Update ci.yml

Update documentation
Move nontype.hpp to detail
2026-01-19 16:12:15 +00:00 · 2026-01-16 02:16:52 +02:00 · 2025-11-18 14:33:45 +02:00 · 2025-11-18 14:33:45 +02:00 · 2025-11-18 12:06:25 +02:00 · 2025-11-03 18:54:47 +02:00
22 changed files with 3708 additions and 278 deletions
--- a/.drone.jsonnet
+++ b/.drone.jsonnet
@@ -34,7 +34,6 @@ local linux_pipeline(name, image, environment, packages = "", sources = [], arch
                'set -e',
                'uname -a',
                'echo $DRONE_STAGE_MACHINE',
-                'wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -',
            ] +
            (if sources != [] then [ ('apt-add-repository "' + source + '"') for source in sources ] else []) +
            (if packages != "" then [ 'apt-get update', 'apt-get -y install ' + packages ] else []) +
@@ -153,38 +152,31 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
    ),

    linux_pipeline(
-        "Linux 23.04 GCC 13 32/64",
-        "cppalliance/droneubuntu2304:1",
+        "Linux 24.04 GCC 13 32/64",
+        "cppalliance/droneubuntu2404:1",
        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '11,14,17,20,2b', ADDRMD: '32,64' },
        "g++-13-multilib",
    ),

    linux_pipeline(
-        "Linux 24.04 GCC 14 32 ASAN",
+        "Linux 24.04 GCC 14 32/64 ASAN",
        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '32' } + asan,
+        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '32,64' } + asan,
        "g++-14-multilib",
    ),

    linux_pipeline(
-        "Linux 24.04 GCC 14 64 ASAN",
+        "Linux 24.04 GCC 14 32/64 UBSAN",
        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '64' } + asan,
+        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '32,64' } + ubsan,
        "g++-14-multilib",
    ),

    linux_pipeline(
-        "Linux 24.04 GCC 14 32 UBSAN",
-        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '32' } + ubsan,
-        "g++-14-multilib",
-    ),
-
-    linux_pipeline(
-        "Linux 24.04 GCC 14 64 UBSAN",
-        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '64' } + ubsan,
-        "g++-14-multilib",
+        "Linux 25.10 GCC 15 32/64",
+        "cppalliance/droneubuntu2510:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-15', CXXSTD: '11,14,17,20,23,2c', ADDRMD: '32,64' },
+        "g++-15-multilib",
    ),

    linux_pipeline(
@@ -195,38 +187,52 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
    ),

    linux_pipeline(
-        "Linux 23.04 Clang 16",
-        "cppalliance/droneubuntu2304:1",
+        "Linux 24.04 Clang 16",
+        "cppalliance/droneubuntu2404:1",
        { TOOLSET: 'clang', COMPILER: 'clang++-16', CXXSTD: '11,14,17,20,2b' },
        "clang-16",
    ),

    linux_pipeline(
-        "Linux 23.10 Clang 17 UBSAN",
-        "cppalliance/droneubuntu2310:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        "Linux 24.04 Clang 17",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' },
        "clang-17",
    ),

    linux_pipeline(
-        "Linux 23.10 Clang 17 ASAN",
-        "cppalliance/droneubuntu2310:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' } + asan,
-        "clang-17",
-    ),
-
-    linux_pipeline(
-        "Linux 24.04 Clang 18 UBSAN",
+        "Linux 24.04 Clang 18",
        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' },
        "clang-18",
    ),

    linux_pipeline(
-        "Linux 24.04 Clang 18 ASAN",
+        "Linux 24.04 Clang 19",
        "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' } + asan,
-        "clang-18",
+        { TOOLSET: 'clang', COMPILER: 'clang++-19', CXXSTD: '11,14,17,20,2b' },
+        "clang-19",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 Clang 20 UBSAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-20', CXXSTD: '11,14,17,20,23,2c' } + ubsan,
+        "clang-20",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 Clang 20 ASAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-20', CXXSTD: '11,14,17,20,23,2c' } + asan,
+        "clang-20",
+    ),
+
+    linux_pipeline(
+        "Linux 25.10 Clang 21",
+        "cppalliance/droneubuntu2510:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-21', CXXSTD: '11,14,17,20,23,2c' },
+        "clang-21",
    ),

    macos_pipeline(
@@ -251,6 +257,18 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
        xcode_version = "13.4.1", osx_version = "monterey", arch = "arm64",
    ),

+    macos_pipeline(
+        "MacOS 14 Xcode 16.2.0 UBSAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,17,20,2b' } + ubsan,
+        xcode_version = "16.2.0", osx_version = "sonoma", arch = "arm64",
+    ),
+
+    macos_pipeline(
+        "MacOS 14 Xcode 16.2.0 ASAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,17,20,2b' } + asan,
+        xcode_version = "16.2.0", osx_version = "sonoma", arch = "arm64",
+    ),
+
    windows_pipeline(
        "Windows VS2015 msvc-14.0",
        "cppalliance/dronevs2015",
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -39,18 +39,22 @@ jobs:
            install: g++-6
          - toolset: gcc-7
            cxxstd: "03,11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: g++-7
          - toolset: gcc-8
            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: g++-8
          - toolset: gcc-9
            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
          - toolset: gcc-10
            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: g++-10
          - toolset: gcc-11
            cxxstd: "03,11,14,17,2a"
@@ -61,7 +65,7 @@ jobs:
            install: g++-12
          - toolset: gcc-13
            cxxstd: "03,11,14,17,20,2b"
-            container: ubuntu:23.04
+            container: ubuntu:24.04
            os: ubuntu-latest
            install: g++-13
          - toolset: gcc-14
@@ -69,6 +73,11 @@ jobs:
            container: ubuntu:24.04
            os: ubuntu-latest
            install: g++-14
+          - toolset: gcc-15
+            cxxstd: "03,11,14,17,20,23,2c"
+            container: ubuntu:25.04
+            os: ubuntu-latest
+            install: g++-15
          - toolset: clang
            compiler: clang++-3.9
            cxxstd: "03,11,14"
@@ -90,37 +99,44 @@ jobs:
          - toolset: clang
            compiler: clang++-6.0
            cxxstd: "03,11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-6.0
          - toolset: clang
            compiler: clang++-7
            cxxstd: "03,11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-7
          - toolset: clang
            compiler: clang++-8
            cxxstd: "03,11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-8
          - toolset: clang
            compiler: clang++-9
            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-9
          - toolset: clang
            compiler: clang++-10
            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-10
          - toolset: clang
            compiler: clang++-11
            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-11
          - toolset: clang
            compiler: clang++-12
            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
            install: clang-12
          - toolset: clang
            compiler: clang++-13
@@ -143,13 +159,13 @@ jobs:
          - toolset: clang
            compiler: clang++-16
            cxxstd: "03,11,14,17,20,2b"
-            container: ubuntu:23.04
+            container: ubuntu:24.04
            os: ubuntu-latest
            install: clang-16
          - toolset: clang
            compiler: clang++-17
            cxxstd: "03,11,14,17,20,2b"
-            container: ubuntu:23.10
+            container: ubuntu:24.04
            os: ubuntu-latest
            install: clang-17
          - toolset: clang
@@ -159,34 +175,60 @@ jobs:
            os: ubuntu-latest
            install: clang-18
          - toolset: clang
+            compiler: clang++-19
            cxxstd: "03,11,14,17,20,2b"
-            os: macos-12
+            container: ubuntu:24.04
+            os: ubuntu-latest
+            install: clang-19
          - toolset: clang
-            cxxstd: "03,11,14,17,20,2b"
-            os: macos-13
+            compiler: clang++-20
+            cxxstd: "03,11,14,17,20,23,2c"
+            container: ubuntu:24.04
+            os: ubuntu-latest
+            install: clang-20
+          - toolset: clang
+            compiler: clang++-21
+            cxxstd: "03,11,14,17,20,23,2c"
+            container: ubuntu:25.10
+            os: ubuntu-latest
+            install: clang-21
          - toolset: clang
            cxxstd: "03,11,14,17,20,2b"
            os: macos-14
+          - toolset: clang
+            cxxstd: "03,11,14,17,20,23,2c"
+            os: macos-15
+          - toolset: clang
+            cxxstd: "03,11,14,17,20,23,2c"
+            os: macos-26

    runs-on: ${{matrix.os}}
-    container: ${{matrix.container}}
+
+    container:
+      image: ${{matrix.container}}
+      volumes:
+        - /node20217:/node20217:rw,rshared
+        - ${{ startsWith(matrix.container, 'ubuntu:1') && '/node20217:/__e/node20:ro,rshared' || ' ' }}

    defaults:
      run:
        shell: bash

    steps:
-      - name: Enable Node 16
-        run: |
-          echo "ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true" >> $GITHUB_ENV
-
-      - uses: actions/checkout@v3
-
      - name: Setup container environment
        if: matrix.container
        run: |
          apt-get update
-          apt-get -y install sudo python3 git g++
+          apt-get -y install sudo python3 git g++ curl xz-utils
+
+      - name: Install nodejs20glibc2.17
+        if: ${{ startsWith( matrix.container, 'ubuntu:1' ) }}
+        run: |
+          curl -LO https://archives.boost.io/misc/node/node-v20.9.0-linux-x64-glibc-217.tar.xz
+          tar -xf node-v20.9.0-linux-x64-glibc-217.tar.xz --strip-components 1 -C /node20217
+          ldd /__e/node20/bin/node
+
+      - uses: actions/checkout@v4

      - name: Install packages
        if: matrix.install
@@ -232,14 +274,6 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - toolset: msvc-14.0
-            cxxstd: "14,latest"
-            addrmd: 32,64
-            os: windows-2019
-          - toolset: msvc-14.2
-            cxxstd: "14,17,20,latest"
-            addrmd: 32,64
-            os: windows-2019
          - toolset: msvc-14.3
            cxxstd: "14,17,20,latest"
            addrmd: 32,64
@@ -251,7 +285,7 @@ jobs:
          - toolset: gcc
            cxxstd: "03,11,14,17,2a"
            addrmd: 64
-            os: windows-2019
+            os: windows-2022

    runs-on: ${{matrix.os}}

@@ -291,11 +325,11 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: ubuntu-20.04
          - os: ubuntu-22.04
-          - os: macos-12
-          - os: macos-13
+          - os: ubuntu-24.04
          - os: macos-14
+          - os: macos-15
+          - os: macos-26

    runs-on: ${{matrix.os}}

@@ -340,11 +374,11 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: ubuntu-20.04
          - os: ubuntu-22.04
-          - os: macos-12
-          - os: macos-13
+          - os: ubuntu-24.04
          - os: macos-14
+          - os: macos-15
+          - os: macos-26

    runs-on: ${{matrix.os}}

@@ -399,11 +433,11 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: ubuntu-20.04
          - os: ubuntu-22.04
-          - os: macos-12
-          - os: macos-13
+          - os: ubuntu-24.04
          - os: macos-14
+          - os: macos-15
+          - os: macos-26

    runs-on: ${{matrix.os}}

@@ -456,8 +490,7 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest

    runs-on: ${{matrix.os}}

@@ -505,8 +538,7 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest

    runs-on: ${{matrix.os}}

@@ -572,8 +604,7 @@ jobs:
      fail-fast: false
      matrix:
        include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest

    runs-on: ${{matrix.os}}

--- a/doc/compat/changelog.adoc
+++ b/doc/compat/changelog.adoc
@@ -8,6 +8,14 @@ https://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix: changelog_

+## Changes in 1.90.0
+
+* Added `to_underlying.hpp` (contributed by Braden Ganetsky.)
+
+## Changes in 1.89.0
+
+* Added `move_only_function.hpp`.
+
 ## Changes in 1.87.0

 * Added `to_array.hpp` (contributed by Ruben Perez Hidalgo.)
--- a/doc/compat/function_ref.adoc
+++ b/doc/compat/function_ref.adoc
@@ -18,6 +18,8 @@ The header `<boost/compat/function_ref.hpp>` implements the {cpp}26 class
 `function_ref` supports every combination of `const` and `noexcept` and is useful for writing higher-order functions as
 it can avoid a template parameter or an allocation (as `std::function` is known for).

+Since `nontype_t` requires {cpp}17 as it has a template parameter of type `auto`, the constructors taking `nontype_t<f>` are only available under {cpp}17 or later.
+
 ## Example

 ```cpp
@@ -48,19 +50,22 @@ struct function_ref;
 // cv is either `const` or empty
 // noex is either `true` or `false`
 template<class R, class... ArgTypes>
-class function_ref<R(ArgTypes...) cv noexcept(noex)> {
+class function_ref<R(ArgTypes...) cv noexcept(noex)>
+{
 public:
-  template<class F> function_ref(F*) noexcept;
-  template<class F> function_ref(F&&) noexcept;
-  template<auto f> function_ref(nontype_t<f>) noexcept;
-  template<auto f, class U> function_ref(nontype_t<f>, U&&) noexcept;
-  template<auto f, class T> function_ref(nontype_t<f>, cv T*) noexcept;

-  function_ref(const function_ref&) noexcept = default;
-  function_ref& operator=(const function_ref&) noexcept = default;
-  template<class T> function_ref& operator=(T) = delete;
+    template<class F> function_ref(F*) noexcept;
+    template<class F> function_ref(F&&) noexcept;

-  R operator()(ArgTypes...) const noexcept(noex);
+    template<auto f> function_ref(nontype_t<f>) noexcept;
+    template<auto f, class U> function_ref(nontype_t<f>, U&&) noexcept;
+    template<auto f, class T> function_ref(nontype_t<f>, cv T*) noexcept;
+
+    function_ref(const function_ref&) noexcept = default;
+    function_ref& operator=(const function_ref&) noexcept = default;
+    template<class T> function_ref& operator=(T) = delete;
+
+    R operator()(ArgTypes...) const noexcept(noex);
 };

 } // namespace compat
@@ -93,7 +98,7 @@ template<class F> function_ref(F&& fn) noexcept;
 Effects:;; Constructs a `function_ref` that stores the address of the supplied Callable object `fn`. This overload only
 participates in resolution when `fn` is not a pointer-to-member or pointer-to-member-function. +
 +
-Calling the `function_ref` is expression-equivalent to: + `invoke_r<R>(static_cast<cv T&>(f), call-args...)`.
+Calling the `function_ref` is expression-equivalent to `invoke_r<R>(static_cast<cv T&>(f), call-args...)`.

 ### Pointer to Member Function Constructor

@@ -105,7 +110,7 @@ template<auto f> function_ref(nontype_t<f>) noexcept;
 Effects:;; Constructs a `function_ref` using the supplied pointer to member function. This overload only participates
 in resolution when `f` is a pointer to member or pointer to member function. +
 +
-Calling the `function_ref` is express-equivalent to: `invoke_r<R>(f, class-args)`.
+Calling the `function_ref` is expression-equivalent to `invoke_r<R>(f, call-args)`.
 Example:;;
 +
 --
@@ -113,7 +118,7 @@ Example:;;
 struct point { int x = 1, y = 2; };

 point p;
-compat::function_ref<int(point const&)> f(compat::nontype_t<&point::x>{});
+compat::function_ref<int(point const&)> f(compat::nontype<&point::x>);

 BOOST_TEST_EQ(f(p), 1);
 ```
@@ -137,7 +142,7 @@ Example:;;
 struct point { int x = 1, y = 2; };

 point p;
-compat::function_ref<int()> f(compat::nontype_t<&point::x>{}, p);
+compat::function_ref<int()> f(compat::nontype<&point::x>, p);

 BOOST_TEST_EQ(f(), 1);
 ```
@@ -159,7 +164,7 @@ Example:;;
 struct point { int x = 1, y = 2; };

 point p;
-compat::function_ref<int()> f(compat::nontype_t<&point::x>{}, &p);
+compat::function_ref<int()> f(compat::nontype<&point::x>, &p);

 BOOST_TEST_EQ(f(), 1);
 ```
--- a/doc/compat/move_only_function.adoc
+++ b/doc/compat/move_only_function.adoc
@@ -0,0 +1,252 @@
+////
+Copyright 2025 Christian Mazakas
+Distributed under the Boost Software License, Version 1.0.
+https://www.boost.org/LICENSE_1_0.txt
+////
+
+[#move_only_function]
+# <boost/compat/move_only_function.hpp>
+:idprefix: ref_move_only_function_
+
+## Description
+
+The header `<boost/compat/move_only_function.hpp>` implements the {cpp}23 class https://en.cppreference.com/w/cpp/utility/functional/move_only_function.html[std::move_only_function].
+
+`move_only_function` is a polymorphic wrapper that stores and manages a https://en.cppreference.com/w/cpp/named_req/Callable[Callable], only requiring that the type supports move construction and move assignment.
+This is in contrast to the commonly used `std::function` which requires copyability of the underlying managed object.
+
+`move_only_function` supports every combination of `const`, `noexcept` and reference qualification (none, `&`, `&&`).
+
+## Example
+
+```cpp
+struct moveonly
+{
+    std::unique_ptr<int> p_ = std::make_unique<int>( 1234 );
+    auto operator()( int x ) noexcept { return *p_ + x; }
+};
+
+boost::compat::move_only_function<int( int ) noexcept> f( moveonly{} );
+std::cout << f( 4321 ) << std::endl;
+```
+
+## Synopsis
+
+```cpp
+namespace boost {
+namespace compat {
+
+template<class... S>
+class move_only_function;
+
+template< class T >
+struct in_place_type_t { explicit in_place_type_t() = default; };
+
+template<class R, class ...Args>
+class move_only_function<R( Args... ) /* cv */ /* ref */ noexcept( /* noex */)>
+{
+    move_only_function() noexcept;
+    move_only_function( std::nullptr_t ) noexcept;
+
+    template<class F>
+    move_only_function( F&& f );
+
+    template<class T, class ...CArgs>
+    explicit move_only_function( in_place_type_t<T>, CArgs&& ... args );
+
+    template<class T, class U, class ...CArgs>
+    explicit move_only_function( in_place_type_t<T>,
+                                 std::initializer_list<U> il, CArgs&& ... args );
+
+    move_only_function( move_only_function const& ) = delete;
+    move_only_function( move_only_function&& ) = default;
+
+    ~move_only_function() = default;
+
+    move_only_function& operator=( move_only_function&& rhs );
+    move_only_function& operator=( std::nullptr_t ) noexcept;
+    template<class F> move_only_function& operator=( F&& f );
+
+    friend bool operator==( move_only_function const& fn, std::nullptr_t ) noexcept;
+    friend bool operator!=( move_only_function const& fn, std::nullptr_t ) noexcept;
+
+    void swap( move_only_function& rhs ) noexcept;
+    friend void swap( move_only_function& lhs, move_only_function& rhs ) noexcept;
+
+    explicit operator bool() const noexcept;
+
+    R operator()( Args... args ) /* cv */ /* ref */ noexcept( /* noex */ );
+};
+
+} // namespace compat
+} // namespace boost
+
+```
+
+## Constructors
+
+### Default Constructor
+
+```cpp
+move_only_function() noexcept;
+```
+
+[horizontal]
+Effects::
+Constructs an empty `move_only_function` which manages no object.
+
+### Null Constructor
+
+```cpp
+move_only_function( std::nullptr_t ) noexcept;
+```
+
+[horizontal]
+Effects::
+Explicitly constructs an empty `move_only_function` using a nullptr value. Equivalent to default construction.
+
+### Object Constructor
+
+```cpp
+template<class F>
+move_only_function( F&& f );
+```
+
+[horizontal]
+Effects:;; Given `using VT = decay_t<F>`, directly constructs an instance of `VT` using `forward<F>(f)` and stores it as the target object. +
+
+If `F` is an empty function pointer, pointer-to-member or specialization of `move_only_function` then the constructed `move_only_function` is empty.
+Constraints:;;
+
+--
+* `remove_cv_ref<F>` is not the same type as `move_only_function`
+* `remove_cv_ref<F>` is not a specialization of `in_place_type_t`
+* `VT` must be callable with the provided cvref qualifiers and the provided argument types
+--
+
+### In-Place Constructor
+
+```cpp
+template<class T, class ...CArgs>
+explicit move_only_function( in_place_type_t<T>, CArgs&& ... args );
+```
+
+[horizontal]
+Effects:;; Constructs an object of type `T` using the provided args directly, storing it as the target object.
+Constraints:;;
+
+--
+* `is_constructible_v<T, CArgs...>` must be true
+* `T` must be callable with the provided cvref qualifiers and the provided argument types
+--
+
+### List In-Place Constructor
+
+```cpp
+template<class T, class U, class ...CArgs>
+explicit move_only_function( in_place_type_t<T>,
+                             std::initializer_list<U> il, CArgs&& ... args );
+```
+
+[horizontal]
+Effects:;; Constructs an object of type `T` using the provided initializer_list and args directly, storing it as the target Callable.
+Constraints:;;
+
+--
+* `is_constructible_v<T, std::initializer_list<U>&, CArgs...>` must be true
+* `T` must be callable with the provided cvref qualifiers and the provided argument types
+--
+
+### Move Constructor
+
+```cpp
+move_only_function( move_only_function&& f ) = default;
+```
+
+[horizontal]
+Effects::
+Tranfers ownership of the object managed by `f` to `*this`. After this operation completes, `f` is empty and manages no object.
+
+## Assignment
+
+### Move Assignment
+
+```cpp
+move_only_function& operator=( move_only_function&& rhs );
+```
+
+[horizontal]
+Effects:;; Releases the currently managed object and takes ownership of the object managed by `rhs`, if applicable.
+`rhs` is empty after move.
+
+### Null Assigment
+
+```cpp
+move_only_function& operator=( std::nullptr_t ) noexcept;
+```
+
+[horizontal]
+Effects:;; Releases the currently managed object, if applicable.
+
+### Callable Assignment
+
+```cpp
+template<class F> move_only_function& operator=( F&& f );
+```
+
+[horizontal]
+Effects:;; Releases the currently managed object and then does the equivalent of: `move_only_function(std::forward<F>(f)).swap(*this)`.
+
+## Utility
+
+### Null Equality
+
+```cpp
+friend bool operator==( move_only_function const& fn, std::nullptr_t ) noexcept;
+friend bool operator!=( move_only_function const& fn, std::nullptr_t ) noexcept;
+```
+
+[horizontal]
+Effects:;; Returns whether or not `fn` contains a target object.
+
+### Swap
+
+```cpp
+void swap( move_only_function& rhs ) noexcept;
+friend void swap( move_only_function& lhs, move_only_function& rhs ) noexcept;
+```
+
+[horizontal]
+Effects:;; Exchanges the managed objects.
+
+## Invocation
+
+### Boolean Conversion
+
+```cpp
+explicit operator bool() const noexcept;
+```
+
+[horizontal]
+Effects:;; Returns `true` if `*this` is managing an object, or `false` if `*this` is empty.
+
+### Call Operator
+
+```cpp
+R operator()( Args... args ) /* cv */ /* ref */ noexcept( /* noex */ );
+```
+
+[horizontal]
+Preconditions:;; `*this` currently manages an object.
+Effects:;; Invokes the underlying target object. Equivalent to:
+
+--
+```cpp
+return INVOKE<R>(static_cast<F inv-quals>(f), std::forward<Args>(args)...);
+```
+
+where `f` is the target object, and _inv-quals_ is defined by the standard:
+
+* If _ref_ is empty, let _inv-quals_ be _cv&_,
+* otherwise, let _inv-quals_ be _cv ref_.
+--
--- a/doc/compat/nontype.adoc
+++ b/doc/compat/nontype.adoc
@@ -0,0 +1,58 @@
+////
+Copyright 2025 Peter Dimov
+Distributed under the Boost Software License, Version 1.0.
+https://www.boost.org/LICENSE_1_0.txt
+////
+
+[#nontype]
+# <boost/compat/nontype.hpp>
+:idprefix: ref_nontype_
+
+## Description
+
+The header `<boost/compat/nontype.hpp>` provides the {cpp}26 variable
+template `std::nontype`.
+
+`nontype` is used for passing function pointers or member function
+pointers to `function_ref`.
+
+Since `nontype_t` and `nontype` have a template parameter of type
+`auto`, they require {cpp}17. When {cpp}17 isn't available, this
+header can still be included, but doesn't define them. (It would
+have caused an error if it did.)
+
+## Example
+
+```
+struct X
+{
+    void f(int a, int b) const noexcept;
+};
+
+int main()
+{
+    X x;
+    auto fnref = function_ref<void(int, int)>(nontype<&X::f>, &x);
+
+    fnref(1, 2); // calls x.f(1, 2)
+}
+```
+
+## Synopsis
+
+```
+namespace boost
+{
+namespace compat
+{
+
+template<auto V> struct nontype_t
+{
+    explicit nontype_t() = default;
+};
+
+template<auto V> inline constexpr nontype_t<V> nontype {};
+
+} // namespace compat
+} // namespace boost
+```
--- a/doc/compat/reference.adoc
+++ b/doc/compat/reference.adoc
@@ -11,6 +11,8 @@ include::integer_sequence.adoc[]
 include::invoke.adoc[]
 include::latch.adoc[]
 include::mem_fn.adoc[]
+include::move_only_function.adoc[]
 include::shared_lock.adoc[]
 include::to_array.adoc[]
+include::to_underlying.adoc[]
 include::type_traits.adoc[]
--- a/doc/compat/to_array.adoc
+++ b/doc/compat/to_array.adoc
@@ -61,7 +61,7 @@ Type requirements:;; `std::is_constructible_v<remove_cv_t<T>, T&> && !std::is_ar

 ```cpp
 template <class T, std::size_t N>
-constexpr std::array<remove_cvref_t<T>, N> to_array(T (&a)[N]);
+constexpr std::array<remove_cv_t<T>, N> to_array(T (&a)[N]);
 ```

 [horizontal]
--- a/doc/compat/to_underlying.adoc
+++ b/doc/compat/to_underlying.adoc
@@ -0,0 +1,57 @@
+////
+Copyright 2025 Braden Ganetsky
+Distributed under the Boost Software License, Version 1.0.
+https://www.boost.org/LICENSE_1_0.txt
+////
+
+[#to_underlying]
+# <boost/compat/to_underlying.hpp>
+:idprefix: ref_to_underlying_
+
+## Description
+
+The header `<boost/compat/to_underlying.hpp>` implements the {cpp}23 function https://en.cppreference.com/w/cpp/utility/to_underlying.html[std::to_underlying].
+
+`to_underlying` is a terse way of converting a value of enumeration type to its underlying type, avoiding accidental narrowing or widening. This function is ill-formed if the given value is not of enumeration type.
+
+## Example
+
+```cpp
+enum e : std::uint16_t
+{
+    e_value = 5
+};
+auto output = boost::compat::to_underlying(e_value);
+static_assert(std::is_same<decltype(output), std::uint16_t>::value);
+assert((
+    output == 5
+));
+```
+
+## Synopsis
+
+```cpp
+namespace boost
+{
+namespace compat
+{
+
+template <class E>
+constexpr typename std::underlying_type<E>::type to_underlying(E e) noexcept;
+
+} // namespace compat
+} // namespace boost
+```
+
+## to_underlying
+
+```cpp
+template <class E>
+constexpr typename std::underlying_type<E>::type to_underlying(E e) noexcept;
+```
+
+[horizontal]
+Effects:;; Casts the value `e` of enumeration type `E` to its underlying type.
+           Equivalent to `static_cast<typename std::underlying_type<E>::type>(e)`.
+Type requirements:;; `std::is_enum<E>::value`.
+                     Otherwise, the function is ill-formed.
--- a/include/boost/compat/detail/nontype.hpp
+++ b/include/boost/compat/detail/nontype.hpp
@@ -0,0 +1,37 @@
+#ifndef BOOST_COMPAT_NONTYPE_HPP_INCLUDED
+#define BOOST_COMPAT_NONTYPE_HPP_INCLUDED
+
+// Copyright 2024 Christian Mazakas
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+
+namespace boost {
+namespace compat {
+
+namespace detail {
+
+template<class V, V v> struct nttp_holder
+{
+};
+
+} // namespace detail
+
+#if defined(__cpp_nontype_template_parameter_auto) && __cpp_nontype_template_parameter_auto >= 201606L
+
+template<auto V> struct nontype_t: public detail::nttp_holder<decltype(V), V>
+{
+    explicit nontype_t() = default;
+};
+
+template<auto V>
+BOOST_INLINE_CONSTEXPR nontype_t<V> nontype {};
+
+#endif
+
+} // namespace compat
+} // namespace boost
+
+#endif // BOOST_COMPAT_NONTYPE_HPP_INCLUDED
--- a/include/boost/compat/function_ref.hpp
+++ b/include/boost/compat/function_ref.hpp
@@ -5,31 +5,19 @@
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt

+#include <boost/compat/detail/nontype.hpp>
 #include <boost/compat/invoke.hpp>
 #include <boost/compat/type_traits.hpp>

 #include <type_traits>
 #include <utility>

-#if defined(__cpp_nontype_template_parameter_auto) && __cpp_nontype_template_parameter_auto >= 201606L
-#define BOOST_COMPAT_HAS_AUTO_NTTP
-#endif
-
 namespace boost {
 namespace compat {

 template <class... S>
 struct function_ref;

-#if defined(BOOST_COMPAT_HAS_AUTO_NTTP)
-
-template <auto V>
-struct nontype_t {
-  explicit nontype_t() = default;
-};
-
-#endif
-
 namespace detail {

 template <bool NoEx>
@@ -55,16 +43,14 @@ struct invoke_object_holder {
  }
 };

-#if defined(BOOST_COMPAT_HAS_AUTO_NTTP)
-
-template <auto f, bool Const, bool NoEx, class R, class... Args>
+template <class F, F f, bool Const, bool NoEx, class R, class... Args>
 struct invoke_mem_fn_holder {
  static R invoke_mem_fn(thunk_storage<NoEx> /* s */, Args&&... args) noexcept(NoEx) {
    return compat::invoke_r<R>(f, std::forward<Args>(args)...);
  }
 };

-template <auto f, class U, bool Const, bool NoEx, class R, class... Args>
+template <class F, F f, class U, bool Const, bool NoEx, class R, class... Args>
 struct invoke_target_mem_fn_holder {
  static R invoke_mem_fn(thunk_storage<NoEx> s, Args&&... args) noexcept(NoEx) {
    using T = remove_reference_t<U>;
@@ -73,7 +59,7 @@ struct invoke_target_mem_fn_holder {
  }
 };

-template <auto f, class T, bool Const, bool NoEx, class R, class... Args>
+template <class F, F f, class T, bool Const, bool NoEx, class R, class... Args>
 struct invoke_ptr_mem_fn_holder {
  static R invoke_mem_fn(thunk_storage<NoEx> s, Args&&... args) noexcept(NoEx) {
    using cv_T = conditional_t<Const, add_const_t<T>, T>;
@@ -81,8 +67,6 @@ struct invoke_ptr_mem_fn_holder {
  }
 };

-#endif
-
 template <bool Const, bool NoEx, class R, class... Args>
 struct function_ref_base {
 private:
@@ -106,32 +90,28 @@ public:
    thunk_.pobj_ = const_cast<void*>(static_cast<void const*>(std::addressof(fn)));
  }

-#if defined(BOOST_COMPAT_HAS_AUTO_NTTP)
-
-  template <auto f, class F = decltype(f)>
-  function_ref_base(mem_fn_tag, nontype_t<f>)
-      : thunk_{}, invoke_(&invoke_mem_fn_holder<F{f}, Const, NoEx, R, Args...>::invoke_mem_fn) {
+  template <class F, F f>
+  function_ref_base(mem_fn_tag, nttp_holder<F, f>)
+      : thunk_{}, invoke_(&invoke_mem_fn_holder<F, f, Const, NoEx, R, Args...>::invoke_mem_fn) {
    thunk_.pobj_ = nullptr;
  }

-  template <auto f, class U, class F = decltype(f)>
-  function_ref_base(mem_fn_tag, nontype_t<f>, U&& obj)
-      : thunk_{}, invoke_(&invoke_target_mem_fn_holder<F{f}, U, Const, NoEx, R, Args...>::invoke_mem_fn) {
+  template <class F, F f, class U>
+  function_ref_base(mem_fn_tag, nttp_holder<F, f>, U&& obj)
+      : thunk_{}, invoke_(&invoke_target_mem_fn_holder<F, f, U, Const, NoEx, R, Args...>::invoke_mem_fn) {
    thunk_.pobj_ = const_cast<void*>(static_cast<void const*>(std::addressof(obj)));
  }

-  template <auto f, class T, class F = decltype(f)>
-  function_ref_base(mem_fn_tag, nontype_t<f>, T* obj)
-      : thunk_{}, invoke_(&invoke_ptr_mem_fn_holder<F{f}, T, Const, NoEx, R, Args...>::invoke_mem_fn) {
+  template <class F, F f, class T>
+  function_ref_base(mem_fn_tag, nttp_holder<F, f>, T* obj)
+      : thunk_{}, invoke_(&invoke_ptr_mem_fn_holder<F, f, T, Const, NoEx, R, Args...>::invoke_mem_fn) {
    thunk_.pobj_ = const_cast<void*>(static_cast<void const*>(obj));
  }

-#endif
-
  function_ref_base(const function_ref_base&) noexcept = default;
  function_ref_base& operator=(const function_ref_base&) noexcept = default;

-  R operator()(Args&&... args) const noexcept(NoEx) { return this->invoke_(thunk_, std::forward<Args>(args)...); }
+  R operator()(Args... args) const noexcept(NoEx) { return this->invoke_(thunk_, std::forward<Args>(args)...); }
 };

 } // namespace detail
@@ -157,19 +137,15 @@ public:
                        int> = 0>
  function_ref(F&& fn) noexcept : base_type(obj_tag{}, fn) {}

-#if defined(BOOST_COMPAT_HAS_AUTO_NTTP)
+  template <class F, F f, enable_if_t<is_invocable_using<F>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x) noexcept : base_type(mem_fn_tag{}, x) {}

-  template <auto f, class F = decltype(f), enable_if_t<is_invocable_using<F>::value, int> = 0>
-  function_ref(nontype_t<f> x) noexcept : base_type(mem_fn_tag{}, x) {}
+  template <class F, F f, class U, class T = remove_reference_t<U>,
+            enable_if_t<!std::is_rvalue_reference<U&&>::value && is_invocable_using<F, T&>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x, U&& obj) noexcept : base_type(mem_fn_tag{}, x, std::forward<U>(obj)) {}

-  template <auto f, class U, class T = remove_reference_t<U>, class F = decltype(f),
-            enable_if_t<!std::is_rvalue_reference_v<U&&> && is_invocable_using<F, T&>::value, int> = 0>
-  function_ref(nontype_t<f> x, U&& obj) noexcept : base_type(mem_fn_tag{}, x, std::forward<U>(obj)) {}
-
-  template <auto f, class T, class F = decltype(f), enable_if_t<is_invocable_using<F, T*>::value, int> = 0>
-  function_ref(nontype_t<f> x, T* obj) noexcept : base_type(mem_fn_tag{}, x, obj) {}
-
-#endif
+  template <class F, F f, class T, enable_if_t<is_invocable_using<F, T*>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x, T* obj) noexcept : base_type(mem_fn_tag{}, x, obj) {}

  function_ref(const function_ref&) noexcept = default;
  function_ref& operator=(const function_ref&) noexcept = default;
@@ -199,19 +175,15 @@ public:
                        int> = 0>
  function_ref(F&& fn) noexcept : base_type(obj_tag{}, fn) {}

-#if defined(BOOST_COMPAT_HAS_AUTO_NTTP)
+  template <class F, F f, enable_if_t<is_invocable_using<F>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x) noexcept : base_type(mem_fn_tag{}, x) {}

-  template <auto f, class F = decltype(f), enable_if_t<is_invocable_using<F>::value, int> = 0>
-  function_ref(nontype_t<f> x) noexcept : base_type(mem_fn_tag{}, x) {}
+  template <class F, F f, class U, class T = remove_reference_t<U>,
+            enable_if_t<!std::is_rvalue_reference<U&&>::value && is_invocable_using<F, T const&>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x, U&& obj) noexcept : base_type(mem_fn_tag{}, x, std::forward<U>(obj)) {}

-  template <auto f, class U, class T = remove_reference_t<U>, class F = decltype(f),
-            enable_if_t<!std::is_rvalue_reference_v<U&&> && is_invocable_using<F, T const&>::value, int> = 0>
-  function_ref(nontype_t<f> x, U&& obj) noexcept : base_type(mem_fn_tag{}, x, std::forward<U>(obj)) {}
-
-  template <auto f, class T, class F = decltype(f), enable_if_t<is_invocable_using<F, T const*>::value, int> = 0>
-  function_ref(nontype_t<f> x, T const* obj) noexcept : base_type(mem_fn_tag{}, x, obj) {}
-
-#endif
+  template <class F, F f, class T, enable_if_t<is_invocable_using<F, T const*>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x, T const* obj) noexcept : base_type(mem_fn_tag{}, x, obj) {}

  function_ref(const function_ref&) noexcept = default;
  function_ref& operator=(const function_ref&) noexcept = default;
@@ -243,19 +215,15 @@ public:
                        int> = 0>
  function_ref(F&& fn) noexcept : base_type(obj_tag{}, fn) {}

-#if defined(BOOST_COMPAT_HAS_AUTO_NTTP)
+  template <class F, F f, enable_if_t<is_invocable_using<F>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x) noexcept : base_type(mem_fn_tag{}, x) {}

-  template <auto f, class F = decltype(f), enable_if_t<is_invocable_using<F>::value, int> = 0>
-  function_ref(nontype_t<f> x) noexcept : base_type(mem_fn_tag{}, x) {}
+  template <class F, F f, class U, class T = remove_reference_t<U>,
+            enable_if_t<!std::is_rvalue_reference<U&&>::value && is_invocable_using<F, T&>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x, U&& obj) noexcept : base_type(mem_fn_tag{}, x, std::forward<U>(obj)) {}

-  template <auto f, class U, class T = remove_reference_t<U>, class F = decltype(f),
-            enable_if_t<!std::is_rvalue_reference_v<U&&> && is_invocable_using<F, T&>::value, int> = 0>
-  function_ref(nontype_t<f> x, U&& obj) noexcept : base_type(mem_fn_tag{}, x, std::forward<U>(obj)) {}
-
-  template <auto f, class T, class F = decltype(f), enable_if_t<is_invocable_using<F, T*>::value, int> = 0>
-  function_ref(nontype_t<f> x, T* obj) noexcept : base_type(mem_fn_tag{}, x, obj) {}
-
-#endif
+  template <class F, F f, class T, enable_if_t<is_invocable_using<F, T*>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x, T* obj) noexcept : base_type(mem_fn_tag{}, x, obj) {}

  function_ref(const function_ref&) noexcept = default;
  function_ref& operator=(const function_ref&) noexcept = default;
@@ -285,19 +253,15 @@ public:
                        int> = 0>
  function_ref(F&& fn) noexcept : base_type(obj_tag{}, fn) {}

-#if defined(BOOST_COMPAT_HAS_AUTO_NTTP)
+  template <class F, F f, enable_if_t<is_invocable_using<F>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x) noexcept : base_type(mem_fn_tag{}, x) {}

-  template <auto f, class F = decltype(f), enable_if_t<is_invocable_using<F>::value, int> = 0>
-  function_ref(nontype_t<f> x) noexcept : base_type(mem_fn_tag{}, x) {}
+  template <class F, F f, class U, class T = remove_reference_t<U>,
+            enable_if_t<!std::is_rvalue_reference<U&&>::value && is_invocable_using<F, T const&>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x, U&& obj) noexcept : base_type(mem_fn_tag{}, x, std::forward<U>(obj)) {}

-  template <auto f, class U, class T = remove_reference_t<U>, class F = decltype(f),
-            enable_if_t<!std::is_rvalue_reference_v<U&&> && is_invocable_using<F, T const&>::value, int> = 0>
-  function_ref(nontype_t<f> x, U&& obj) noexcept : base_type(mem_fn_tag{}, x, std::forward<U>(obj)) {}
-
-  template <auto f, class T, class F = decltype(f), enable_if_t<is_invocable_using<F, T const*>::value, int> = 0>
-  function_ref(nontype_t<f> x, T const* obj) noexcept : base_type(mem_fn_tag{}, x, obj) {}
-
-#endif
+  template <class F, F f, class T, enable_if_t<is_invocable_using<F, T const*>::value, int> = 0>
+  function_ref(detail::nttp_holder<F, f> x, T const* obj) noexcept : base_type(mem_fn_tag{}, x, obj) {}

  function_ref(const function_ref&) noexcept = default;
  function_ref& operator=(const function_ref&) noexcept = default;
--- a/include/boost/compat/move_only_function.hpp
+++ b/include/boost/compat/move_only_function.hpp
--- a/include/boost/compat/to_underlying.hpp
+++ b/include/boost/compat/to_underlying.hpp
@@ -0,0 +1,22 @@
+#ifndef BOOST_COMPAT_TO_UNDERLYING_HPP_INCLUDED
+#define BOOST_COMPAT_TO_UNDERLYING_HPP_INCLUDED
+
+// Copyright 2025 Braden Ganetsky
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <type_traits>
+
+namespace boost {
+namespace compat {
+
+template <class E>
+constexpr typename std::underlying_type<E>::type to_underlying(E e) noexcept
+{
+    return static_cast<typename std::underlying_type<E>::type>(e);
+}
+
+}  // namespace compat
+}  // namespace boost
+
+#endif  // BOOST_COMPAT_TO_UNDERLYING_HPP_INCLUDED
--- a/include/boost/compat/type_traits.hpp
+++ b/include/boost/compat/type_traits.hpp
@@ -2,7 +2,7 @@
 #define BOOST_COMPAT_TYPE_TRAITS_HPP_INCLUDED

 // Copyright 2024 Peter Dimov
-// Copyright 2024 Christian Mazakas
+// Copyright 2024-2025 Christian Mazakas
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt

@@ -11,10 +11,14 @@
 namespace boost {
 namespace compat {

+template<class T> using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type;
+template<class T> using add_rvalue_reference_t = typename std::add_rvalue_reference<T>::type;
+
 template<class T> using remove_const_t = typename std::remove_const<T>::type;
 template<class T> using remove_cv_t = typename std::remove_cv<T>::type;
 template<class T> using remove_reference_t = typename std::remove_reference<T>::type;
 template<class T> using remove_cvref_t = remove_cv_t< remove_reference_t<T> >;
+template<class T> using remove_pointer_t = typename std::remove_pointer<T>::type;

 template<class T> using decay_t = typename std::decay<T>::type;

@@ -35,6 +39,11 @@ template<class... T> using void_t = typename detail::make_void<T...>::type;

 template<class T> using add_const_t = typename std::add_const<T>::type;

+template<class T> struct type_identity
+{
+    using type = T;
+};
+
 } // namespace compat
 } // namespace boost

--- a/test/Jamfile
+++ b/test/Jamfile
@@ -113,5 +113,11 @@ run function_ref_fn_noexcept_test.cpp ;
 run function_ref_mfn_noexcept_test.cpp ;
 run function_ref_obj_noexcept_test.cpp ;

+run move_only_function_test.cpp ;
+
 run to_array_lvalue_test.cpp ;
 run to_array_rvalue_test.cpp ;
+
+run to_underlying_test.cpp ;
+
+run nontype_test.cpp ;
--- a/test/function_ref_fn_test.cpp
+++ b/test/function_ref_fn_test.cpp
@@ -98,8 +98,9 @@ int main() {

  // f1
  {
+    int x = 1;
    compat::function_ref<int(int)> fv1(f1);
-    BOOST_TEST_EQ(fv1(1), 1);
+    BOOST_TEST_EQ(fv1(x), 1);

    compat::function_ref<int(int) const> fv2(f1);
    BOOST_TEST_EQ(fv2(1), 1);
--- a/test/function_ref_mfn_noexcept_test.cpp
+++ b/test/function_ref_mfn_noexcept_test.cpp
@@ -7,19 +7,23 @@
 #endif

 #include <boost/compat/function_ref.hpp>
-
-#if !defined(BOOST_COMPAT_HAS_AUTO_NTTP)
-#include <boost/config/pragma_message.hpp>
-BOOST_PRAGMA_MESSAGE("no support for placeholder NTTPs detected, skipping this test")
-int main() {}
-#else
-
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/lightweight_test_trait.hpp>
-
 #include <memory>
 #include <type_traits>

+#if defined(__cpp_nontype_template_parameter_auto) && __cpp_nontype_template_parameter_auto >= 201606L
+
+#define NONTYPE(fn) compat::nontype<fn>
+#define NONTYPE_T(fn) compat::nontype_t<fn>
+
+#else
+
+#define NONTYPE(fn) compat::detail::nttp_holder<decltype(fn), fn>{}
+#define NONTYPE_T(fn) compat::detail::nttp_holder<decltype(fn), fn>
+
+#endif
+
 struct F1 {
  std::unique_ptr<int> p_;

@@ -35,130 +39,148 @@ namespace compat = boost::compat;

 int main() {
  {
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(F1&) noexcept>, compat::nontype_t<&F1::m1>>));
+        (std::is_constructible<compat::function_ref<int(F1&) noexcept>, NONTYPE_T(&F1::m1)>));
+#endif
    BOOST_TEST_TRAIT_TRUE(
-        (std::is_constructible<compat::function_ref<int(F1&, int) noexcept>, compat::nontype_t<&F1::m2>>));
+        (std::is_constructible<compat::function_ref<int(F1&, int) noexcept>, NONTYPE_T(&F1::m2)>));
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(F1&, int, int) noexcept>, compat::nontype_t<&F1::m3>>));
+        (std::is_constructible<compat::function_ref<int(F1&, int, int) noexcept>, NONTYPE_T(&F1::m3)>));
+#endif
    BOOST_TEST_TRAIT_TRUE(
-        (std::is_constructible<compat::function_ref<int(F1&, int, int, int) noexcept>, compat::nontype_t<&F1::m4>>));
+        (std::is_constructible<compat::function_ref<int(F1&, int, int, int) noexcept>, NONTYPE_T(&F1::m4)>));
  }

  {
    F1 f1;

-    compat::function_ref<int(F1&, int) noexcept> fn2(compat::nontype_t<&F1::m2>{});
+    compat::function_ref<int(F1&, int) noexcept> fn2(NONTYPE(&F1::m2));
    BOOST_TEST_EQ(fn2(f1, 2), 12);

-    compat::function_ref<int(F1&, int, int, int) noexcept> fn4(compat::nontype_t<&F1::m4>{});
+    compat::function_ref<int(F1&, int, int, int) noexcept> fn4(NONTYPE(&F1::m4));
    BOOST_TEST_EQ(fn4(f1, 2, 3, 4), 1234);
  }

  {
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(F1&) const noexcept>, compat::nontype_t<&F1::m1>>));
+        (std::is_constructible<compat::function_ref<int(F1&) const noexcept>, NONTYPE_T(&F1::m1)>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(F1&, int, int) const noexcept>, compat::nontype_t<&F1::m3>>));
+        (std::is_constructible<compat::function_ref<int(F1&, int, int) const noexcept>, NONTYPE_T(&F1::m3)>));
+#endif

    F1 f1;

-    compat::function_ref<int(F1&, int) const noexcept> fn2(compat::nontype_t<&F1::m2>{});
+    compat::function_ref<int(F1&, int) const noexcept> fn2(NONTYPE(&F1::m2));
    BOOST_TEST_EQ(fn2(f1, 2), 12);

-    compat::function_ref<int(F1&, int, int, int) const noexcept> fn4(compat::nontype_t<&F1::m4>{});
+    compat::function_ref<int(F1&, int, int, int) const noexcept> fn4(NONTYPE(&F1::m4));
    BOOST_TEST_EQ(fn4(f1, 2, 3, 4), 1234);
  }

  {
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(F1 const&) noexcept>, compat::nontype_t<&F1::m1>>));
+        (std::is_constructible<compat::function_ref<int(F1 const&) noexcept>, NONTYPE_T(&F1::m1)>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(F1 const&, int) noexcept>, compat::nontype_t<&F1::m2>>));
+        (std::is_constructible<compat::function_ref<int(F1 const&, int) noexcept>, NONTYPE_T(&F1::m2)>));
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(F1 const&, int, int) noexcept>, compat::nontype_t<&F1::m3>>));
+        (std::is_constructible<compat::function_ref<int(F1 const&, int, int) noexcept>, NONTYPE_T(&F1::m3)>));
+#endif

    F1 f1;

-    compat::function_ref<int(F1 const&, int, int, int) noexcept> fn4(compat::nontype_t<&F1::m4>{});
+    compat::function_ref<int(F1 const&, int, int, int) noexcept> fn4(NONTYPE(&F1::m4));
    BOOST_TEST_EQ(fn4(f1, 2, 3, 4), 1234);
  }

  {
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int() noexcept>, compat::nontype_t<&F1::m1>, F1&>));
+        (std::is_constructible<compat::function_ref<int() noexcept>, NONTYPE_T(&F1::m1), F1&>));
+#endif
    BOOST_TEST_TRAIT_TRUE(
-        (std::is_constructible<compat::function_ref<int(int) noexcept>, compat::nontype_t<&F1::m2>, F1&>));
+        (std::is_constructible<compat::function_ref<int(int) noexcept>, NONTYPE_T(&F1::m2), F1&>));
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int, int) noexcept>, compat::nontype_t<&F1::m3>, F1&>));
+        (std::is_constructible<compat::function_ref<int(int, int) noexcept>, NONTYPE_T(&F1::m3), F1&>));
+#endif
    BOOST_TEST_TRAIT_TRUE(
-        (std::is_constructible<compat::function_ref<int(int, int, int) noexcept>, compat::nontype_t<&F1::m4>, F1&>));
+        (std::is_constructible<compat::function_ref<int(int, int, int) noexcept>, NONTYPE_T(&F1::m4), F1&>));

    F1 f1;

-    compat::function_ref<int(int) noexcept> fn2(compat::nontype_t<&F1::m2>{}, f1);
+    compat::function_ref<int(int) noexcept> fn2(NONTYPE(&F1::m2), f1);
    BOOST_TEST_EQ(fn2(2), 12);

-    compat::function_ref<int(int, int, int) noexcept> fn4(compat::nontype_t<&F1::m4>{}, f1);
+    compat::function_ref<int(int, int, int) noexcept> fn4(NONTYPE(&F1::m4), f1);
    BOOST_TEST_EQ(fn4(2, 3, 4), 1234);
  }

  {
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int() const noexcept>, compat::nontype_t<&F1::m1>, F1 const&>));
+        (std::is_constructible<compat::function_ref<int() const noexcept>, NONTYPE_T(&F1::m1), F1 const&>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int) const noexcept>, compat::nontype_t<&F1::m2>, F1 const&>));
+        (std::is_constructible<compat::function_ref<int(int) const noexcept>, NONTYPE_T(&F1::m2), F1 const&>));
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int(int, int) const noexcept>,
-                                                  compat::nontype_t<&F1::m3>, F1 const&>));
+                                                  NONTYPE_T(&F1::m3), F1 const&>));
+#endif

    F1 f1;

-    compat::function_ref<int(int, int, int) const noexcept> fn4(compat::nontype_t<&F1::m4>{}, f1);
+    compat::function_ref<int(int, int, int) const noexcept> fn4(NONTYPE(&F1::m4), f1);
    BOOST_TEST_EQ(fn4(2, 3, 4), 1234);

    auto const& f1_2 = f1;
-    compat::function_ref<int(int, int, int) const noexcept> fn4_2(compat::nontype_t<&F1::m4>{}, f1_2);
+    compat::function_ref<int(int, int, int) const noexcept> fn4_2(NONTYPE(&F1::m4), f1_2);
    BOOST_TEST_EQ(fn4_2(2, 3, 4), 1234);
  }

  {
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int() noexcept>, compat::nontype_t<&F1::m1>, F1*>));
+        (std::is_constructible<compat::function_ref<int() noexcept>, NONTYPE_T(&F1::m1), F1*>));
+#endif
    BOOST_TEST_TRAIT_TRUE(
-        (std::is_constructible<compat::function_ref<int(int) noexcept>, compat::nontype_t<&F1::m2>, F1*>));
+        (std::is_constructible<compat::function_ref<int(int) noexcept>, NONTYPE_T(&F1::m2), F1*>));
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int, int) noexcept>, compat::nontype_t<&F1::m3>, F1*>));
+        (std::is_constructible<compat::function_ref<int(int, int) noexcept>, NONTYPE_T(&F1::m3), F1*>));
+#endif
    BOOST_TEST_TRAIT_TRUE(
-        (std::is_constructible<compat::function_ref<int(int, int, int) noexcept>, compat::nontype_t<&F1::m4>, F1*>));
+        (std::is_constructible<compat::function_ref<int(int, int, int) noexcept>, NONTYPE_T(&F1::m4), F1*>));

    F1 f1;

-    compat::function_ref<int(int) noexcept> fn2(compat::nontype_t<&F1::m2>{}, &f1);
+    compat::function_ref<int(int) noexcept> fn2(NONTYPE(&F1::m2), &f1);
    BOOST_TEST_EQ(fn2(2), 12);

-    compat::function_ref<int(int, int, int) noexcept> fn4(compat::nontype_t<&F1::m4>{}, &f1);
+    compat::function_ref<int(int, int, int) noexcept> fn4(NONTYPE(&F1::m4), &f1);
    BOOST_TEST_EQ(fn4(2, 3, 4), 1234);
  }

  {
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int() const noexcept>, compat::nontype_t<&F1::m1>, F1 const*>));
+        (std::is_constructible<compat::function_ref<int() const noexcept>, NONTYPE_T(&F1::m1), F1 const*>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int) const noexcept>, compat::nontype_t<&F1::m2>, F1 const*>));
+        (std::is_constructible<compat::function_ref<int(int) const noexcept>, NONTYPE_T(&F1::m2), F1 const*>));
+#if defined(__cpp_noexcept_function_types)
    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int(int, int) const noexcept>,
-                                                  compat::nontype_t<&F1::m3>, F1 const*>));
+                                                  NONTYPE_T(&F1::m3), F1 const*>));
+#endif

    F1 const f1;

-    compat::function_ref<int(int, int, int) const noexcept> fn4(compat::nontype_t<&F1::m4>{}, &f1);
+    compat::function_ref<int(int, int, int) const noexcept> fn4(NONTYPE(&F1::m4), &f1);
    BOOST_TEST_EQ(fn4(2, 3, 4), 1234);

    auto const& f1_2 = f1;
-    compat::function_ref<int(int, int, int) const noexcept> fn4_2(compat::nontype_t<&F1::m4>{}, &f1_2);
+    compat::function_ref<int(int, int, int) const noexcept> fn4_2(NONTYPE(&F1::m4), &f1_2);
    BOOST_TEST_EQ(fn4_2(2, 3, 4), 1234);
  }

  return boost::report_errors();
 }
-
-#endif
--- a/test/function_ref_mfn_test.cpp
+++ b/test/function_ref_mfn_test.cpp
@@ -7,19 +7,23 @@
 #endif

 #include <boost/compat/function_ref.hpp>
-
-#if !defined(BOOST_COMPAT_HAS_AUTO_NTTP)
-#include <boost/config/pragma_message.hpp>
-BOOST_PRAGMA_MESSAGE("no support for placeholder NTTPs detected, skipping this test")
-int main() {}
-#else
-
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/lightweight_test_trait.hpp>
-
 #include <memory>
 #include <type_traits>

+#if defined(__cpp_nontype_template_parameter_auto) && __cpp_nontype_template_parameter_auto >= 201606L
+
+#define NONTYPE(fn) compat::nontype<fn>
+#define NONTYPE_T(fn) compat::nontype_t<fn>
+
+#else
+
+#define NONTYPE(fn) compat::detail::nttp_holder<decltype(fn), fn>{}
+#define NONTYPE_T(fn) compat::detail::nttp_holder<decltype(fn), fn>
+
+#endif
+
 struct F1 {
  std::unique_ptr<int> p_;
  int q_ = 1337;
@@ -38,120 +42,121 @@ int main() {
  {
    F1 f1;

-    compat::function_ref<int(F1&)> fn1(compat::nontype_t<&F1::m1>{});
+    compat::function_ref<int(F1&)> fn1(NONTYPE(&F1::m1));
    BOOST_TEST_EQ(fn1(f1), 0);

-    compat::function_ref<int(F1&, int)> fn2(compat::nontype_t<&F1::m2>{});
-    BOOST_TEST_EQ(fn2(f1, 2), 12);
+    int x = 2;
+    compat::function_ref<int(F1&, int)> fn2(NONTYPE(&F1::m2));
+    BOOST_TEST_EQ(fn2(f1, x), 12);

-    compat::function_ref<int(F1&, int, int)> fn3(compat::nontype_t<&F1::m3>{});
+    compat::function_ref<int(F1&, int, int)> fn3(NONTYPE(&F1::m3));
    BOOST_TEST_EQ(fn3(f1, 2, 3), 123);

-    compat::function_ref<int(F1&, int, int, int)> fn4(compat::nontype_t<&F1::m4>{});
+    compat::function_ref<int(F1&, int, int, int)> fn4(NONTYPE(&F1::m4));
    BOOST_TEST_EQ(fn4(f1, 2, 3, 4), 1234);

-    compat::function_ref<int(F1&)> a1(compat::nontype_t<&F1::q_>{});
+    compat::function_ref<int(F1&)> a1(NONTYPE(&F1::q_));
    BOOST_TEST_EQ(a1(f1), 1337);
  }

  {
    F1 f1;

-    compat::function_ref<int(F1&) const> fn1(compat::nontype_t<&F1::m1>{});
+    compat::function_ref<int(F1&) const> fn1(NONTYPE(&F1::m1));
    BOOST_TEST_EQ(fn1(f1), 0);

-    compat::function_ref<int(F1&, int) const> fn2(compat::nontype_t<&F1::m2>{});
+    compat::function_ref<int(F1&, int) const> fn2(NONTYPE(&F1::m2));
    BOOST_TEST_EQ(fn2(f1, 2), 12);

-    compat::function_ref<int(F1&, int, int) const> fn3(compat::nontype_t<&F1::m3>{});
+    compat::function_ref<int(F1&, int, int) const> fn3(NONTYPE(&F1::m3));
    BOOST_TEST_EQ(fn3(f1, 2, 3), 123);

-    compat::function_ref<int(F1&, int, int, int) const> fn4(compat::nontype_t<&F1::m4>{});
+    compat::function_ref<int(F1&, int, int, int) const> fn4(NONTYPE(&F1::m4));
    BOOST_TEST_EQ(fn4(f1, 2, 3, 4), 1234);
  }

  {
-    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int(F1 const&)>, compat::nontype_t<&F1::m1>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int(F1 const&)>, NONTYPE_T(&F1::m1)>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(F1 const&, int)>, compat::nontype_t<&F1::m2>>));
+        (std::is_constructible<compat::function_ref<int(F1 const&, int)>, NONTYPE_T(&F1::m2)>));

    F1 f1;

-    compat::function_ref<int(F1 const&, int, int) const> fn3(compat::nontype_t<&F1::m3>{});
+    compat::function_ref<int(F1 const&, int, int) const> fn3(NONTYPE(&F1::m3));
    BOOST_TEST_EQ(fn3(f1, 2, 3), 123);

-    compat::function_ref<int(F1 const&, int, int, int) const> fn4(compat::nontype_t<&F1::m4>{});
+    compat::function_ref<int(F1 const&, int, int, int) const> fn4(NONTYPE(&F1::m4));
    BOOST_TEST_EQ(fn4(f1, 2, 3, 4), 1234);

    auto const& f2 = f1;

-    compat::function_ref<int(F1 const&, int, int) const> fn23(compat::nontype_t<&F1::m3>{});
+    compat::function_ref<int(F1 const&, int, int) const> fn23(NONTYPE(&F1::m3));
    BOOST_TEST_EQ(fn3(f2, 2, 3), 123);

-    compat::function_ref<int(F1 const&, int, int, int) const> fn24(compat::nontype_t<&F1::m4>{});
+    compat::function_ref<int(F1 const&, int, int, int) const> fn24(NONTYPE(&F1::m4));
    BOOST_TEST_EQ(fn4(f2, 2, 3, 4), 1234);
  }

  {
-    BOOST_TEST_TRAIT_TRUE((std::is_constructible<compat::function_ref<int(int)>, compat::nontype_t<&F1::m2>, F1&>));
+    BOOST_TEST_TRAIT_TRUE((std::is_constructible<compat::function_ref<int(int)>, NONTYPE_T(&F1::m2), F1&>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int)>, compat::nontype_t<&F1::m2>, F1 const&>));
-    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int(int)>, compat::nontype_t<&F1::m2>, F1&&>));
-    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int(int)>, compat::nontype_t<&F1::m2>, F1>));
+        (std::is_constructible<compat::function_ref<int(int)>, NONTYPE_T(&F1::m2), F1 const&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int(int)>, NONTYPE_T(&F1::m2), F1&&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int(int)>, NONTYPE_T(&F1::m2), F1>));

    BOOST_TEST_TRAIT_TRUE(
-        (std::is_constructible<compat::function_ref<int(int, int) const>, compat::nontype_t<&F1::m3>, F1&>));
+        (std::is_constructible<compat::function_ref<int(int, int) const>, NONTYPE_T(&F1::m3), F1&>));
    BOOST_TEST_TRAIT_TRUE(
-        (std::is_constructible<compat::function_ref<int(int, int) const>, compat::nontype_t<&F1::m3>, F1 const&>));
+        (std::is_constructible<compat::function_ref<int(int, int) const>, NONTYPE_T(&F1::m3), F1 const&>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int, int) const>, compat::nontype_t<&F1::m3>, F1&&>));
+        (std::is_constructible<compat::function_ref<int(int, int) const>, NONTYPE_T(&F1::m3), F1&&>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int, int) const>, compat::nontype_t<&F1::m3>, F1>));
+        (std::is_constructible<compat::function_ref<int(int, int) const>, NONTYPE_T(&F1::m3), F1>));
  }

  {
    F1 f1;

-    compat::function_ref<int()> fn1(compat::nontype_t<&F1::m1>{}, f1);
+    compat::function_ref<int()> fn1(NONTYPE(&F1::m1), f1);
    BOOST_TEST_EQ(fn1(), 0);

-    compat::function_ref<int(int)> fn2(compat::nontype_t<&F1::m2>{}, f1);
+    compat::function_ref<int(int)> fn2(NONTYPE(&F1::m2), f1);
    BOOST_TEST_EQ(fn2(2), 12);

-    compat::function_ref<int(int, int)> fn3(compat::nontype_t<&F1::m3>{}, f1);
+    compat::function_ref<int(int, int)> fn3(NONTYPE(&F1::m3), f1);
    BOOST_TEST_EQ(fn3(2, 3), 123);

-    compat::function_ref<int(int, int, int)> fn4(compat::nontype_t<&F1::m4>{}, f1);
+    compat::function_ref<int(int, int, int)> fn4(NONTYPE(&F1::m4), f1);
    BOOST_TEST_EQ(fn4(2, 3, 4), 1234);
  }

  {
    F1 const f1;

-    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int() const>, compat::nontype_t<&F1::m1>, F1&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<int() const>, NONTYPE_T(&F1::m1), F1&>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int) const>, compat::nontype_t<&F1::m2>, F1&>));
+        (std::is_constructible<compat::function_ref<int(int) const>, NONTYPE_T(&F1::m2), F1&>));

-    compat::function_ref<int(int, int) const> fn3(compat::nontype_t<&F1::m3>{}, f1);
+    compat::function_ref<int(int, int) const> fn3(NONTYPE(&F1::m3), f1);
    BOOST_TEST_EQ(fn3(2, 3), 123);

-    compat::function_ref<int(int, int, int) const> fn4(compat::nontype_t<&F1::m4>{}, f1);
+    compat::function_ref<int(int, int, int) const> fn4(NONTYPE(&F1::m4), f1);
    BOOST_TEST_EQ(fn4(2, 3, 4), 1234);
  }

  {
    F1 f1;

-    compat::function_ref<int()> fn1(compat::nontype_t<&F1::m1>{}, &f1);
+    compat::function_ref<int()> fn1(NONTYPE(&F1::m1), &f1);
    BOOST_TEST_EQ(fn1(), 0);

-    compat::function_ref<int(int)> fn2(compat::nontype_t<&F1::m2>{}, &f1);
+    compat::function_ref<int(int)> fn2(NONTYPE(&F1::m2), &f1);
    BOOST_TEST_EQ(fn2(2), 12);

-    compat::function_ref<int(int, int)> fn3(compat::nontype_t<&F1::m3>{}, &f1);
+    compat::function_ref<int(int, int)> fn3(NONTYPE(&F1::m3), &f1);
    BOOST_TEST_EQ(fn3(2, 3), 123);

-    compat::function_ref<int(int, int, int)> fn4(compat::nontype_t<&F1::m4>{}, &f1);
+    compat::function_ref<int(int, int, int)> fn4(NONTYPE(&F1::m4), &f1);
    BOOST_TEST_EQ(fn4(2, 3, 4), 1234);
  }

@@ -159,18 +164,16 @@ int main() {
    F1 const f1;

    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int() const>, compat::nontype_t<&F1::m1>, F1 const*>));
+        (std::is_constructible<compat::function_ref<int() const>, NONTYPE_T(&F1::m1), F1 const*>));
    BOOST_TEST_TRAIT_FALSE(
-        (std::is_constructible<compat::function_ref<int(int) const>, compat::nontype_t<&F1::m2>, F1 const*>));
+        (std::is_constructible<compat::function_ref<int(int) const>, NONTYPE_T(&F1::m2), F1 const*>));

-    compat::function_ref<int(int, int) const> fn3(compat::nontype_t<&F1::m3>{}, &f1);
+    compat::function_ref<int(int, int) const> fn3(NONTYPE(&F1::m3), &f1);
    BOOST_TEST_EQ(fn3(2, 3), 123);

-    compat::function_ref<int(int, int, int) const> fn4(compat::nontype_t<&F1::m4>{}, &f1);
+    compat::function_ref<int(int, int, int) const> fn4(NONTYPE(&F1::m4), &f1);
    BOOST_TEST_EQ(fn4(2, 3, 4), 1234);
  }

  return boost::report_errors();
 }
-
-#endif
--- a/test/function_ref_obj_test.cpp
+++ b/test/function_ref_obj_test.cpp
@@ -65,8 +65,8 @@ int main() {
      BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<S1>, F1 const&&>));

      compat::function_ref<S2> fv2(f);
-
-      BOOST_TEST_EQ(fv2(1), 1);
+      int x = 1;
+      BOOST_TEST_EQ(fv2(x), 1);

      BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<S2>, F1 const>));
      BOOST_TEST_TRAIT_FALSE((std::is_constructible<compat::function_ref<S2>, F1 const&>));
--- a/test/move_only_function_test.cpp
+++ b/test/move_only_function_test.cpp
@@ -0,0 +1,855 @@
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
+
+#if BOOST_WORKAROUND(BOOST_GCC, >= 7 * 10000 && BOOST_GCC < 8 * 10000)
+#   pragma GCC diagnostic push
+#   pragma GCC diagnostic ignored "-Wnoexcept-type"
+#endif
+
+#include <boost/compat/move_only_function.hpp>
+
+#include <boost/compat/invoke.hpp>
+
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+#include <functional>
+#include <memory>
+#include <type_traits>
+
+#if BOOST_WORKAROUND(BOOST_GCC, >= 13 * 10000)
+#   pragma GCC diagnostic push
+#   pragma GCC diagnostic ignored "-Wself-move"
+#elif defined(BOOST_CLANG)
+#   pragma clang diagnostic push
+#   pragma clang diagnostic ignored "-Wself-move"
+#endif
+
+using std::is_same;
+using std::is_constructible;
+using std::is_nothrow_constructible;
+
+using boost::compat::move_only_function;
+using boost::compat::in_place_type_t;
+// using std::move_only_function;
+// using std::in_place_type_t;
+using boost::compat::invoke_result_t;
+using boost::compat::is_invocable;
+using boost::compat::is_nothrow_invocable;
+
+template<class T>
+using add_const_t = typename std::add_const<T>::type;
+
+template<class T>
+constexpr add_const_t<T>& as_const_ref( T& t ) noexcept
+{
+    return t;
+}
+
+void func0() {}
+
+int func1()
+{
+    return 1;
+}
+
+int func2( int x )
+{
+    return x + 1;
+}
+
+int func3( std::unique_ptr<int> x )
+{
+    return *x + 1;
+}
+
+template<class T, class ...Args>
+std::unique_ptr<T> make_unique( Args&&... args )
+{
+    return std::unique_ptr<T>( new T( std::forward<Args>( args )... ) );
+}
+
+struct callable
+{
+    std::unique_ptr<int> p_ = make_unique<int>( 1 );
+
+    callable() = default;
+
+    callable( std::unique_ptr<int> p ): p_( std::move( p ) )
+    {
+    }
+
+    callable( std::initializer_list<int> il, int x, int y, int z )
+    {
+        int sum = 0;
+        for( auto const v : il )
+        {
+            sum += v;
+        }
+        sum += x;
+        sum += y;
+        sum += z;
+        p_ = make_unique<int>( sum );
+    }
+
+    callable( callable&& rhs ) noexcept
+    {
+        p_ = make_unique<int>( *rhs.p_ );
+    }
+
+    int operator()( int x )
+    {
+        return *p_ + x;
+    }
+};
+
+struct noex_callable
+{
+    std::unique_ptr<int> p_ = make_unique<int>( 1 );
+
+    noex_callable() = default;
+    noex_callable( noex_callable&& rhs ) noexcept
+    {
+        p_ = make_unique<int>( *rhs.p_ );
+    }
+
+    noex_callable( noex_callable const& )
+    {
+    }
+
+    int operator()( int x ) noexcept
+    {
+        return *p_ + x;
+    }
+};
+
+struct large_callable
+{
+    unsigned char padding[ 256 ] = {};
+    std::unique_ptr<int> p_ = make_unique<int>( 1 );
+
+    large_callable() = default;
+
+    large_callable( std::unique_ptr<int> p ): p_( std::move( p ) )
+    {
+    }
+
+    large_callable( large_callable&& rhs ) noexcept
+    {
+        p_ = make_unique<int>( *rhs.p_ );
+    }
+
+    int operator()( int x )
+    {
+        return *p_ + x;
+    }
+
+    int operator()( int x, int y )
+    {
+        return x + y;
+    }
+};
+
+struct person
+{
+    std::string name_;
+    int age_ = -1;
+    std::unique_ptr<int> p_ = make_unique<int>( 1 );
+
+    int age()
+    {
+        return age_;
+    }
+};
+
+static void test_call()
+{
+    {
+        move_only_function<int()> f1;
+        BOOST_TEST( !f1 );
+
+        move_only_function<int() const> f2;
+        BOOST_TEST( !f2 );
+    }
+
+    {
+        move_only_function<int()> f1( nullptr );
+        BOOST_TEST( !f1 );
+
+        move_only_function<int() const> f2( nullptr );
+        BOOST_TEST( !f2 );
+    }
+
+    {
+        move_only_function<void()> f1( func0 );
+        f1();
+        BOOST_TEST( f1 );
+
+        move_only_function<void() const> f2( func0 );
+        f2();
+        BOOST_TEST( f2 );
+    }
+
+    {
+        int ( *fp )() = [] { return 0; };
+
+        move_only_function<int()> f1( fp );
+        BOOST_TEST( f1 );
+        BOOST_TEST_EQ( f1(), 0 );
+        BOOST_TEST_EQ( std::move( f1() ), 0 );
+
+        move_only_function<int() const> f2( fp );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2(), 0 );
+        BOOST_TEST_EQ( std::move( f2() ), 0 );
+
+        fp = nullptr;
+        move_only_function<int() const> f3( fp );
+        BOOST_TEST_NOT( f3 );
+    }
+
+    {
+        struct declared;
+        enum class integer : int;
+
+        move_only_function<void(declared)> f1;
+        move_only_function<void(declared&)> f2;
+        move_only_function<void(declared&&)> f3;
+        move_only_function<void(integer)> f4;
+    }
+
+    {
+        move_only_function<int()> f1( func1 );
+        BOOST_TEST( f1 );
+        BOOST_TEST_EQ( f1(), 1 );
+        BOOST_TEST_EQ( std::move( f1() ), 1 );
+
+        move_only_function<int() const> f2( func1 );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2(), 1 );
+        BOOST_TEST_EQ( std::move( f2() ), 1 );
+    }
+
+    {
+        move_only_function<int( std::unique_ptr<int> )> fn( func3 );
+        BOOST_TEST_EQ( fn( make_unique<int>( 1 ) ), 2 );
+        BOOST_TEST_EQ( std::move( fn )( make_unique<int>( 1 ) ), 2 );
+
+        auto x = make_unique<int>( 1 );
+        BOOST_TEST( fn );
+        BOOST_TEST_EQ( fn( std::move( x ) ), 2 );
+    }
+
+    {
+        auto l = []() { return 1; };
+
+        move_only_function<int()> f1( l );
+        BOOST_TEST( f1 );
+        BOOST_TEST_EQ( f1(), 1 );
+        BOOST_TEST_EQ( std::move( f1 )(), 1 );
+
+        move_only_function<int() const> f2( l );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2(), 1 );
+        BOOST_TEST_EQ( as_const_ref( f2 )(), 1 );
+        BOOST_TEST_EQ( std::move( f2 )(), 1 );
+        BOOST_TEST_EQ( std::move( as_const_ref( f2 ) )(), 1 );
+    }
+
+    {
+        move_only_function<int()> f1( []() { return 1; } );
+        BOOST_TEST( f1 );
+        BOOST_TEST_EQ( f1(), 1 );
+        BOOST_TEST_EQ( std::move( f1 )(), 1 );
+
+        move_only_function<int() const> f2( []() { return 1; } );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2(), 1 );
+        BOOST_TEST_EQ( as_const_ref( f2 )(), 1 );
+        BOOST_TEST_EQ( std::move( f2 )(), 1 );
+        BOOST_TEST_EQ( std::move( as_const_ref( f2 ) )(), 1 );
+    }
+
+    {
+        auto l = []( int x ) { return x + 1; };
+
+        move_only_function<int( int )> f1( l );
+        BOOST_TEST( f1 );
+        BOOST_TEST_EQ( f1( 1 ), 2 );
+
+        move_only_function<int( int ) const> f2( l );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2( 1 ), 2 );
+    }
+
+    {
+        auto l = []( std::unique_ptr<int> x ) { return *x + 1; };
+        move_only_function<int( std::unique_ptr<int> )> f( std::move( l ) );
+        BOOST_TEST( f );
+        BOOST_TEST_EQ( f( make_unique<int>( 1 ) ), 2 );
+    }
+
+    {
+        auto p = make_unique<int>( 1 );
+        auto l = []( std::unique_ptr<int>& x ) { return *x + 1; };
+        move_only_function<int( std::unique_ptr<int>& )> f( l );
+        BOOST_TEST( f );
+        BOOST_TEST_EQ( f( p ), 2 );
+    }
+
+    {
+        int x = 1;
+        move_only_function<int( int )> f1( callable{} );
+        BOOST_TEST( f1 );
+        BOOST_TEST_EQ( f1( 1 ), 2);
+        BOOST_TEST_EQ( f1( x ), 2 );
+
+        int y = 2;
+        callable c;
+        move_only_function<int( int )> f2( std::move( c ) );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2( 2 ), 3 );
+        BOOST_TEST_EQ( f2( y ), 3 );
+    }
+
+    {
+        move_only_function<int( int, int )> f1( large_callable{} );
+        BOOST_TEST( f1 );
+        BOOST_TEST_EQ( f1( 1, 2 ), 3);
+
+        large_callable c;
+        move_only_function<int( int, int )> f2( std::move( c ) );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2( 1, 2 ), 3 );
+    }
+
+    {
+        move_only_function<int( int )> f1( in_place_type_t<callable>{}, make_unique<int>( 4321 ) );
+        BOOST_TEST_EQ( f1( 1234 ), 5555 );
+
+        move_only_function<int( int )> f2( in_place_type_t<large_callable>{}, make_unique<int>( 4321 ) );
+        BOOST_TEST_EQ( f2( 1234 ), 5555 );
+
+        move_only_function<int( int )> f3( in_place_type_t<int(*)( int )>{}, func2 );
+        BOOST_TEST_EQ( f3( 1233 ), 1234 );
+
+        move_only_function<int( int )> f4( in_place_type_t<int(*)( int )>{} );
+        BOOST_TEST( f4 != nullptr );
+
+        move_only_function<int( int )> f5( in_place_type_t<callable>{}, std::initializer_list<int>{ 1, 2, 3 }, 4, 5, 6 );
+        BOOST_TEST_EQ( f5( 7 ), 1 + 2 + 3 + 4 + 5 + 6 + 7 );
+    }
+
+    {
+        move_only_function<int()> f1( func1 );
+        move_only_function<int()> f2( std::move( f1 ) );
+
+        BOOST_TEST( !f1 );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2(), 1 );
+    }
+
+    {
+        move_only_function<int( int )> f1( callable{} );
+        move_only_function<int( int )> f2( std::move( f1 ) );
+
+        BOOST_TEST( !f1 );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2( 2 ), 3 );
+    }
+
+    {
+        move_only_function<int( int, int )> f1( large_callable{} );
+        move_only_function<int( int, int )> f2( std::move( f1 ) );
+
+        BOOST_TEST( !f1 );
+        BOOST_TEST( f2 );
+        BOOST_TEST_EQ( f2( 1, 2 ), 3 );
+    }
+
+    {
+        person p;
+        p.age_ = 35;
+
+        move_only_function<int( person& )> f1( &person::age_ );
+        BOOST_TEST_EQ( f1( p ), 35 );
+
+        p.age_ = 53;
+
+        move_only_function<int( person& )> f2( &person::age );
+        BOOST_TEST_EQ( f2( p ), 53 );
+
+        int person::*mp = nullptr;
+        move_only_function<int( person& )> f3( mp );
+        BOOST_TEST_NOT( f3 );
+
+        int (person::*mfp)() = nullptr;
+        move_only_function<int( person& )> f4( mfp );
+        BOOST_TEST_NOT( f4 );
+    }
+
+    {
+        struct tester
+        {
+            int operator()()
+            {
+                return 1;
+            }
+
+            int operator()() const
+            {
+                return 2;
+            }
+        };
+
+        tester t;
+
+        move_only_function<int()> f1( t );
+        move_only_function<int() const> f2( t );
+
+        BOOST_TEST_EQ( f1(), 1 );
+        BOOST_TEST_EQ( std::move( f1 )(), 1 );
+        BOOST_TEST_EQ( f2(), 2 );
+        BOOST_TEST_EQ( as_const_ref( f2 )(), 2 );
+        BOOST_TEST_EQ( std::move( as_const_ref( f2 ) )(), 2 );
+    }
+
+    {
+        struct tester
+        {
+            int operator()() noexcept
+            {
+                return 1;
+            }
+
+            int operator()() const noexcept
+            {
+                return 2;
+            }
+        };
+
+        tester t;
+
+        move_only_function<int() noexcept> f1( t );
+        move_only_function<int() const noexcept> f2( t );
+
+        BOOST_TEST_EQ( f1(), 1 );
+        BOOST_TEST_EQ( std::move( f1 )(), 1 );
+        BOOST_TEST_EQ( f2(), 2 );
+        BOOST_TEST_EQ( as_const_ref( f2 )(), 2 );
+        BOOST_TEST_EQ( std::move( as_const_ref( f2 ) )(), 2 );
+    }
+
+    {
+        struct tester
+        {
+            int operator()() &
+            {
+                return 1;
+            }
+
+            int operator()() &&
+            {
+                return 2;
+            }
+
+            int operator()() const&
+            {
+                return 3;
+            }
+
+            int operator()() const&&
+            {
+                return 4;
+            }
+        };
+
+        tester t;
+
+        move_only_function<int() &> f1( t );
+        move_only_function<int() &&> f2( t );
+        move_only_function<int() const&> f3( t );
+
+        BOOST_TEST_EQ( f1(), 1 );
+        BOOST_TEST_EQ( std::move( f2 )(), 2 );
+        BOOST_TEST_EQ( f3(), 3 );
+        BOOST_TEST_EQ( as_const_ref( f3 )(), 3 );
+
+#if !BOOST_WORKAROUND(BOOST_GCC, < 40900)
+
+        move_only_function<int() const&&> f4( t );
+        BOOST_TEST_EQ( std::move( f4 )(), 4 );
+        BOOST_TEST_EQ( std::move( as_const_ref( f4 ) )(), 4 );
+
+#endif
+    }
+
+    {
+        struct tester
+        {
+            int operator()() & noexcept
+            {
+                return 1;
+            }
+
+            int operator()() && noexcept
+            {
+                return 2;
+            }
+
+            int operator()() const& noexcept
+            {
+                return 3;
+            }
+
+            int operator()() const&& noexcept
+            {
+                return 4;
+            }
+        };
+
+        tester t;
+
+        move_only_function<int() &> f1( t );
+        move_only_function<int() &&> f2( t );
+        move_only_function<int() const&> f3( t );
+
+        BOOST_TEST_EQ( f1(), 1 );
+        BOOST_TEST_EQ( std::move( f2 )(), 2 );
+        BOOST_TEST_EQ( f3(), 3 );
+        BOOST_TEST_EQ( as_const_ref( f3 )(), 3 );
+
+#if !BOOST_WORKAROUND(BOOST_GCC, < 40900)
+
+        move_only_function<int() const&&> f4( t );
+        BOOST_TEST_EQ( std::move( f4 )(), 4 );
+        BOOST_TEST_EQ( std::move( as_const_ref( f4 ) )(), 4 );
+
+#endif
+    }
+
+    {
+        move_only_function<int( int )> f1( callable{} );
+        // f1 = std::move( f1 );
+        // BOOST_TEST_EQ( f1( 1233 ), 1234 );
+
+        move_only_function<int( int )> f2( large_callable{} );
+        f2 = std::move( f1 );
+        BOOST_TEST_EQ( f2( 1233 ), 1234 );
+        BOOST_TEST_NOT( f1 );
+
+        move_only_function<int( int )> f3( callable{} );
+        move_only_function<int( int )> f4( large_callable{} );
+        f3 = std::move( f4 );
+        BOOST_TEST_EQ( f3( 1233 ), 1234 );
+        BOOST_TEST_NOT( f4 );
+
+        move_only_function<int( int )> f5( callable{} );
+        f5 = nullptr;
+        BOOST_TEST_NOT( f5 );
+
+        move_only_function<int( int )> f6( large_callable{} );
+        f6 = nullptr;
+        BOOST_TEST_NOT( f6 );
+
+        move_only_function<int( int )> f7;
+        f7 = nullptr;
+        BOOST_TEST_NOT( f7 );
+
+        move_only_function<int( int )> f8( callable{} );
+        f8 = large_callable{};
+        BOOST_TEST_EQ( f8( 1233 ), 1234 );
+
+        move_only_function<int( int )> f9( large_callable{} );
+        f9 = callable{};
+        BOOST_TEST_EQ( f9( 1233 ), 1234 );
+
+        move_only_function<int( int )> f10;
+        f10 = callable{};
+        BOOST_TEST_EQ( f10( 1233 ), 1234 );
+
+        move_only_function<int( int )> f11;
+        f11 = large_callable{};
+        BOOST_TEST_EQ( f11( 1233 ), 1234 );
+    }
+
+    {
+        callable c1;
+        *c1.p_ = 1234;
+
+        large_callable c2;
+        *c2.p_ = 4321;
+
+        move_only_function<int( int )> f1( std::move( c1 ) );
+        move_only_function<int( int )> f2( std::move( c2 ) );
+
+        int x = 1;
+
+        BOOST_TEST_EQ( f1( x ), 1235 );
+        BOOST_TEST_EQ( f2( x ), 4322 );
+
+        swap( f1, f2 );
+
+        BOOST_TEST_EQ( f1( x ), 4322 );
+        BOOST_TEST_EQ( f2( x ), 1235 );
+
+        move_only_function<int( int )> f3( callable{} );
+        move_only_function<int( int )> f4;
+
+        swap( f3, f4 );
+        BOOST_TEST_NOT( f3 );
+        BOOST_TEST( f4 );
+
+        move_only_function<int( int )> f5;
+        move_only_function<int( int )> f6;
+
+        swap( f5, f6 );
+        BOOST_TEST_NOT( f5 );
+        BOOST_TEST_NOT( f6 );
+    }
+
+    {
+        struct throwing
+        {
+            static int x()
+            {
+                throw 1234;
+            }
+
+            int operator()()
+            {
+                throw 1234;
+            }
+        };
+
+        struct large_throwing
+        {
+            char padding[ 256 ] = {};
+
+            int operator()()
+            {
+                throw 1234;
+            }
+        };
+
+        move_only_function<int()> f1( &throwing::x );
+        move_only_function<int()> f2( throwing{} );
+        move_only_function<int()> f3( large_throwing{} );
+
+        BOOST_TEST_THROWS( f1(), int );
+        BOOST_TEST_THROWS( f2(), int );
+        BOOST_TEST_THROWS( f3(), int );
+    }
+}
+
+struct Q
+{
+    void operator()() const &;
+    void operator()() &&;
+};
+
+struct R
+{
+    void operator()() &;
+    void operator()() &&;
+};
+
+// These types are all small and nothrow move constructible
+struct F { void operator()(); };
+struct G { void operator()() const; };
+
+struct H
+{
+    H( int );
+    H( int, int ) noexcept;
+    void operator()() noexcept;
+};
+
+struct I
+{
+    I( int, const char* );
+    I( std::initializer_list<char> );
+    int operator()() const noexcept;
+};
+
+static void test_traits()
+{
+    // just copy the static assertions from libstdc++'s test suite, call.cc, cons.cc, conv.cc
+
+    // Check return types
+    BOOST_TEST_TRAIT_TRUE( ( is_same<void, invoke_result_t<move_only_function<void()>>> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_same<int, invoke_result_t<move_only_function<int()>>> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_same<int&, invoke_result_t<move_only_function<int&()>>> ) );
+
+    // With const qualifier
+    BOOST_TEST_TRAIT_FALSE( ( is_invocable< move_only_function<void()> const > ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_invocable< move_only_function<void()> const &> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const> > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const> &> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const> const > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const> const &> ) );
+
+    // With no ref-qualifier
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void()> > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void()> &> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const> > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const> &> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const> const > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const> const &> ) );
+
+    // With & ref-qualifier
+    BOOST_TEST_TRAIT_FALSE( ( is_invocable< move_only_function<void()&> > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void()&> &> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const&> > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const&> &> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const&> const > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const&> const &> ) );
+
+    // With && ref-qualifier
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void()&&> > ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_invocable< move_only_function<void()&&> &> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const&&> > ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_invocable< move_only_function<void() const&&> &> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_invocable< move_only_function<void() const&&> const > ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_invocable< move_only_function<void() const&&> const &> ) );
+
+    #if defined(__cpp_noexcept_function_type)
+
+    // With noexcept-specifier
+    BOOST_TEST_TRAIT_FALSE( ( is_nothrow_invocable< move_only_function<void()> > ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_nothrow_invocable< move_only_function<void() noexcept(false)> > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_invocable< move_only_function<void() noexcept> > ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_invocable< move_only_function<void()& noexcept>& > ) );
+
+    #endif
+
+    BOOST_TEST_TRAIT_TRUE( ( std::is_nothrow_default_constructible<move_only_function<void()>> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_constructible<move_only_function<void()>, std::nullptr_t> ) );
+    BOOST_TEST_TRAIT_TRUE( ( std::is_nothrow_move_constructible<move_only_function<void()>> ) );
+    BOOST_TEST_TRAIT_FALSE( ( std::is_copy_constructible<move_only_function<void()>> ) );
+
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, void()> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, void( & )()> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, void( * )()> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, int()> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, int( & )()> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, int( * )()> ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void()>, void( int )> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void(int)>, void( int )> ) );
+
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void( int )>, in_place_type_t<void(*)( int )>, void( int )> ) );
+
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, void() noexcept> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void() noexcept>, void() noexcept> ) );
+
+#if defined(__cpp_noexcept_function_type)
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void() noexcept>, void()> ) );
+#endif
+
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, Q> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void() const>, Q> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void() &>, Q> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void() const &>, Q> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void() &&>, Q> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void() const &&>, Q> ) );
+
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, R> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()&>, R> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()&&>, R> ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void() const>, R> ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void() const&>, R> ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void() const&&>, R> ) );
+
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_constructible<move_only_function<void()>, F> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_constructible<move_only_function<void()>, G> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_constructible<move_only_function<void() const>, G> ) );
+
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_constructible<move_only_function<void()>, H> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_constructible<move_only_function<void() noexcept>, H> ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_nothrow_constructible<move_only_function<void() noexcept >, in_place_type_t<H>, int> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_nothrow_constructible<move_only_function<void() noexcept>, in_place_type_t<H>, int, int> ) );
+
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, in_place_type_t<I>, int, const char*> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_constructible<move_only_function<void()>, in_place_type_t<I>, std::initializer_list<char>> ) );
+
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void()>, move_only_function<void() &>> ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void()>, move_only_function<void() &&>> ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void()&>, move_only_function<void() &&>> ) );
+    BOOST_TEST_TRAIT_FALSE( ( is_constructible<move_only_function<void() const>, move_only_function<void()>> ) );
+
+    using FuncType = int( int );
+
+    // Top level const qualifiers are ignored in function types, and decay
+    // is performed.
+    BOOST_TEST_TRAIT_TRUE( ( is_same<move_only_function<void( int const )>, move_only_function<void( int )>> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_same<move_only_function<void( int[ 2 ] )>, move_only_function<void( int* )>> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_same<move_only_function<void( int[] )>, move_only_function<void( int* )>> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_same<move_only_function<void(int const[ 5 ])>, move_only_function<void( int const* )>> ) );
+    BOOST_TEST_TRAIT_TRUE( ( is_same<move_only_function<void( FuncType )>, move_only_function<void( FuncType* )>> ) );
+}
+
+static void test_conv()
+{
+    {
+        noex_callable nt;
+
+        move_only_function<int( int ) noexcept> f1( std::move( nt ) );
+        move_only_function<int( int )> f2( std::move( f1 ) );
+        BOOST_TEST_EQ( f2( 1234 ), 1235 );
+    }
+
+    {
+        auto l = []( noex_callable const& c ) noexcept { return *c.p_ + 1234; };
+
+        noex_callable c;
+
+        move_only_function<int( noex_callable ) const noexcept> f1( l );
+        BOOST_TEST_EQ( f1( c ), 1235 );
+
+        move_only_function<int( noex_callable ) const> f2( std::move( f1 ) );
+        BOOST_TEST_EQ( f2( c ), 1235 );
+
+        move_only_function<int( noex_callable )> f3( std::move( f2 ) );
+        BOOST_TEST_EQ( f3( c ), 1235 );
+
+        move_only_function<int( noex_callable&& )> f4( std::move( f3 ) );
+        BOOST_TEST_EQ( f4( noex_callable{} ), 1235 );
+
+        move_only_function<int( noex_callable&& ) &&> f5( std::move( f4 ) );
+        BOOST_TEST_EQ( std::move( f5 )( noex_callable{} ), 1235 );
+
+        move_only_function<int( noex_callable&& )> f6( l );
+
+        move_only_function<int( noex_callable&& ) &> f7( std::move( f6 ) );
+        BOOST_TEST_EQ( f7( noex_callable{} ), 1235 );
+
+        // TODO: libstdc++ includes this test case but it seems like pedantically calling a `long(*)(Arg)` should
+        // be UB in the general sense. We need to confirm one way or another if this is something we need to support.
+        //
+        // move_only_function<int( noex_callable ) const noexcept> f8( l );
+        // move_only_function<long( noex_callable ) const noexcept> f9( std::move( f8 ) );
+        // BOOST_TEST_EQ( f9( noex_callable{} ), 1235 );
+    }
+
+    {
+        move_only_function<int( long ) const noexcept> e;
+        BOOST_TEST( e == nullptr );
+
+        move_only_function<int( long ) const> e2( std::move( e ) );
+        BOOST_TEST( e2 == nullptr );
+        e2 = std::move( e );
+        BOOST_TEST( e2 == nullptr );
+
+        move_only_function<int( long )> e3( std::move( e2 ) );
+        BOOST_TEST( e3 == nullptr );
+    }
+}
+
+int main()
+{
+    test_call();
+    test_traits();
+    test_conv();
+
+    return boost::report_errors();
+}
--- a/test/nontype_test.cpp
+++ b/test/nontype_test.cpp
@@ -0,0 +1,33 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/compat/detail/nontype.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !( defined(__cpp_nontype_template_parameter_auto) && __cpp_nontype_template_parameter_auto >= 201606L )
+
+BOOST_PRAGMA_MESSAGE("Test skipped, __cpp_nontype_template_parameter_auto is not defined to at least 201606L")
+int main() {}
+
+#else
+
+void f() {}
+
+struct X
+{
+    void f() {}
+};
+
+int main()
+{
+    BOOST_TEST_TRAIT_SAME( boost::compat::nontype_t< 5 > const, decltype( boost::compat::nontype< 5 > ) );
+    BOOST_TEST_TRAIT_SAME( boost::compat::nontype_t< ::f > const, decltype( boost::compat::nontype< ::f > ) );
+    BOOST_TEST_TRAIT_SAME( boost::compat::nontype_t< &X::f > const, decltype( boost::compat::nontype< &X::f > ) );
+
+    return boost::report_errors();
+}
+
+#endif
--- a/test/to_underlying_test.cpp
+++ b/test/to_underlying_test.cpp
@@ -0,0 +1,75 @@
+// Copyright 2025 Braden Ganetsky
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/compat/to_underlying.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <cstdint>
+
+enum unscoped
+{
+    unscoped_value = 1
+};
+
+enum unscoped_int8_t : std::int8_t
+{
+    unscoped_int8_t_value = 2
+};
+
+enum unscoped_uint16_t : std::uint16_t
+{
+    unscoped_uint16_t_value = 3
+};
+
+enum class scoped
+{
+    value = 4
+};
+
+enum class scoped_int8_t : std::int8_t
+{
+    value = 5
+};
+
+enum class scoped_uint16_t : std::uint16_t
+{
+    value = 6
+};
+
+int main()
+{
+    {
+        auto output = boost::compat::to_underlying(unscoped_value);
+        // Per the standard [dcl.enum], the underlying type of an unscoped enumeration
+        // is unspecified, unless it is explicitly specified.
+        BOOST_TEST_EQ(output, 1);
+    }
+    {
+        auto output = boost::compat::to_underlying(unscoped_int8_t_value);
+        BOOST_TEST_TRAIT_SAME(decltype(output), std::int8_t);
+        BOOST_TEST_EQ(output, 2);
+    }
+    {
+        auto output = boost::compat::to_underlying(unscoped_uint16_t_value);
+        BOOST_TEST_TRAIT_SAME(decltype(output), std::uint16_t);
+        BOOST_TEST_EQ(output, 3);
+    }
+    {
+        auto output = boost::compat::to_underlying(scoped::value);
+        BOOST_TEST_TRAIT_SAME(decltype(output), int);
+        BOOST_TEST_EQ(output, 4);
+    }
+    {
+        auto output = boost::compat::to_underlying(scoped_int8_t::value);
+        BOOST_TEST_TRAIT_SAME(decltype(output), std::int8_t);
+        BOOST_TEST_EQ(output, 5);
+    }
+    {
+        auto output = boost::compat::to_underlying(scoped_uint16_t::value);
+        BOOST_TEST_TRAIT_SAME(decltype(output), std::uint16_t);
+        BOOST_TEST_EQ(output, 6);
+    }
+
+    return boost::report_errors();
+}
Author	SHA1	Message	Date
Peter Dimov	7ce75ac955	Update ci.yml	2026-01-16 02:16:52 +02:00
Peter Dimov	0776d62a95	Update documentation	2025-11-18 14:33:45 +02:00
Peter Dimov	904b80b8a1	Move nontype.hpp to detail	2025-11-18 14:33:45 +02:00
Peter Dimov	ffaadc079d	Update .drone.jsonnet	2025-11-18 12:06:25 +02:00
Peter Dimov	ab09450342	Update documentation of function_ref	2025-11-03 18:54:47 +02:00
Peter Dimov	79ca9646ea	Update documentation of nontype to clarify that it requires C++17	2025-11-03 18:41:18 +02:00
Peter Dimov	6b9e52c284	Rename detail::nontype11 to nttp_holder	2025-11-01 19:45:39 +02:00
Peter Dimov	4c9e9079c1	Remove feature check for variable templates; if we have auto template parameters (C++17) we probably have C++14 as well	2025-11-01 19:32:34 +02:00
Peter Dimov	e522245e9c	Remove uses of is_rvalue_reference_v	2025-11-01 19:21:51 +02:00
Peter Dimov	cef4d529d0	Remove BOOST_COMPAT_HAS_AUTO_NTTP	2025-11-01 19:16:17 +02:00
Peter Dimov	1e3cb9cc7a	Disable tests that require noexcept function types to pass	2025-11-01 19:15:14 +02:00
Peter Dimov	1226bab251	Remove use of BOOST_COMPAT_HAS_AUTO_NTTP in function_ref_mfn_noexcept_test.cpp	2025-11-01 19:00:44 +02:00
Peter Dimov	f9dd6181fb	Remove use of BOOST_COMPAT_HAS_AUTO_NTTP in function_ref_mfn_test.cpp	2025-11-01 18:51:37 +02:00
Peter Dimov	db39b5075c	Add a C++11 compatible base class to nontype_t; unconditionally enable the function_ref constructors for it	2025-11-01 18:36:05 +02:00
Peter Dimov	f72aeb4e59	Update documentation	2025-11-01 17:57:22 +02:00
Peter Dimov	8e7e16e9c3	Add nontype_test.cpp	2025-11-01 17:18:55 +02:00
Peter Dimov	f897f32064	Extract nontype_t to its own header; add nontype	2025-11-01 17:07:54 +02:00
Peter Dimov	a5a56ee5c0	Merge pull request #22 from k3DW/to_underlying Add `to_underlying`	2025-09-05 18:48:05 +03:00
Braden Ganetsky	72ff680a72	Fix function signature in to_array docs	2025-09-05 09:33:40 -05:00
Braden Ganetsky	94b1675762	Add to_underlying	2025-09-05 09:33:40 -05:00
Peter Dimov	694b78df7a	Update ci.yml	2025-09-04 16:08:07 +03:00
Peter Dimov	e374640265	Remove windows-2019 from ci.yml	2025-07-02 19:06:07 +03:00
Christian Mazakas	f496e814b5	update changelog	2025-07-02 07:12:23 -07:00
Peter Dimov	10e1dad9ba	Merge pull request #21 from cmazakas/feature/move-only-function add move_only_function	2025-06-28 17:52:06 +03:00
Christian Mazakas	6172b5e50f	add move_only_function docs	2025-06-11 19:57:40 -07:00
Christian Mazakas	1a60e0357c	add move_only_function	2025-06-11 19:57:30 -07:00
Christian Mazakas	6901952904	remove ubuntu 20 from posix cmake gha jobs	2025-05-29 15:26:16 -07:00
Christian Mazakas	a1eb40bd0e	update gha to use containers	2025-05-29 15:26:16 -07:00
Christian Mazakas	61b464c3ee	Merge pull request #17 from cmazakas/fix/lvalue-params fix lvalue parameter passing	2024-12-17 12:49:24 -08:00
Christian Mazakas	c3bd40856d	remove erroneous rvalue qualification	2024-12-17 11:20:57 -08:00
Christian Mazakas	736b381d13	add failing test case Passing an lvalue ref parameter when arguments are by-value causes a failure of reference binding.	2024-12-17 11:20:18 -08:00
Peter Dimov	881cc909fb	Update .drone.jsonnet	2024-12-13 03:55:39 +02:00
Peter Dimov	c9f3354cff	Apply Node20 workaround	2024-12-13 03:34:16 +02:00
Peter Dimov	c4924db9e5	Update ci.yml	2024-12-13 03:21:42 +02:00