page);
+        unsigned char* const first = base + (2 * page) - input.size();
+        std::memcpy(first, input.data(), input.size());
+        return first;
+    }
+
+    // copies @a input so its first byte is the first readable byte
+    const std::uint8_t* at_start(const std::string& input)
+    {
+        REQUIRE(input.size() <= page);
+        unsigned char* const first = base + page;
+        std::memcpy(first, input.data(), input.size());
+        return first;
+    }
+
+  private:
+    static std::size_t page_size()
+    {
+#if defined(JSON_TEST_GUARD_PAGE_WINDOWS)
+        SYSTEM_INFO info;
+        GetSystemInfo(&info);
+        return static_cast<std::size_t>(info.dwPageSize);
+#else
+        return static_cast<std::size_t>(sysconf(_SC_PAGESIZE));
+#endif
+    }
+
+    std::size_t page = 0;
+    unsigned char* base = nullptr;
+};
+
+// the serialization of the result of @a f, or the exception message; @a f
+// takes the allow_exceptions flag, which is false without exceptions, where
+// an error yields a discarded value instead
+template<typename F>
+std::string outcome(F f)
+{
+#if defined(JSON_NOEXCEPTION)
+    return "value: " + f(false).dump(-1, ' ', false, json::error_handler_t::keep);
+#else
+    try
+    {
+        return "value: " + f(true).dump(-1, ' ', false, json::error_handler_t::keep);
+    }
+    catch (const json::exception& e)
+    {
+        return std::string("error: ") + e.what();
+    }
+#endif
+}
+
+// a SAX handler that only counts events, so sax_parse runs without a DOM
+struct counting_sax : nlohmann::json_sax<json>
+{
+    std::size_t events = 0;
+    std::string error{}; // NOLINT(readability-redundant-member-init)
+
+    bool null() override
+    {
+        return count();
+    }
+    bool boolean(bool /*val*/) override
+    {
+        return count();
+    }
+    bool number_integer(number_integer_t /*val*/) override
+    {
+        return count();
+    }
+    bool number_unsigned(number_unsigned_t /*val*/) override
+    {
+        return count();
+    }
+    bool number_float(number_float_t /*val*/, const string_t& /*s*/) override
+    {
+        return count();
+    }
+    bool string(string_t& /*val*/) override
+    {
+        return count();
+    }
+    bool binary(binary_t& /*val*/) override
+    {
+        return count();
+    }
+    bool start_object(std::size_t /*elements*/) override
+    {
+        return count();
+    }
+    bool key(string_t& /*val*/) override
+    {
+        return count();
+    }
+    bool end_object() override
+    {
+        return count();
+    }
+    bool start_array(std::size_t /*elements*/) override
+    {
+        return count();
+    }
+    bool end_array() override
+    {
+        return count();
+    }
+    bool parse_error(std::size_t position, const std::string& /*last_token*/, const nlohmann::detail::exception& ex) override
+    {
+        error = std::to_string(position) + " " + ex.what();
+        return false;
+    }
+
+  private:
+    bool count()
+    {
+        ++events;
+        return true;
+    }
+};
+
+// all prefixes of each seed, so the input ends at every byte of it
+std::vector<std::string> all_prefixes(const std::vector<std::string>& seeds)
+{
+    std::vector<std::string> result;
+    for (const auto& seed : seeds)
+    {
+        for (std::size_t n = 0; n <= seed.size(); ++n)
+        {
+            result.push_back(seed.substr(0, n));
+        }
+    }
+    return result;
+}
+
+std::vector<std::string> json_seeds()
+{
+    std::vector<std::string> seeds =
+    {
+        // string runs: ASCII, escapes, \u escapes, surrogate pairs
+        "\"abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ\"",
+        R"("ab\ncd\"ef\\gh\u00e4ij\uD83D\uDE00kl\u12")",
+        // 2-, 3- and 4-byte UTF-8 sequences, then invalid UTF-8
+        std::string("\"\xC3\xA4\xE2\x82\xAC\xF0\x9F\x98\x80\xC3\xA4\xE2\x82\xAC\xF0\x9F\x98\x80") + "abcdefgh\"",
+        "\"abcdefgh\xC3\x28 \xED\xA0\x80 \xF4\x90\x80\x80 \xF8 \xC0\xAF\"",
+        std::string("\"abcdefg\x01") + "abcdefgh\"",
+        // numbers, so the 8-digit loop runs up to the end
+        "12345678",
+        "1234567890123456",
+        "12345678901234567890123",
+        "-0.000000001234567890123456789",
+        "3.14159265358979323846264338327950288e+100",
+        "-1.2345678901234567e-12",
+        "1E-5",
+        "[1.5,2e10,-3E-5,0.000000001,123456789012345678]",
+        // literals
+        "[true,false,null]",
+        // comments (only parsed with ignore_comments)
+        "/* comment */ [1, // line comment\n 2] /**/",
+        // a pretty-printed document
+        json::parse(R"({"a": [1, 2.5, "three", {"b": null, "c": [true, false]}], "d": {"e": {"f": {"g": "h"}}}})").dump(4),
+        json::parse(R"({"a": [1, 2.5, "three", {"b": null, "c": [true, false]}], "d": {"e": {"f": {"g": "h"}}}})").dump(8, '\t'),
+    };
+
+    // indentation runs of every length, with and without a closing bracket
+    for (std::size_t n = 0; n <= 20; ++n)
+    {
+        seeds.push_back("[\n" + std::string(n, ' ') + "1,\n" + std::string(n, ' ') + "2\n]");
+    }
+
+    return all_prefixes(seeds);
+}
+
+// a value whose binary serializations contain long strings and keys, numbers
+// of every width, and nested containers
+json binary_document()
+{
+    json j;
+    j["a key that is longer than eight bytes"] = "a string value that is longer than eight bytes";
+    j["\xC3\xA4\xE2\x82\xAC\xF0\x9F\x98\x80"] = "\xF0\x9F\x98\x80\xE2\x82\xAC\xC3\xA4 utf-8 0123456789";
+    j["numbers"] = {0, 1, -1, 255, -256, 65536, -2147483649LL, 4294967296ULL, 1.5, -2.25e100};
+    j["nested"] = {{"x", {{"y", {true, false, nullptr}}}}};
+    j["s"] = "";
+    return j;
+}
+
+// readers for check_binary(), callable with a container or an iterator range
+// followed by the allow_exceptions flag
+#define JSON_TEST_GUARD_PAGE_READER(name, from)                                     \
+    struct name                                                                     \
+    {                                                                               \
+        template<typename... Args>                                                  \
+        json operator()(bool allow_exceptions, Args&& ... args) const               \
+        {                                                                           \
+            return json::from(std::forward<Args>(args)..., true, allow_exceptions); \
+        }                                                                           \
+    };
+JSON_TEST_GUARD_PAGE_READER(read_bson, from_bson)
+JSON_TEST_GUARD_PAGE_READER(read_bon8, from_bon8)
+JSON_TEST_GUARD_PAGE_READER(read_cbor, from_cbor)
+JSON_TEST_GUARD_PAGE_READER(read_msgpack, from_msgpack)
+JSON_TEST_GUARD_PAGE_READER(read_ubjson, from_ubjson)
+JSON_TEST_GUARD_PAGE_READER(read_bjdata, from_bjdata)
+#undef JSON_TEST_GUARD_PAGE_READER
+
+// reads every prefix of @a bytes at both ends of the guarded page and from a
+// std::string, which must give the same outcome
+template<typename Reader>
+void check_binary(guarded_buffer& guard, const std::vector<std::uint8_t>& bytes, Reader parse)
+{
+    for (const auto& input : all_prefixes({std::string(bytes.begin(), bytes.end())}))
+    {
+        CAPTURE(input)
+        const std::string expected = outcome([&](bool allow)
+        {
+            return parse(allow, input);
+        });
+        for (int placement = 0; placement < 2; ++placement)
+        {
+            const std::uint8_t* const first = placement == 0 ? guard.at_end(input) : guard.at_start(input);
+            CHECK(outcome([&](bool allow)
+            {
+                return parse(allow, first, first + input.size());
+            }) == expected);
+        }
+    }
+}
+
+// parse_float_native() at both ends of the guarded page, compared bit for bit
+// with converting the same token from a std::string
+template<typename FloatType>
+void check_float_native(guarded_buffer& guard, const std::string& token)
+{
+    const std::size_t decimal_point = token.find('.');
+    const std::size_t exponent = token.find_first_of("eE");
+    const std::size_t mantissa_end = exponent == std::string::npos ? token.size() : exponent;
+    const FloatType expected = nlohmann::detail::parse_float_native<FloatType>(token.data(), token.data() + token.size(), decimal_point, mantissa_end);
+    for (int placement = 0; placement < 2; ++placement)
+    {
+        const char* const first = reinterpret_cast<const char*>(placement == 0 ? guard.at_end(token) : guard.at_start(token));
+        const FloatType value = nlohmann::detail::parse_float_native<FloatType>(first, first + token.size(), decimal_point, mantissa_end);
+        CHECK(std::memcmp(&value, &expected, sizeof(value)) == 0);
+    }
+}
+} // namespace
+
+TEST_CASE("guard page")
+{
+    guarded_buffer guard;
+
+    SECTION("string scanning")
+    {
+        // fills that drive each function to a different stop
+        const std::vector<std::string> fills =
+        {
+            std::string(64, 'a'),
+            std::string(64, '"'),
+            std::string(64, '\\'),
+            std::string(64, '\x01'),
+            std::string(64, '\x7F'),
+            std::string(64, '\xFF'),
+        };
+        std::vector<std::string> patterns = fills;
+        {
+            std::string utf8;
+            while (utf8.size() < 64)
+            {
+                utf8 += "\xC3\xA4\xE2\x82\xAC\xF0\x9F\x98\x80" "ab";
+            }
+            patterns.push_back(utf8);
+        }
+        {
+            std::string bytes;
+            for (unsigned int i = 0; i < 64; ++i)
+            {
+                bytes.push_back(static_cast<char>((i * 37u) & 0xFFu));
+            }
+            patterns.push_back(bytes);
+        }
+
+        for (const auto& pattern : patterns)
+        {
+            for (std::size_t n = 0; n <= 64; ++n)
+            {
+                const std::string input = pattern.substr(0, n);
+                for (int placement = 0; placement < 2; ++placement)
+                {
+                    const unsigned char* const p = placement == 0 ? guard.at_end(input) : guard.at_start(input);
+
+                    CHECK(nlohmann::detail::find_string_special(p, n) <= n);
+                    CHECK(nlohmann::detail::find_ascii_copyable_run(p, n) <= n);
+                    CHECK(nlohmann::detail::valid_utf8_prefix(p, n) <= n);
+#if defined(JSON_USE_SIMDUTF) && defined(JSON_HAS_CPP_17)
+                    CHECK(nlohmann::detail::find_string_delimiter(p, n) <= n);
+#endif
+                    CHECK(nlohmann::detail::string_bulk_run(p, n) <= n);
+                    CHECK(nlohmann::detail::scalar_string_bulk_run(p, n) <= n);
+                    for (std::size_t i = 0; i < n; ++i)
+                    {
+                        CHECK(nlohmann::detail::validate_one_utf8(p + i, n - i) <= n - i);
+                    }
+                }
+            }
+        }
+    }
+
+    SECTION("float conversion")
+    {
+        // the lexer converts floats from its token buffer, so the JSON section
+        // below never places a float token at the page boundary; this calls the
+        // conversion directly: the 8-digit loops of parse_float_significand()
+        // and digit_comparison() read up to the end of the token
+        const std::vector<std::string> tokens = all_prefixes(
+        {
+            "1234567812345678123456781234567812345678",
+            "-1.2345678901234567890123456789e-123",
+            "0.00000000000000000000000000000000000001",
+            "98765432.10987654",
+            "123456789012345678901234567890e-30",
+            // halfway between 1 and the next double, then just above it
+            "1.00000000000000011102230246251565404236316680908203125",
+            "1.000000000000000111022302462515654042363166809082031250000000001",
+        });
+        for (const auto& token : tokens)
+        {
+            // only complete number tokens: the conversion expects validated input
+            if (!token.empty() && json::accept(token))
+            {
+                CAPTURE(token)
+                check_float_native<double>(guard, token);
+                check_float_native<float>(guard, token);
+            }
+        }
+    }
+
+    SECTION("JSON")
+    {
+        for (const auto& input : json_seeds())
+        {
+            CAPTURE(input)
+            const std::string expected = outcome([&](bool allow)
+            {
+                return json::parse(input, nullptr, allow);
+            });
+            const std::string expected_comments = outcome([&](bool allow)
+            {
+                return json::parse(input, nullptr, allow, true);
+            });
+            const bool expected_accept = json::accept(input);
+            counting_sax expected_sax;
+            const bool expected_sax_result = json::sax_parse(input, &expected_sax);
+
+            for (int placement = 0; placement < 2; ++placement)
+            {
+                const std::uint8_t* const first = placement == 0 ? guard.at_end(input) : guard.at_start(input);
+                const std::uint8_t* const last = first + input.size();
+
+                CHECK(outcome([&](bool allow)
+                {
+                    return json::parse(first, last, nullptr, allow);
+                }) == expected);
+                CHECK(outcome([&](bool allow)
+                {
+                    return json::parse(first, last, nullptr, allow, true);
+                }) == expected_comments);
+                CHECK(json::accept(first, last) == expected_accept);
+
+                counting_sax sax;
+                CHECK(json::sax_parse(first, last, &sax) == expected_sax_result);
+                CHECK(sax.events == expected_sax.events);
+                CHECK(sax.error == expected_sax.error);
+            }
+        }
+    }
+
+    SECTION("binary formats")
+    {
+        // every prefix ends inside a value, e.g., inside a BSON key or BON8
+        // string without its terminator
+        const json j = binary_document();
+        check_binary(guard, json::to_bson(j), read_bson());
+        check_binary(guard, json::to_bon8(j), read_bon8());
+        check_binary(guard, json::to_cbor(j), read_cbor());
+        check_binary(guard, json::to_msgpack(j), read_msgpack());
+        check_binary(guard, json::to_ubjson(j), read_ubjson());
+        check_binary(guard, json::to_bjdata(j), read_bjdata());
+    }
+}
+
+#endif
@@ -10,6 +10,8 @@

 #define JSON_TESTS_PRIVATE
 #include <nlohmann/json.hpp>
+#include <string>
+#include <vector>
 using nlohmann::json;

 TEST_CASE("iterators 1")
@@ -1628,3 +1630,108 @@ TEST_CASE("iterators 1")
        }
    }
 }
+
+TEST_CASE_TEMPLATE("reverse iteration and member access", Json, nlohmann::json, nlohmann::ordered_json)
+{
+    SECTION("array: -- and rbegin/rend")
+    {
+        Json j = {1, 2, 3, 4};
+
+        auto it = j.end();
+        std::vector<int> seen;
+        while (it != j.begin())
+        {
+            --it;
+            seen.push_back(it->template get<int>());
+        }
+        CHECK(seen == std::vector<int> {4, 3, 2, 1});
+
+        auto it2 = j.end();
+        auto old = it2--;
+        CHECK(old == j.end());
+        CHECK(*it2 == 4);
+
+        seen.clear();
+        for (auto r = j.rbegin(); r != j.rend(); ++r)
+        {
+            seen.push_back(r->template get<int>());
+        }
+        CHECK(seen == std::vector<int> {4, 3, 2, 1});
+
+        seen.clear();
+        for (auto r = j.crbegin(); r != j.crend(); ++r)
+        {
+            seen.push_back(*r);
+        }
+        CHECK(seen == std::vector<int> {4, 3, 2, 1});
+    }
+
+    SECTION("object: -- and rbegin/rend")
+    {
+        Json j = {{"a", 1}, {"b", 2}, {"c", 3}};
+        // order of keys depends on the object type; use the forward order as reference
+        std::vector<std::string> fwd;
+        for (auto it = j.begin(); it != j.end(); ++it)
+        {
+            fwd.push_back(it.key());
+        }
+        std::vector<std::string> rev(fwd.rbegin(), fwd.rend());
+
+        std::vector<std::string> seen;
+        auto it = j.end();
+        while (it != j.begin())
+        {
+            --it;
+            seen.push_back(it.key());
+        }
+        CHECK(seen == rev);
+
+        auto it2 = j.end();
+        auto old = it2--;
+        CHECK(old == j.end());
+        CHECK(it2.key() == rev.front());
+
+        seen.clear();
+        for (auto r = j.rbegin(); r != j.rend(); ++r)
+        {
+            seen.push_back(r.key());
+        }
+        CHECK(seen == rev);
+    }
+
+    SECTION("object: operator-> reads and writes the mapped value")
+    {
+        Json j = {{"a", 1}, {"s", "str"}};
+        auto it = j.find("s");
+        REQUIRE(it != j.end());
+        CHECK(it->is_string());
+        CHECK(it->size() == 1);
+        *it = Json::array({1, 2});
+        CHECK(it->is_array());
+        it->push_back(3);
+        CHECK(j["s"].size() == 3);
+
+        const Json& cj = j;
+        auto cit = cj.find("a");
+        REQUIRE(cit != cj.end());
+        CHECK(cit->is_number_integer());
+        CHECK(cit->template get<int>() == 1);
+    }
+
+    SECTION("primitives: -- and ->")
+    {
+        Json j = 42;
+        auto it = j.end();
+        --it;
+        CHECK(it == j.begin());
+        CHECK(it->template get<int>() == 42);
+    }
+
+    SECTION("comparing iterators of different containers throws")
+    {
+        Json a = {1, 2};
+        Json b = {1, 2};
+        CHECK_THROWS_WITH_AS(a.begin() == b.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", nlohmann::json::invalid_iterator);
+        CHECK_THROWS_WITH_AS(a.begin() < b.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", nlohmann::json::invalid_iterator);
+    }
+}
@@ -2066,3 +2066,40 @@ TEST_CASE("JSON patch - every operation on ordered_json")
        }
    }
 }
+
+TEST_CASE_TEMPLATE("JSON patch - diff round trip on hand-made documents", Json, nlohmann::json, nlohmann::ordered_json)
+{
+    const auto roundtrip = [](const Json & a, const Json & b)
+    {
+        CAPTURE(a.dump())
+        CAPTURE(b.dump())
+        const Json p = Json::diff(a, b);
+        CHECK(a.patch(p) == b);
+        CHECK(Json::diff(b, b).empty());
+    };
+
+    SECTION("reordered keys")
+    {
+        const Json a = Json::parse(R"({"x":1,"y":2,"z":{"p":1,"q":2}})");
+        const Json b = Json::parse(R"({"z":{"q":2,"p":1},"y":2,"x":1})");
+        roundtrip(a, b);
+        roundtrip(b, a);
+    }
+
+    SECTION("nested add, remove and replace")
+    {
+        const Json a = Json::parse(R"({"a":[1,2,{"k":"v","gone":true}],"b":{"c":{"d":1}},"e":"s"})");
+        const Json b = Json::parse(R"({"a":[1,3,{"k":"w","new":[]}],"b":{"c":{"d":[1,2]}},"f":null})");
+        roundtrip(a, b);
+        roundtrip(b, a);
+    }
+
+    SECTION("arrays of different length and type changes")
+    {
+        roundtrip(Json::parse("[1,2,3,4,5]"), Json::parse("[1,3]"));
+        roundtrip(Json::parse("[1]"), Json::parse("[1,[2],{\"a\":3}]"));
+        roundtrip(Json::parse("[]"), Json::parse("{}"));
+        roundtrip(Json::parse("{\"a\":[]}"), Json::parse("{\"a\":{}}"));
+        roundtrip(Json(1), Json::parse("[1]"));
+    }
+}
@@ -23,8 +23,14 @@ using nlohmann::json;
    using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 #endif

+#include <cerrno>
+#include <cstdlib>
+#include <limits>
 #include <map>
+#include <random>
 #include <sstream>
+#include <string>
+#include <vector>

 TEST_CASE("JSON pointers")
 {
@@ -1071,3 +1077,242 @@ TEST_CASE("flatten of structured values")
              R"({"/z":"s","/a~1b/~0":1,"/a~1b/k":null,"/a/0":1,"/a/1/c":null,"/a/1/b":null,"/a/2/0/x~0~1/0":true,"/a/2/0/x~0~1/1":null,"/a/2/0/w":2})");
    }
 }
+
+TEST_CASE("flatten of ordered_json")
+{
+    using nlohmann::ordered_json;
+
+    SECTION("keeps the document order of the leaves")
+    {
+        const ordered_json j = ordered_json::parse(R"({
+            "z": 1, "a": {"y": [true, null, {}], "b": "x", "": []},
+            "m~n": 2.5, "o/p": {"k": {}}, "0": [[1], [2, 3]]
+        })");
+
+        const ordered_json flat = j.flatten();
+        std::vector<std::string> keys;
+        for (const auto& el : flat.items())
+        {
+            keys.push_back(el.key());
+        }
+        const std::vector<std::string> expected =
+        {
+            "/z", "/a/y/0", "/a/y/1", "/a/y/2", "/a/b", "/a/", "/m~0n", "/o~1p/k", "/0/0/0", "/0/1/0", "/0/1/1"
+        };
+        CHECK(keys == expected);
+        CHECK(flat.size() == expected.size());
+        CHECK(flat["/m~0n"] == 2.5);
+        CHECK(flat["/a/y/2"].is_null());
+    }
+
+    SECTION("round-trips and agrees with json")
+    {
+        ordered_json j;
+        for (int i = 0; i < 200; ++i)
+        {
+            j["k" + std::to_string(i)] = {{"v", i}, {"l", {i, i + 1, "s"}}};
+        }
+        const ordered_json flat = j.flatten();
+        CHECK(flat.size() == 800);
+        CHECK(flat.unflatten() == j);
+
+        // same entries as for a sorted object
+        const nlohmann::json plain = nlohmann::json::parse(j.dump());
+        CHECK(nlohmann::json::parse(flat.dump()) == plain.flatten());
+    }
+
+    SECTION("primitive and empty root")
+    {
+        CHECK(ordered_json(1).flatten() == ordered_json({{"", 1}}));
+        CHECK(ordered_json::array().flatten() == ordered_json({{"", nullptr}}));
+    }
+}
+namespace
+{
+// reference implementation of the array index rules (RFC 6901, Sect. 4) based on strtoull
+enum class index_class
+{
+    ok,
+    leading_zero,
+    not_a_number,
+    unresolved,
+    exceeds_size_type
+};
+
+index_class classify_index(const std::string& s, std::size_t& idx)
+{
+    if (s.size() > 1 && s[0] == '0')
+    {
+        return index_class::leading_zero;
+    }
+    if (!s.empty() && s != "-" && !(s[0] >= '0' && s[0] <= '9'))
+    {
+        return index_class::not_a_number;
+    }
+    char* end = nullptr;
+    errno = 0;
+    const unsigned long long res = std::strtoull(s.c_str(), &end, 10); // NOLINT(runtime/int)
+    if (end == s.c_str() || errno == ERANGE || static_cast<std::size_t>(end - s.c_str()) != s.size())
+    {
+        return index_class::unresolved;
+    }
+    if (res >= static_cast<unsigned long long>((std::numeric_limits<std::size_t>::max)())) // NOLINT(runtime/int)
+    {
+        return index_class::exceeds_size_type;
+    }
+    idx = static_cast<std::size_t>(res);
+    return index_class::ok;
+}
+
+// the observable behavior of json_pointer::at() and contains() for an array index token
+void check_index_token(const std::string& token)
+{
+    const json array = {10, 20, 30};
+    const json::json_pointer ptr("/" + token);
+
+    std::size_t idx = 0;
+    const auto cls = classify_index(token, idx);
+    const bool exists = cls == index_class::ok && idx < array.size();
+
+    CAPTURE(token)
+    CHECK(array.contains(ptr) == (exists && token != "-"));
+
+    if (token == "-")
+    {
+        CHECK_THROWS_AS(array.at(ptr), json::out_of_range&);
+        return;
+    }
+
+    switch (cls)
+    {
+        case index_class::leading_zero:
+            CHECK_THROWS_AS(array.at(ptr), json::parse_error&);
+            break;
+        case index_class::not_a_number:
+            CHECK_THROWS_AS(array.at(ptr), json::parse_error&);
+            break;
+        case index_class::unresolved:
+        case index_class::exceeds_size_type:
+            CHECK_THROWS_AS(array.at(ptr), json::out_of_range&);
+            break;
+        case index_class::ok:
+        default:
+            if (exists)
+            {
+                CHECK(array.at(ptr) == array[idx]);
+            }
+            else
+            {
+                CHECK_THROWS_AS(array.at(ptr), json::out_of_range&);
+            }
+            break;
+    }
+}
+} // namespace
+
+TEST_CASE("JSON pointer array index tokens match strtoull semantics")
+{
+    SECTION("boundary values")
+    {
+        const std::string max_digits = std::to_string((std::numeric_limits<std::size_t>::max)());
+        const std::vector<std::string> tokens =
+        {
+            "", "-", "0", "1", "2", "3", "00", "01", "007", "+1", "-1", " 1", "1 ", "1a", "a1", "0x1", "1e1", "1.0",
+            "999999999", "1000000000", "99999999999999999", "999999999999999999", "1000000000000000000",
+            "9999999999999999999", "18446744073709551614", max_digits, "18446744073709551616",
+            "99999999999999999999999", "000000000000000000000"
+        };
+        for (const auto& token : tokens)
+        {
+            check_index_token(token);
+        }
+    }
+
+    SECTION("random tokens")
+    {
+        std::mt19937 gen(42);
+        const std::string alphabet = "0123456789012345678901234567890123456789-+ ex";
+        for (int i = 0; i < 5000; ++i)
+        {
+            std::string token(static_cast<std::size_t>(gen() % 23), '0');
+            for (auto& c : token)
+            {
+                c = alphabet[gen() % alphabet.size()];
+            }
+            check_index_token(token);
+        }
+    }
+}
+
+TEST_CASE("JSON pointer operations on pointers with escaped tokens")
+{
+    const std::vector<std::string> strings =
+    {
+        "", "/", "//", "/a", "/a/b", "/a~1b", "/~0", "/~01", "/~10", "/a~0~1/b/", "/0/1/2", "/ ", "/a/", "/~1/~0"
+    };
+
+    for (const auto& str : strings)
+    {
+        CAPTURE(str)
+        const json::json_pointer ptr(str);
+        CHECK(ptr.to_string() == str);
+        CHECK(ptr / "x" / "y" / std::size_t{3} == json::json_pointer(str + "/x/y/3"));
+        CHECK(ptr.parent_pointer() == (str.empty() ? ptr : json::json_pointer(str.substr(0, str.rfind('/')))));
+
+        // comparison with a string, in place, and with every other pointer
+#if !defined(JSON_TEST_DEPRECATED_FUNCTIONS_DELETED)
+        for (const auto& other : strings)
+        {
+            CAPTURE(other)
+            CHECK((ptr == other) == (str == other));
+            CHECK((other == ptr) == (str == other));
+            CHECK((ptr != other) == (str != other));
+        }
+        CHECK_THROWS_AS(ptr == "x", json::parse_error&);
+        CHECK_THROWS_AS(ptr == "/~", json::parse_error&);
+        CHECK_THROWS_AS(ptr == "/b/~2", json::parse_error&);
+#endif
+    }
+}
+
+TEST_CASE("JSON pointer lookups")
+{
+    json j = {{"a", {{"b", {1, 2, 3}}}}, {"", 7}, {"~/", {{"x", nullptr}}}};
+    const json& cj = j;
+
+    CHECK(cj[json::json_pointer("/a/b/2")] == 3);
+    CHECK(cj.at(json::json_pointer("/a/b/1")) == 2);
+    CHECK(cj.at(json::json_pointer("/")) == 7);
+    CHECK(cj.contains(json::json_pointer("/~0~1/x")));
+    CHECK(!cj.contains(json::json_pointer("/a/c")));
+    CHECK(cj.value(json::json_pointer("/a/b/0"), 5) == 1);
+    CHECK(cj.value(json::json_pointer("/a/b/3"), 5) == 5);
+    CHECK(cj.value(json::json_pointer("/a/zz"), 5) == 5);
+
+    CHECK_THROWS_AS(cj.at(json::json_pointer("/a/c")), json::out_of_range&);
+    CHECK_THROWS_AS(cj.at(json::json_pointer("/a/b/3")), json::out_of_range&);
+
+    // non-const access reuses existing entries and creates missing ones
+    j[json::json_pointer("/a/b/1")] = 20;
+    j[json::json_pointer("/n/m")] = 1;
+    CHECK(j["a"]["b"] == json({1, 20, 3}));
+    CHECK(j["n"]["m"] == 1);
+}
+
+TEST_CASE("JSON patch with moves and copies")
+{
+    json doc = {{"a", {{"b", {1, 2, 3}}}}, {"c", {{"d", "x"}}}};
+
+    CHECK(doc.patch(json::parse(R"([{"op":"move","from":"/a/b","path":"/c/e"}])")) ==
+          json::parse(R"({"a":{},"c":{"d":"x","e":[1,2,3]}})"));
+    CHECK(doc.patch(json::parse(R"([{"op":"copy","from":"/a/b","path":"/c/e"}])")) ==
+          json::parse(R"({"a":{"b":[1,2,3]},"c":{"d":"x","e":[1,2,3]}})"));
+    CHECK(doc.patch(json::parse(R"([{"op":"move","from":"/a/b/0","path":"/a/b/2"}])")) ==
+          json::parse(R"({"a":{"b":[2,3,1]},"c":{"d":"x"}})"));
+
+    // a failing move leaves a copy-patched document untouched
+    CHECK_THROWS_AS(doc.patch(json::parse(R"([{"op":"move","from":"","path":""}])")), json::out_of_range&);
+    json inplace = doc;
+    CHECK_THROWS_AS(inplace.patch_inplace(json::parse(R"([{"op":"move","from":"","path":""}])")), json::out_of_range&);
+    CHECK(inplace == doc);
+}
@@ -0,0 +1,201 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+
+#include <cstdint>
+#include <functional>
+#include <limits>
+#include <string>
+#include <vector>
+
+// basic_json with the same type for number_integer_t and number_unsigned_t
+// (#2573): every integer is stored as number_integer
+
+namespace
+{
+
+template<typename IntegerType>
+using same_types_json = nlohmann::json::with_integers_t<IntegerType, IntegerType>;
+
+using json64 = same_types_json<std::int64_t>;
+using json32 = same_types_json<std::int32_t>;
+
+} // namespace
+
+TEST_CASE_TEMPLATE("same type for number_integer_t and number_unsigned_t", Json, json64, json32)
+{
+    using integer_t = typename Json::number_integer_t;
+    using limits = std::numeric_limits<integer_t>;
+
+    SECTION("parsing stores integers as number_integer")
+    {
+        const Json j = Json::parse("[0, 1, -1, 2147483647, -2147483648]");
+        for (const auto& element : j)
+        {
+            CHECK(element.is_number_integer());
+            CHECK(!element.is_number_unsigned());
+            CHECK(element.type() == nlohmann::detail::value_t::number_integer);
+        }
+        CHECK(j[1].template get<integer_t>() == 1);
+        CHECK(j[2].template get<integer_t>() == -1);
+        CHECK(j[3].template get<integer_t>() == 2147483647);
+        CHECK(j[4].template get<std::int64_t>() == -2147483648LL);
+    }
+
+    SECTION("integers above the maximum are parsed as floats")
+    {
+        // a positive literal is parsed as unsigned first; it must not wrap
+        // around to a negative number_integer_t
+        const auto above_max = std::to_string(static_cast<std::uint64_t>(limits::max()) + 1);
+        const Json j1 = Json::parse(above_max);
+        CHECK(j1.is_number_float());
+        CHECK(j1.template get<double>() == static_cast<double>(static_cast<std::uint64_t>(limits::max()) + 1));
+
+        const Json j2 = Json::parse("18446744073709551615");
+        CHECK(j2.is_number_float());
+        CHECK(j2.template get<double>() == 18446744073709551615.0);
+
+        const Json j3 = Json::parse(std::to_string(limits::max()));
+        CHECK(j3.is_number_integer());
+        CHECK(j3.template get<integer_t>() == limits::max());
+    }
+
+    SECTION("serialization of the extremes")
+    {
+        CHECK(Json(limits::max()).dump() == std::to_string(limits::max()));
+        // the absolute value of the minimum does not fit into number_unsigned_t
+        CHECK(Json(limits::min()).dump() == std::to_string(limits::min()));
+        CHECK(Json::parse(std::to_string(limits::min())) == Json(limits::min()));
+        CHECK(Json(0).dump() == "0");
+    }
+
+    SECTION("construction from unsigned types")
+    {
+        const Json j1 = 5u;
+        CHECK(j1.is_number_integer());
+        CHECK(!j1.is_number_unsigned());
+        CHECK(j1 == 5);
+
+        const Json j2 = static_cast<std::uint8_t>(200);
+        CHECK(j2.is_number_integer());
+        CHECK(j2.template get<integer_t>() == 200);
+
+        const Json j3 = std::vector<unsigned> {1, 2, 3};
+        CHECK(j3.dump() == "[1,2,3]");
+        CHECK(j3[0].is_number_integer());
+
+        const Json j4 = true;
+        CHECK(j4.is_boolean());
+    }
+
+    SECTION("value_t::number_unsigned creates a number_integer")
+    {
+        const Json j(nlohmann::detail::value_t::number_unsigned);
+        CHECK(j.is_number_integer());
+        CHECK(!j.is_number_unsigned());
+        CHECK(j == 0);
+        CHECK(j.dump() == "0");
+    }
+
+    SECTION("conversions")
+    {
+        Json j = 42;
+        CHECK(j.template get<unsigned>() == 42u);
+        CHECK(j.template get<std::uint64_t>() == 42u);
+        CHECK(j.template get<int>() == 42);
+        CHECK(j.template get<double>() == 42.0);
+        CHECK(j.template get_ptr<integer_t*>() != nullptr);
+        CHECK(*j.template get_ptr<integer_t*>() == 42);
+        CHECK(j.template get_ref<integer_t&>() == 42);
+        j.template get_ref<integer_t&>() = 43;
+        CHECK(j == 43);
+
+        integer_t i = 0;
+        j.get_to(i);
+        CHECK(i == 43);
+
+        const Json object = {{"a", 1}};
+        CHECK(object.value("a", 0u) == 1u);
+        CHECK(object.value("b", 7u) == 7u);
+    }
+
+    SECTION("conversion from a basic_json with distinct types")
+    {
+        const nlohmann::json j = {1, 2u, -3, 4.5};
+        CHECK(j[1].is_number_unsigned());
+        const Json converted = j;
+        CHECK(converted.dump() == "[1,2,-3,4.5]");
+        CHECK(converted[1].is_number_integer());
+        CHECK(!converted[1].is_number_unsigned());
+
+        const nlohmann::json back = converted;
+        CHECK(back == j);
+    }
+
+    SECTION("comparison and hashing")
+    {
+        const Json j1 = 1;
+        const Json j2 = 2u;
+        CHECK(j1 < j2);
+        CHECK(j1 != j2);
+        CHECK(j2 == 2);
+        CHECK(j2 == 2u);
+        CHECK(j1 < 1.5);
+        CHECK(Json(-1) < Json(0u));
+        CHECK(std::hash<Json> {}(Json(5u)) == std::hash<Json> {}(Json(5)));
+    }
+
+    SECTION("JSON Patch, diff, and flatten")
+    {
+        const Json source = Json::parse(R"({"a": [1, 2, 3], "b": 4})");
+        const Json target = Json::parse(R"({"a": [1, 5], "c": 6})");
+        CHECK(source.patch(Json::diff(source, target)) == target);
+        CHECK(source.flatten().unflatten() == source);
+    }
+
+    SECTION("binary formats")
+    {
+        const Json j = {{"min", limits::min()}, {"max", limits::max()}, {"zero", 0}, {"small", 100}, {"negative", -100}, {"float", 1.5}};
+
+        CHECK(Json::from_cbor(Json::to_cbor(j)) == j);
+        CHECK(Json::from_msgpack(Json::to_msgpack(j)) == j);
+        CHECK(Json::from_ubjson(Json::to_ubjson(j)) == j);
+        CHECK(Json::from_bjdata(Json::to_bjdata(j)) == j);
+        CHECK(Json::from_bson(Json::to_bson(j)) == j);
+        CHECK(Json::from_bon8(Json::to_bon8(j)) == j);
+
+        for (const auto& element : Json::from_cbor(Json::to_cbor(j)))
+        {
+            CHECK(!element.is_number_unsigned());
+        }
+
+        // CBOR unsigned integer 2^64-1 does not fit and is read as float
+        const std::vector<std::uint8_t> cbor_max = {0x1B, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
+        const Json from_cbor = Json::from_cbor(cbor_max);
+        CHECK(from_cbor.is_number_float());
+        CHECK(from_cbor.template get<double>() == 18446744073709551615.0);
+
+        // MessagePack uint 8 is read as number_integer
+        const std::vector<std::uint8_t> msgpack_uint8 = {0xCC, 0xC8};
+        const Json from_msgpack = Json::from_msgpack(msgpack_uint8);
+        CHECK(from_msgpack.is_number_integer());
+        CHECK(from_msgpack == 200);
+    }
+}
+
+TEST_CASE("same type for number_integer_t and number_unsigned_t: type traits")
+{
+    CHECK(std::is_same<nlohmann::detail::number_unsigned_overload_t<json64>, nlohmann::detail::same_as_number_integer_type>::value);
+    CHECK(std::is_same<nlohmann::detail::number_unsigned_overload_t<nlohmann::json>, std::uint64_t>::value);
+    CHECK(nlohmann::detail::is_compatible_number_integer_type<json64, unsigned>::value);
+    CHECK(!nlohmann::detail::is_compatible_number_integer_type<nlohmann::json, unsigned>::value);
+    CHECK(!nlohmann::detail::is_compatible_number_integer_type<json64, bool>::value);
+}
@@ -20,8 +20,11 @@
 using nlohmann::json;

 #include <array>
+#include <cstdint>
 #include <sstream>
 #include <iomanip>
+#include <string>
+#include <vector>

 #include "test_utils.hpp"

@@ -923,66 +926,68 @@ TEST_CASE("serialization boundary values for the string buffer")
    // mid-string once fewer than 13 bytes remain (`string_buffer.size() - bytes
    // < 13`), 13 being one more than the most a single code point can ever
    // write at once (a surrogate pair: two back-to-back "\uXXXX" escapes, 12
-    // bytes). Every write into string_buffer that this check protects happens
-    // in steps of 2 (a simple "\\x" escape) or 6 (one "\uXXXX" unit), so
-    // `bytes` only ever takes even values at the point the check runs - the
-    // tightest values actually reachable are therefore 498 (512 - 498 == 14,
-    // one simple escape away from the threshold) and 500 (512 - 500 == 12,
-    // where the flush fires immediately and resets bytes to 0).
+    // bytes). Characters below 0x60 (control characters, '"' and '\\') are
+    // escaped straight into the write buffer and never reach string_buffer, so
+    // under ensure_ascii it fills in steps of 6 (one "\uXXXX" unit for a
+    // character below U+10000) or 12 (a surrogate pair). With 2-byte characters
+    // such as U+00E4, `bytes` takes multiples of 6 at the point the check runs;
+    // the tightest values reachable are therefore 498 (512 - 498 == 14, after
+    // 83 characters) and 504 (512 - 504 == 8, after 84 characters, where the
+    // flush fires immediately and resets bytes to 0).

-    SECTION("a run of 2-byte escapes lands bytes on, and one step past, the flush threshold")
+    SECTION("a run of 6-byte escapes lands bytes on, and one step past, the flush threshold")
    {
        for (const int count :
                {
-                    249, 250, 251
+                    83, 84, 85
                })
        {
            CAPTURE(count)
-            const json j = std::string(static_cast<std::size_t>(count), '\n');
+            std::string umlauts;
            std::string expected = "\"";
            for (int i = 0; i < count; ++i)
            {
-                expected += "\\n";
+                umlauts += "\xC3\xA4";
+                expected += "\\u00e4";
            }
            expected += '"';
-            CHECK(j.dump() == expected);
+            CHECK(json(umlauts).dump(-1, ' ', true) == expected);
        }
    }

-    SECTION("an ASCII prefix leaves the tightest reachable margin before a 12-byte surrogate pair")
+    SECTION("a prefix leaves the tightest reachable margin before a 12-byte surrogate pair")
    {
        // U+1F600 (the "\xF0\x9F\x98\x80" UTF-8 bytes) is dumped under
        // ensure_ascii as the 12-byte surrogate pair "\ud83d\ude00"; that
        // write happens in a single step with no intermediate flush check, so
        // it is the write most exposed by an off-by-one in the "< 13" guard.
-        // A prefix of 249 newlines leaves exactly 14 bytes of headroom
+        // A prefix of 83 U+00E4 characters leaves exactly 14 bytes of headroom
        // (512 - 498), the smallest margin the guard ever actually allows
-        // into a new code point; 250 newlines instead trigger the guard's own
+        // into a new code point; 84 characters instead trigger the guard's own
        // flush first, so the emoji starts from a freshly emptied (512-byte)
-        // buffer, and 251 repeats that with one more escape already past the
+        // buffer, and 85 repeats that with one more escape already past the
        // reset. Together they cover the margin the guard allows landing on,
        // one step before, and one step after - all must still produce the
        // identical, correct escapes.
        for (const int prefix_count :
                {
-                    249, 250, 251
+                    83, 84, 85
                })
        {
            CAPTURE(prefix_count)
-            const std::string prefix(static_cast<std::size_t>(prefix_count), '\n');
-            const std::string emoji = "\xF0\x9F\x98\x80";
-            const json j = prefix + emoji;
-
+            std::string prefix;
            std::string expected_prefix;
            for (int i = 0; i < prefix_count; ++i)
            {
-                expected_prefix += "\\n";
+                prefix += "\xC3\xA4";
+                expected_prefix += "\\u00e4";
            }
+            const std::string emoji = "\xF0\x9F\x98\x80";
+            const json j = prefix + emoji;

-            // newline escaping does not depend on ensure_ascii: only the
-            // emoji differs (raw UTF-8 bytes vs. a \u-escaped surrogate pair)
+            // without ensure_ascii, the whole string is copied unchanged
            std::string expected_raw = "\"";
-            expected_raw += expected_prefix;
+            expected_raw += prefix;
            expected_raw += emoji;
            expected_raw += '"';
            std::string expected_ascii = "\"";
@@ -1027,3 +1032,524 @@ TEST_CASE("serialization boundary values for the string buffer")
        }
    }
 }
+
+namespace
+{
+// appends the escaped form of the ASCII character c to out; written
+// independently of the table in serializer::ascii_escapes()
+void append_escaped_ascii(std::string& out, const char c, const bool ensure_ascii)
+{
+    const auto byte = static_cast<unsigned char>(c);
+    switch (byte)
+    {
+        case '\b':
+            out += "\\b";
+            break;
+        case '\t':
+            out += "\\t";
+            break;
+        case '\n':
+            out += "\\n";
+            break;
+        case '\f':
+            out += "\\f";
+            break;
+        case '\r':
+            out += "\\r";
+            break;
+        case '"':
+            out += "\\\"";
+            break;
+        case '\\':
+            out += "\\\\";
+            break;
+        default:
+            if (byte < 0x20 || (ensure_ascii && byte == 0x7F))
+            {
+                // byte < 0x80, so the first two hex digits are 0
+                const char* const hex = "0123456789abcdef";
+                out += "\\u00";
+                out += hex[byte >> 4U];
+                out += hex[byte & 0x0FU];
+            }
+            else
+            {
+                out += c;
+            }
+            break;
+    }
+}
+
+// reference escaper for ASCII strings
+std::string reference_escape_ascii(const std::string& s, const bool ensure_ascii)
+{
+    std::string result = "\"";
+    for (const char c : s)
+    {
+        append_escaped_ascii(result, c, ensure_ascii);
+    }
+    result += '"';
+    return result;
+}
+} // namespace
+
+TEST_CASE("characters below 0x60 are escaped from a table straight into the write buffer")
+{
+    SECTION("every ASCII character at every position")
+    {
+        // lengths up to 17 cover the 8-byte strides of the bulk scanner on
+        // both sides of the character, so the scanner stops at it from every
+        // offset
+        for (std::size_t length = 1; length <= 17; ++length)
+        {
+            for (std::size_t pos = 0; pos < length; ++pos)
+            {
+                for (unsigned int c = 0; c < 0x80; ++c)
+                {
+                    std::string s(length, 'a');
+                    s[pos] = static_cast<char>(c);
+                    CAPTURE(length)
+                    CAPTURE(pos)
+                    CAPTURE(c)
+                    const json j = s;
+                    CHECK(j.dump(-1, ' ', false) == reference_escape_ascii(s, false));
+                    CHECK(j.dump(-1, ' ', true) == reference_escape_ascii(s, true));
+                }
+            }
+        }
+    }
+
+    SECTION("runs of escaped characters")
+    {
+        std::string s;
+        for (unsigned int c = 0; c < 0x20; ++c)
+        {
+            s += static_cast<char>(c);
+        }
+        s += R"("\"\)";
+        CHECK(json(s).dump() == reference_escape_ascii(s, false));
+        CHECK(json(s).dump(-1, ' ', true) == reference_escape_ascii(s, true));
+    }
+
+    SECTION("escapes straddle the end of the write buffer")
+    {
+        // the 8-byte store of a table entry needs room for all 8 bytes, even
+        // when the escape itself is shorter; a prefix of k plain characters
+        // shifts the 6-byte escapes across every offset of the 1024-byte
+        // write buffer
+        for (std::size_t k = 0; k < 8; ++k)
+        {
+            CAPTURE(k)
+            const std::string s = std::string(k, 'a') + std::string(400, '\x01');
+            CHECK(json(s).dump() == reference_escape_ascii(s, false));
+            CHECK(json::array({s, s}).dump() == "[" + reference_escape_ascii(s, false) + "," + reference_escape_ascii(s, false) + "]");
+        }
+    }
+
+    SECTION("pending \\u escapes of non-ASCII characters are written first")
+    {
+        // under ensure_ascii, U+00E4 is \u-escaped into the string buffer;
+        // a following escape from the table must not overtake it
+        const json j = "\xC3\xA4\n\xC3\xA4\"\xF0\x9F\x98\x80\\";
+        CHECK(j.dump(-1, ' ', true) == "\"\\u00e4\\n\\u00e4\\\"\\ud83d\\ude00\\\\\"");
+        CHECK(j.dump(-1, ' ', false) == "\"\xC3\xA4\\n\xC3\xA4\\\"\xF0\x9F\x98\x80\\\\\"");
+    }
+
+    SECTION("escapes after invalid UTF-8 for every error handler")
+    {
+        const json j = "a\xFF\n\xC3\"";
+        CHECK_THROWS_WITH_AS(utils::ignore_return_value(j.dump()), "[json.exception.type_error.316] invalid UTF-8 byte at index 1: 0xFF", json::type_error&);
+        CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"a\\n\\\"\"");
+        CHECK(j.dump(-1, ' ', true, json::error_handler_t::ignore) == "\"a\\n\\\"\"");
+        CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"a\xEF\xBF\xBD\\n\xEF\xBF\xBD\\\"\"");
+        CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"a\\ufffd\\n\\ufffd\\\"\"");
+        CHECK(j.dump(-1, ' ', false, json::error_handler_t::keep) == "\"a\xFF\\n\xC3\\\"\"");
+        CHECK(j.dump(-1, ' ', true, json::error_handler_t::keep) == "\"a\xFF\\n\xC3\\\"\"");
+    }
+}
+
+namespace
+{
+// expected result of dumping a string: the output, or (with
+// error_handler_t::strict) the message of the type_error.316 exception
+struct expected_dump
+{
+    bool throws = false;
+    std::string text{}; // NOLINT(readability-redundant-member-init)
+};
+
+std::string upper_hex_byte(const unsigned char byte)
+{
+    const char* const hex = "0123456789ABCDEF";
+    return std::string(1, hex[byte >> 4U]) + hex[byte & 0x0FU];
+}
+
+void append_u_escape(std::string& out, const std::uint32_t code_unit)
+{
+    const char* const hex = "0123456789abcdef";
+    out += "\\u";
+    for (int shift = 12; shift >= 0; shift -= 4)
+    {
+        out += hex[(code_unit >> static_cast<unsigned int>(shift)) & 0x0FU];
+    }
+}
+
+void append_replacement_character(std::string& out, const bool ensure_ascii)
+{
+    out += ensure_ascii ? "\\ufffd" : "\xEF\xBF\xBD";
+}
+
+// reference serializer for arbitrary byte strings, written from the documented
+// behavior of dump() and independently of serializer::dump_escaped(): UTF-8 is
+// decoded strictly (well-formed sequences as in Table 3-7 of the Unicode
+// Standard), and each ill-formed sequence is handled as the error handler says
+expected_dump reference_dump_string(const std::string& s, const bool ensure_ascii, const json::error_handler_t error_handler)
+{
+    expected_dump result;
+    std::string& out = result.text;
+    out = "\"";
+
+    // handle the ill-formed bytes s[begin, end), of which s[index] is the byte
+    // that could not be decoded; returns false if an exception is expected
+    const auto ill_formed = [&](const std::size_t begin, const std::size_t end, const std::size_t index)
+    {
+        switch (error_handler)
+        {
+            case json::error_handler_t::strict:
+                result.throws = true;
+                out = "[json.exception.type_error.316] invalid UTF-8 byte at index " + std::to_string(index) + ": 0x" + upper_hex_byte(static_cast<unsigned char>(s[index]));
+                return false;
+            case json::error_handler_t::ignore:
+                break;
+            case json::error_handler_t::replace:
+                append_replacement_character(out, ensure_ascii);
+                break;
+            case json::error_handler_t::keep:
+            default:
+                // kept as is, even with ensure_ascii
+                out.append(s, begin, end - begin);
+                break;
+        }
+        return true;
+    };
+
+    std::size_t i = 0;
+    while (i < s.size())
+    {
+        const auto lead = static_cast<unsigned char>(s[i]);
+        if (lead < 0x80)
+        {
+            append_escaped_ascii(out, s[i], ensure_ascii);
+            ++i;
+            continue;
+        }
+
+        // number of bytes of the sequence and the range of its second byte
+        std::size_t length = 0;
+        std::uint32_t code_point = 0;
+        unsigned char lower = 0x80;
+        unsigned char upper = 0xBF;
+        if (lead >= 0xC2 && lead <= 0xDF)
+        {
+            length = 2;
+            code_point = lead & 0x1FU;
+        }
+        else if (lead >= 0xE0 && lead <= 0xEF)
+        {
+            length = 3;
+            code_point = lead & 0x0FU;
+            lower = (lead == 0xE0) ? 0xA0 : 0x80; // no overlong encodings
+            upper = (lead == 0xED) ? 0x9F : 0xBF; // no surrogates
+        }
+        else if (lead >= 0xF0 && lead <= 0xF4)
+        {
+            length = 4;
+            code_point = lead & 0x07U;
+            lower = (lead == 0xF0) ? 0x90 : 0x80; // no overlong encodings
+            upper = (lead == 0xF4) ? 0x8F : 0xBF; // nothing above U+10FFFF
+        }
+        else
+        {
+            // a byte that cannot start a sequence is consumed
+            if (!ill_formed(i, i + 1, i))
+            {
+                return result;
+            }
+            ++i;
+            continue;
+        }
+
+        std::size_t j = i + 1;
+        for (; j < i + length; ++j)
+        {
+            if (j == s.size())
+            {
+                // the string ends in the middle of the sequence
+                switch (error_handler)
+                {
+                    case json::error_handler_t::strict:
+                        result.throws = true;
+                        out = "[json.exception.type_error.316] incomplete UTF-8 string; last byte: 0x" + upper_hex_byte(static_cast<unsigned char>(s.back()));
+                        return result;
+                    case json::error_handler_t::ignore:
+                        break;
+                    case json::error_handler_t::replace:
+                        append_replacement_character(out, ensure_ascii);
+                        break;
+                    case json::error_handler_t::keep:
+                    default:
+                        out.append(s, i, s.size() - i);
+                        break;
+                }
+                out += '"';
+                return result;
+            }
+
+            const auto byte = static_cast<unsigned char>(s[j]);
+            if (byte < lower || byte > upper)
+            {
+                break;
+            }
+            code_point = (code_point << 6U) | (byte & 0x3FU);
+            lower = 0x80;
+            upper = 0xBF;
+        }
+
+        if (j < i + length)
+        {
+            // the sequence was abandoned at s[j]; that byte is read again as
+            // the start of a new character
+            if (!ill_formed(i, j, j))
+            {
+                return result;
+            }
+            i = j;
+            continue;
+        }
+
+        if (!ensure_ascii)
+        {
+            out.append(s, i, length);
+        }
+        else if (code_point <= 0xFFFF)
+        {
+            append_u_escape(out, code_point);
+        }
+        else
+        {
+            append_u_escape(out, 0xD800U + ((code_point - 0x10000U) >> 10U));
+            append_u_escape(out, 0xDC00U + ((code_point - 0x10000U) & 0x3FFU));
+        }
+        i = j;
+    }
+
+    out += '"';
+    return result;
+}
+
+std::string hex_dump(const std::string& s)
+{
+    std::string result;
+    for (const char c : s)
+    {
+        result += upper_hex_byte(static_cast<unsigned char>(c));
+        result += ' ';
+    }
+    return result;
+}
+
+// compares dump() of s with the reference for every error handler, with
+// ensure_ascii on and off; CHECKs only on a mismatch to keep the sweep fast;
+// error_handler_t::strict can be skipped where the position of the string
+// buffer does not matter, as throwing is slow on some platforms
+void check_dump_against_reference(const std::string& s, const bool with_strict = true)
+{
+    const json j = s;
+    const std::array<json::error_handler_t, 4> error_handlers =
+    {
+        {
+            json::error_handler_t::strict, json::error_handler_t::ignore,
+            json::error_handler_t::replace, json::error_handler_t::keep
+        }
+    };
+    for (const auto error_handler : error_handlers)
+    {
+        if (!with_strict && error_handler == json::error_handler_t::strict)
+        {
+            continue;
+        }
+        for (const bool ensure_ascii :
+                {
+                    false, true
+                })
+        {
+            const expected_dump expected = reference_dump_string(s, ensure_ascii, error_handler);
+            expected_dump actual;
+            int id = 0;
+            try
+            {
+                actual.text = j.dump(-1, ' ', ensure_ascii, error_handler);
+            }
+            catch (const json::exception& e)
+            {
+                actual.throws = true;
+                actual.text = e.what();
+                id = e.id;
+            }
+            if (actual.throws != expected.throws || actual.text != expected.text || (actual.throws && id != 316))
+            {
+                const std::string input = hex_dump(s);
+                CAPTURE(input)
+                CAPTURE(ensure_ascii)
+                CAPTURE(static_cast<int>(error_handler))
+                CHECK(actual.throws == expected.throws);
+                CHECK(actual.text == expected.text);
+                CHECK((!actual.throws || id == 316));
+            }
+        }
+    }
+}
+} // namespace
+
+TEST_CASE("invalid UTF-8 at every position is handled like the reference")
+{
+    // ill-formed byte sequences; those that end in a truncated sequence are
+    // also cut short by the filler that follows, or by the end of the string
+    const std::vector<std::string> patterns =
+    {
+        // stray continuation bytes
+        "\x80", "\xBF",
+        // bytes that cannot start a sequence
+        "\xC0", "\xC1", "\xF5", "\xF6", "\xF7", "\xF8", "\xF9", "\xFA", "\xFB", "\xFC", "\xFD", "\xFE", "\xFF",
+        // overlong encodings
+        "\xC0\xAF", "\xE0\x80\x80", "\xF0\x80\x80\x80",
+        // UTF-16 surrogates
+        "\xED\xA0\x80", "\xED\xBF\xBF",
+        // a code point above U+10FFFF
+        "\xF4\x90\x80\x80",
+        // sequences cut short by ASCII, a control character, a quote, a
+        // backslash, DEL, or the lead byte of a well-formed character
+        "\xC3" "a", "\xE2\x82" "\n", "\xE2\x82\"", "\xF0\x9F\x98\\", "\xC3\x7F", "\xC3\xC3\xA4", "\xE2\xF0\x9F\x98\x80",
+        // truncated sequences
+        "\xC3", "\xE2\x82", "\xF0\x9F\x98"
+    };
+
+    // well-formed characters of 1, 2, 3, and 4 bytes
+    const std::vector<std::string> fillers = {"a", "\xC3\xA4", "\xE2\x82\xAC", "\xF0\x9F\x98\x80"};
+
+    const auto make_string = [](const std::string & filler, const std::size_t before, const std::string & pattern, const std::size_t after)
+    {
+        std::string s;
+        for (std::size_t k = 0; k < before; ++k)
+        {
+            s += filler;
+        }
+        s += pattern;
+        for (std::size_t k = 0; k < after; ++k)
+        {
+            s += filler;
+        }
+        return s;
+    };
+
+    SECTION("the reference")
+    {
+        // the reference itself, against hand-written results
+        const std::string s = "a\xFF\n\xC3\"\xE0\x80\xF0\x9F\x98\x80\xE2\x82";
+        CHECK(reference_dump_string(s, false, json::error_handler_t::strict).text == "[json.exception.type_error.316] invalid UTF-8 byte at index 1: 0xFF");
+        CHECK(reference_dump_string(s.substr(2), false, json::error_handler_t::strict).text == "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0x22");
+        CHECK(reference_dump_string("\xF0\x9F\x98\x80\xE2\x82", true, json::error_handler_t::strict).text == "[json.exception.type_error.316] incomplete UTF-8 string; last byte: 0x82");
+        CHECK(reference_dump_string(s, false, json::error_handler_t::ignore).text == "\"a\\n\\\"\xF0\x9F\x98\x80\"");
+        CHECK(reference_dump_string(s, true, json::error_handler_t::ignore).text == "\"a\\n\\\"\\ud83d\\ude00\"");
+        CHECK(reference_dump_string(s, false, json::error_handler_t::replace).text == "\"a\xEF\xBF\xBD\\n\xEF\xBF\xBD\\\"\xEF\xBF\xBD\xEF\xBF\xBD\xF0\x9F\x98\x80\xEF\xBF\xBD\"");
+        CHECK(reference_dump_string(s, true, json::error_handler_t::replace).text == "\"a\\ufffd\\n\\ufffd\\\"\\ufffd\\ufffd\\ud83d\\ude00\\ufffd\"");
+        CHECK(reference_dump_string(s, false, json::error_handler_t::keep).text == "\"" + std::string("a\xFF\\n\xC3\\\"\xE0\x80\xF0\x9F\x98\x80\xE2\x82") + "\"");
+        CHECK(reference_dump_string(s, true, json::error_handler_t::keep).text == "\"" + std::string("a\xFF\\n\xC3\\\"\xE0\x80\\ud83d\\ude00\xE2\x82") + "\"");
+        check_dump_against_reference(s);
+    }
+
+    SECTION("short strings")
+    {
+        // strings of up to 17 bytes put the pattern at every offset of an
+        // 8-byte stride of the bulk scanners, with whole strides on both
+        // sides; lengths around 24, 32, and 40 bytes cross the 16- and 32-byte
+        // strides; error_handler_t::strict is checked for up to 17 bytes of
+        // ASCII and 8 bytes of other characters only, as throwing is slow on
+        // some platforms
+        for (const auto& filler : fillers)
+        {
+            for (std::size_t length = 0; length * filler.size() <= 40; ++length)
+            {
+                const std::size_t bytes = length * filler.size();
+                if (filler.size() == 1 && bytes > 17 && (bytes + 1) % 8 > 2)
+                {
+                    continue;
+                }
+                for (std::size_t pos = 0; pos <= length; ++pos)
+                {
+                    for (const auto& pattern : patterns)
+                    {
+                        check_dump_against_reference(make_string(filler, pos, pattern, length - pos), bytes <= (filler.size() == 1 ? 17 : 8));
+                    }
+                }
+            }
+        }
+    }
+
+    SECTION("strings crossing the end of the string buffer")
+    {
+        // characters that are not copied in bulk go through a 512-byte string
+        // buffer that is written out once fewer than 13 bytes are left; with
+        // ensure_ascii, each 2-byte character takes 6 bytes of it and each
+        // 4-byte character 12, so the pattern meets the end of the buffer after
+        // about 84 or 42 characters (3-byte characters behave like 2-byte
+        // ones); plain ASCII, copied in bulk, is checked around 512 bytes;
+        // positions further away are sampled; error_handler_t::strict throws
+        // at the first ill-formed byte, regardless of the string buffer, and is
+        // covered above
+        for (const auto& filler : fillers)
+        {
+            if (filler.size() == 3)
+            {
+                continue;
+            }
+            const std::size_t escaped_size = filler.size() == 1 ? 1 : filler.size() * 3;
+            const std::size_t middle = 506 / escaped_size;
+            const std::size_t window = filler.size() == 1 ? 8 : 16;
+            for (std::size_t pos = 0; pos <= middle + window; pos += (pos + window >= middle) ? 1 : 29)
+            {
+                for (const std::size_t after :
+                        {
+                            std::size_t{0}, std::size_t{12}
+                        })
+                {
+                    for (const auto& pattern : patterns)
+                    {
+                        check_dump_against_reference(make_string(filler, pos, pattern, after), false);
+                    }
+                }
+            }
+        }
+    }
+
+    SECTION("repeated invalid sequences at every offset of the string buffer")
+    {
+        // ill-formed sequences that are kept or replaced fill the string
+        // buffer without a bulk copy in between; a prefix of 0 to 12 bytes
+        // 0xFF (kept as 1 byte, replaced by 3 or 6) shifts them across every
+        // offset of the end of the buffer
+        for (const auto& pattern : patterns)
+        {
+            for (std::size_t shift = 0; shift <= 12; ++shift)
+            {
+                std::string s(shift, '\xFF');
+                while (s.size() < 600)
+                {
+                    s += pattern;
+                }
+                check_dump_against_reference(s, shift == 0);
+                check_dump_against_reference(s + "\xF0\x9F\x98\x80", false);
+            }
+        }
+    }
+}
@@ -0,0 +1,135 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <string>
+
+// The exceptions in hot core functions are constructed out of line. These tests pin the
+// exact what() texts of the sites that moved, so the refactoring cannot change them.
+
+#define CHECK_MSG(expr, msg) CHECK_THROWS_WITH(expr, msg)
+
+TEST_CASE("exception messages of out-of-line throw sites")
+{
+    json arr = {1, 2, 3};
+    json arr2 = {4, 5};
+    json obj = {{"a", 1}, {"b", 2}};
+    json obj2 = {{"c", 3}};
+    json num = 1;
+
+    SECTION("iterators")
+    {
+        CHECK_MSG((void)(arr.begin() == arr2.begin()), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers");
+        CHECK_MSG((void)(arr.begin() < arr2.begin()), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers");
+        CHECK_MSG((void)(obj.begin() < obj.end()), "[json.exception.invalid_iterator.213] cannot compare order of object iterators");
+        CHECK_MSG(obj.begin() += 1, "[json.exception.invalid_iterator.209] cannot use offsets with object iterators");
+        CHECK_MSG((void)(obj.begin() - 1), "[json.exception.invalid_iterator.209] cannot use offsets with object iterators");
+        CHECK_MSG((void)obj.begin()[0], "[json.exception.invalid_iterator.208] cannot use operator[] for object iterators");
+        CHECK_MSG((void)arr.begin().key(), "[json.exception.invalid_iterator.207] cannot use key() for non-object iterators");
+        json null;
+        CHECK_MSG((void)*null.end(), "[json.exception.invalid_iterator.214] cannot get value");
+    }
+
+    SECTION("constructors")
+    {
+        CHECK_MSG(json(arr.begin(), arr2.end()), "[json.exception.invalid_iterator.201] iterators are not compatible");
+        CHECK_MSG(json(num.begin() + 1, num.end() + 1), "[json.exception.invalid_iterator.204] iterators out of range");
+        CHECK_MSG(json(json::initializer_list_t{1, 2}, false, json::value_t::object), "[json.exception.type_error.301] cannot create object from initializer list");
+    }
+
+    SECTION("get_ref and operator[]")
+    {
+        CHECK_MSG((void)num.get_ref<std::string&>(), "[json.exception.type_error.303] incompatible ReferenceType for get_ref, actual type is number");
+        CHECK_MSG((void)num[0], "[json.exception.type_error.305] cannot use operator[] with a numeric argument with number");
+    }
+
+    SECTION("at")
+    {
+        const json carr = arr;
+        const json cobj = obj;
+        CHECK_MSG((void)arr.at(static_cast<json::size_type>(10)), "[json.exception.out_of_range.401] array index 10 is out of range");
+        CHECK_MSG((void)carr.at(static_cast<json::size_type>(3)), "[json.exception.out_of_range.401] array index 3 is out of range");
+        CHECK_MSG((void)num.at(static_cast<json::size_type>(0)), "[json.exception.type_error.304] cannot use at() with number");
+        CHECK_MSG((void)obj.at("z"), "[json.exception.out_of_range.403] key 'z' not found");
+        CHECK_MSG((void)cobj.at("z"), "[json.exception.out_of_range.403] key 'z' not found");
+        CHECK_MSG((void)obj.at(std::string("zz")), "[json.exception.out_of_range.403] key 'zz' not found");
+        CHECK_MSG((void)num.at("a"), "[json.exception.type_error.304] cannot use at() with number");
+
+        nlohmann::ordered_json oobj = {{"a", 1}};
+        const nlohmann::ordered_json coobj = oobj;
+        CHECK_MSG((void)oobj.at("z"), "[json.exception.out_of_range.403] key 'z' not found");
+        CHECK_MSG((void)coobj.at("z"), "[json.exception.out_of_range.403] key 'z' not found");
+        CHECK_MSG((void)coobj.at(std::string("zz")), "[json.exception.out_of_range.403] key 'zz' not found");
+    }
+
+    SECTION("erase")
+    {
+        CHECK_MSG(arr.erase(arr2.begin()), "[json.exception.invalid_iterator.202] iterator does not fit current value");
+        CHECK_MSG(num.erase(num.end()), "[json.exception.invalid_iterator.205] iterator out of range");
+        CHECK_MSG(arr.erase(arr.begin(), arr2.end()), "[json.exception.invalid_iterator.203] iterators do not fit current value");
+        CHECK_MSG(num.erase(num.begin() + 1, num.end()), "[json.exception.invalid_iterator.204] iterators out of range");
+        CHECK_MSG(arr.erase(static_cast<json::size_type>(10)), "[json.exception.out_of_range.401] array index 10 is out of range");
+    }
+
+    SECTION("insert")
+    {
+        CHECK_MSG(arr.insert(arr2.begin(), 1), "[json.exception.invalid_iterator.202] iterator does not fit current value");
+        CHECK_MSG(arr.insert(arr2.begin(), 2, 1), "[json.exception.invalid_iterator.202] iterator does not fit current value");
+        CHECK_MSG(arr.insert(arr2.begin(), arr2.begin(), arr2.end()), "[json.exception.invalid_iterator.202] iterator does not fit current value");
+        CHECK_MSG(arr.insert(arr.begin(), arr.begin(), arr2.end()), "[json.exception.invalid_iterator.210] iterators do not fit");
+        CHECK_MSG(arr.insert(arr.begin(), arr.begin(), arr.end()), "[json.exception.invalid_iterator.211] passed iterators may not belong to container");
+        CHECK_MSG(arr.insert(arr.begin(), obj.begin(), obj.end()), "[json.exception.invalid_iterator.202] iterators first and last must point to arrays");
+        CHECK_MSG(arr.insert(arr2.begin(), {1, 2}), "[json.exception.invalid_iterator.202] iterator does not fit current value");
+        CHECK_MSG(obj.insert(obj2.begin(), arr.end()), "[json.exception.invalid_iterator.210] iterators do not fit");
+        CHECK_MSG(obj.insert(arr.begin(), arr.end()), "[json.exception.invalid_iterator.202] iterators first and last must point to objects");
+        CHECK_MSG(obj.update(arr.begin(), arr2.end()), "[json.exception.invalid_iterator.210] iterators do not fit");
+    }
+
+    SECTION("patch")
+    {
+        const auto patch_msg = [](const char* doc, const char* patch)
+        {
+            try
+            {
+                json d = json::parse(doc);
+                d.patch(json::parse(patch));
+            }
+            catch (const json::exception& e)
+            {
+                // with JSON_DIAGNOSTICS, what() names the offending value like "(/0) "; drop it
+                std::string msg = e.what();
+                const auto pos = msg.find(" (/");
+                if (pos != std::string::npos)
+                {
+                    msg.erase(pos + 1, msg.find(") ", pos) - pos + 1);
+                }
+                return msg;
+            }
+            return std::string();
+        };
+
+        CHECK(patch_msg("{}", "{}") == "[json.exception.parse_error.104] parse error: JSON patch must be an array of objects");
+        CHECK(patch_msg("{}", "[1]") == "[json.exception.parse_error.104] parse error: JSON patch must be an array of objects");
+        CHECK(patch_msg("{}", "[{}]") == "[json.exception.parse_error.105] parse error: operation must have member 'op'");
+        CHECK(patch_msg("{}", "[{\"op\":1}]") == "[json.exception.parse_error.105] parse error: operation must have string member 'op'");
+        CHECK(patch_msg("{}", "[{\"op\":\"add\"}]") == "[json.exception.parse_error.105] parse error: operation 'add' must have member 'path'");
+        CHECK(patch_msg("{}", "[{\"op\":\"add\",\"path\":1}]") == "[json.exception.parse_error.105] parse error: operation 'add' must have string member 'path'");
+        CHECK(patch_msg("{}", "[{\"op\":\"foo\",\"path\":\"\"}]") == "[json.exception.parse_error.105] parse error: operation value 'foo' is invalid");
+        CHECK(patch_msg("{\"a\":1}", "[{\"op\":\"remove\",\"path\":\"/b\"}]") == "[json.exception.out_of_range.403] key 'b' not found");
+        CHECK(patch_msg("[1]", "[{\"op\":\"add\",\"path\":\"/5\",\"value\":0}]") == "[json.exception.out_of_range.401] array index 5 is out of range");
+        CHECK(patch_msg("{\"a\":1}", "[{\"op\":\"add\",\"path\":\"/a/b\",\"value\":0}]") == "[json.exception.out_of_range.411] cannot add value: the JSON Patch 'add' target's parent is of type number, but must be an object or array");
+        CHECK(patch_msg("{\"a\":1}", "[{\"op\":\"remove\",\"path\":\"/a/b\"}]") == "[json.exception.out_of_range.413] cannot remove value: the JSON Patch 'remove' target's parent is of type number, but must be an object or array");
+        CHECK(patch_msg("{\"a\":{}}", "[{\"op\":\"move\",\"from\":\"/a\",\"path\":\"/a/b\"}]") == "[json.exception.out_of_range.414] cannot move value: 'from' path '/a' is a proper prefix of 'path' '/a/b'");
+        CHECK(patch_msg("{\"a\":1}", "[{\"op\":\"test\",\"path\":\"/a\",\"value\":2}]") == "[json.exception.other_error.501] unsuccessful: {\"op\":\"test\",\"path\":\"/a\",\"value\":2}");
+        CHECK(patch_msg("{\"a\":1}", "[{\"op\":\"move\",\"path\":\"/a\"}]") == "[json.exception.parse_error.105] parse error: operation 'move' must have member 'from'");
+    }
+}
@@ -21,11 +21,8 @@ using nlohmann::detail::dtoa_impl::reinterpret_bits;
 #include <cstdint>
 #include <cstdio>
 #include <cstdlib>
-#include <iomanip>
 #include <limits>
-#include <locale>
 #include <random>
-#include <sstream>
 #include <string>
 #include <utility>
 #include <vector>
@@ -689,20 +686,13 @@ void check_shortest(double v)
    const std::string& digits = de.first;
    if (digits.size() > 1)
    {
-        // the decimals of one digit fewer next to the value
-        // (a stream rather than snprintf("%.*e"), whose output GCC cannot bound)
-        std::ostringstream shorter;
-        shorter.imbue(std::locale::classic());
-        shorter << std::scientific << std::setprecision(static_cast<int>(digits.size()) - 2) << v;
-        const auto near = digits_and_exponent(shorter.str());
-        // as an integer with digits.size() - 1 digits
-        std::string m = near.first;
-        int e = near.second;
-        while (m.size() < digits.size() - 1)
-        {
-            m += '0';
-            --e;
-        }
+        // the decimals of one digit fewer next to the value: v lies within
+        // half a unit of the last digit of text, so the closest ones are the
+        // truncated digits and their successor
+        // (not a stream with std::setprecision(digits.size() - 2): the
+        // standard library of MSVC 2017 ignores a precision of 0)
+        const std::string m = digits.substr(0, digits.size() - 1);
+        const int e = de.second + 1;
        const std::uint64_t mid = std::stoull(m);
        for (const std::uint64_t candidate :
                {
@@ -0,0 +1,257 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <array>
+#include <deque>
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <string>
+#include <unordered_map>
+#include <utility>
+#include <valarray>
+#include <vector>
+
+#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1)
+    #if __has_include(<filesystem>)
+        #include <filesystem>
+        #define TO_JSON_RVALUE_HAS_FS 1
+    #endif
+#endif
+
+namespace
+{
+// element type that counts how it is converted to JSON: a conversion from an
+// lvalue copies, a conversion from an rvalue moves
+struct tracked
+{
+    std::string payload;
+    bool moved_from = false;
+
+    explicit tracked(std::string p) : payload(std::move(p)) {}
+    tracked(const tracked&) = default;
+    tracked& operator=(const tracked&) = default;
+    tracked(tracked&& other) noexcept : payload(std::move(other.payload)), moved_from(other.moved_from)
+    {
+        other.moved_from = true;
+    }
+    tracked& operator=(tracked&& other) noexcept
+    {
+        payload = std::move(other.payload);
+        moved_from = other.moved_from;
+        other.moved_from = true;
+        return *this;
+    }
+    ~tracked() = default;
+};
+
+int tracked_copies = 0; // NOLINT(cppcoreguidelines-avoid-non-const-global-variables,misc-use-internal-linkage)
+int tracked_moves = 0;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables,misc-use-internal-linkage)
+
+void to_json(json& j, const tracked& t)
+{
+    ++tracked_copies;
+    j = t.payload;
+}
+
+void to_json(json& j, tracked&& t)
+{
+    ++tracked_moves;
+    j = std::move(t.payload);
+    t.moved_from = true;
+}
+
+// user type with its own rvalue-aware serializer
+struct udt_container
+{
+    std::vector<int> values;
+};
+} // namespace
+
+namespace nlohmann
+{
+template<>
+struct adl_serializer<udt_container>
+{
+    static void to_json(json& j, const udt_container& c)
+    {
+        j = c.values;
+        j.push_back("copied");
+    }
+    static void to_json(json& j, udt_container&& c)
+    {
+        j = std::move(c.values);
+        j.push_back("moved");
+    }
+};
+} // namespace nlohmann
+
+TEST_CASE("to_json from rvalue containers")
+{
+    const std::string long_a(64, 'a');
+    const std::string long_b(64, 'b');
+
+    SECTION("vector<std::string>: elements are moved")
+    {
+        std::vector<std::string> v{long_a, long_b};
+        const json j = std::move(v);
+        CHECK(j == json::array({long_a, long_b}));
+        for (const auto& s : v) // NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
+        {
+            CHECK(s.empty()); // long strings leave the source element empty when moved
+        }
+    }
+
+    SECTION("vector<std::string>: lvalues are copied and left untouched")
+    {
+        const std::vector<std::string> v{long_a, long_b};
+        const json j = v;
+        CHECK(j == json::array({long_a, long_b}));
+        CHECK(v[0] == long_a);
+        CHECK(v[1] == long_b);
+
+        std::vector<std::string> v2{long_a, long_b};
+        const json j2 = v2;
+        CHECK(j2 == j);
+        CHECK(v2[0] == long_a);
+        CHECK(v2[1] == long_b);
+    }
+
+    SECTION("tracked elements: rvalue moves, lvalue copies")
+    {
+        tracked_copies = 0;
+        tracked_moves = 0;
+
+        std::vector<tracked> v;
+        v.emplace_back("x");
+        v.emplace_back("y");
+
+        const json copy = v;
+        CHECK(copy == json::array({"x", "y"}));
+        CHECK(tracked_copies == 2);
+        CHECK(tracked_moves == 0);
+        CHECK_FALSE(v[0].moved_from);
+
+        const json moved = std::move(v);
+        CHECK(moved == copy);
+        CHECK(tracked_copies == 2);
+        CHECK(tracked_moves == 2);
+    }
+
+    SECTION("const rvalue is copied")
+    {
+        tracked_copies = 0;
+        tracked_moves = 0;
+        const std::vector<tracked> v(2, tracked("z"));
+        const json j = std::move(v); // NOLINT(performance-move-const-arg,hicpp-move-const-arg)
+        CHECK(j == json::array({"z", "z"}));
+        CHECK(tracked_copies == 2);
+        CHECK(tracked_moves == 0);
+    }
+
+    SECTION("other sequence containers")
+    {
+        CHECK(json(std::deque<std::string> {long_a, long_b}) == json::array({long_a, long_b}));
+        CHECK(json(std::list<std::string> {long_a, long_b}) == json::array({long_a, long_b}));
+        CHECK(json(std::forward_list<std::string> {long_a, long_b}) == json::array({long_a, long_b}));
+        CHECK(json(std::array<std::string, 2> {{long_a, long_b}}) == json::array({long_a, long_b}));
+        CHECK(json(std::set<std::string> {long_a, long_b}) == json::array({long_a, long_b}));
+        CHECK(json(std::vector<bool> {true, false}) == json::array({true, false}));
+        CHECK(json(std::vector<int> {1, 2, 3}) == json::array({1, 2, 3}));
+        CHECK(json(std::vector<std::vector<std::string>> {{long_a}, {long_b}}) == json::array({json::array({long_a}), json::array({long_b})}));
+        CHECK(json(std::vector<json> {1, "a"}) == json::array({1, "a"}));
+    }
+
+    SECTION("valarray")
+    {
+        std::valarray<int> va(3);
+        va[0] = 1;
+        va[1] = 2;
+        va[2] = 3;
+        CHECK(json(std::move(va)) == json::array({1, 2, 3})); // NOLINT(performance-move-const-arg,hicpp-move-const-arg)
+        CHECK(json(std::valarray<int>(2)) == json::array({0, 0}));
+    }
+
+    SECTION("array_t and json arrays")
+    {
+        json::array_t arr{1, 2};
+        CHECK(json(std::move(arr)) == json::array({1, 2}));
+        json a = json::array({1, 2});
+        const json b = std::move(a);
+        CHECK(b == json::array({1, 2}));
+    }
+
+    SECTION("object-like containers")
+    {
+        std::map<std::string, std::string> m{{"a", long_a}, {"b", long_b}};
+        const json j = std::move(m);
+        CHECK(j == json({{"a", long_a}, {"b", long_b}}));
+        for (const auto& kv : m) // NOLINT(bugprone-use-after-move,hicpp-invalid-access-moved)
+        {
+            CHECK(kv.second.empty()); // values moved, keys (const) copied
+        }
+
+        const std::map<std::string, std::string> cm{{"a", long_a}};
+        const json jc = cm;
+        CHECK(jc["a"] == long_a);
+        CHECK(cm.at("a") == long_a);
+
+        std::unordered_map<std::string, std::string> um{{"a", long_a}};
+        CHECK(json(std::move(um)) == json({{"a", long_a}}));
+
+        std::multimap<std::string, int> mm{{"a", 1}};
+        CHECK(json(std::move(mm)) == json({{"a", 1}}));
+
+        tracked_copies = 0;
+        tracked_moves = 0;
+        std::map<std::string, tracked> mt;
+        mt.emplace("k", tracked("v"));
+        const json jt = std::move(mt);
+        CHECK(jt == json({{"k", "v"}}));
+        CHECK(tracked_moves == 1);
+        CHECK(tracked_copies == 0);
+
+        json::object_t obj{{"a", 1}};
+        CHECK(json(std::move(obj)) == json({{"a", 1}}));
+    }
+
+    SECTION("user type with its own to_json overloads")
+    {
+        udt_container c{{1, 2}};
+        const json lv = c;
+        CHECK(lv == json::array({1, 2, "copied"}));
+        const json rv = std::move(c);
+        CHECK(rv == json::array({1, 2, "moved"}));
+    }
+
+    SECTION("assignment and implicit conversion")
+    {
+        std::vector<std::string> v{long_a};
+        json j;
+        j = std::move(v);
+        CHECK(j == json::array({long_a}));
+        json k = {std::vector<std::string>{long_b}};
+        CHECK(k.size() == 1);
+    }
+
+#ifdef TO_JSON_RVALUE_HAS_FS
+    SECTION("std::filesystem::path rvalue is still a string")
+    {
+        CHECK(json(std::filesystem::path("a/b")) == json("a/b"));
+#ifdef __cpp_lib_char8_t
+        CHECK(json(std::u8string(u8"a/b")) == json("a/b"));
+#endif
+    }
+#endif
+}