⬆️ Update to C++23

Problem:
- C++23 is supported by our required toolchains, but we are not taking advantage of it.

Solution:
- Update to C++23.

Note:
- The `cpp20` branch will be created from `main`. C++20 is still supported on that branch.
- Upgrading to C++23 on `main` also means that clang-18 is now the earliest supported clang toolchain.

Author: elbeno

.github/workflows/unit_tests.yml

@@ -12,7 +12,7 @@ on:
 env:
   DEBIAN_FRONTEND: noninteractive
   CMAKE_GENERATOR: Ninja
-  DEFAULT_CXX_STANDARD: 20
+  DEFAULT_CXX_STANDARD: 23
   DEFAULT_LLVM_VERSION: 21
   DEFAULT_GCC_VERSION: 14
   MULL_LLVM_MAJOR_VERSION: 19
@@ -31,8 +31,8 @@ jobs:
       fail-fast: false
       matrix:
         compiler: [clang, gcc]
-        version: [12, 13, 14, 16, 17, 18, 19, 20, 21]
-        cxx_standard: [17, 20]
+        version: [12, 13, 14, 18, 19, 20, 21]
+        cxx_standard: [23]
         stdlib: [libstdc++, libc++]
         build_type: [Debug]
         include:
@@ -76,24 +76,6 @@ jobs:
             stdlib: libc++
             install: sudo apt update && sudo apt install -y clang-18 libc++-18-dev libc++abi-18-dev
             cxx_flags: "-stdlib=libc++"
-          - version: 17
-            compiler: clang
-            install: sudo apt update && sudo apt install -y clang-17
-            toolchain_root: "/usr/lib/llvm-17"
-          - version: 17
-            compiler: clang
-            stdlib: libc++
-            install: sudo apt update && sudo apt install -y clang-17 libc++-17-dev libc++abi-17-dev
-            cxx_flags: "-stdlib=libc++"
-          - version: 16
-            compiler: clang
-            install: sudo apt update && sudo apt install -y clang-16
-            toolchain_root: "/usr/lib/llvm-16"
-          - version: 16
-            compiler: clang
-            stdlib: libc++
-            install: sudo apt update && sudo apt install -y clang-16 libc++-16-dev libc++abi-16-dev
-            cxx_flags: "-stdlib=libc++"
           - compiler: gcc
             toolchain_root: "/usr"
             cxx_flags: ""
@@ -122,10 +104,6 @@ jobs:
             version: 19
           - compiler: gcc
             version: 18
-          - compiler: gcc
-            version: 17
-          - compiler: gcc
-            version: 16
           - compiler: clang
             version: 14
           - compiler: clang
@@ -183,92 +161,6 @@ jobs:
         working-directory: ${{github.workspace}}/build
         run: ctest --output-on-failure -j $(nproc) -C ${{matrix.build_type}}
 
-  build_and_test_22:
-    runs-on: ${{ github.repository_owner == 'intel' && 'intel-' || '' }}ubuntu-22.04
-    strategy:
-      fail-fast: false
-      matrix:
-        compiler: [clang]
-        version: [14, 15]
-        cxx_standard: [17, 20]
-        stdlib: [libstdc++, libc++]
-        build_type: [Debug]
-        include:
-          - compiler: clang
-            cc: "clang"
-            cxx: "clang++"
-            cxx_flags: "-stdlib=libstdc++"
-          - version: 15
-            compiler: clang
-            install: sudo apt update && sudo apt install -y clang-15
-            toolchain_root: "/usr/lib/llvm-15"
-          - version: 15
-            compiler: clang
-            stdlib: libc++
-            install: sudo apt update && sudo apt install -y clang-15 libc++-15-dev libc++abi-15-dev
-            cxx_flags: "-stdlib=libc++"
-          - version: 14
-            compiler: clang
-            install: sudo apt update && sudo apt install -y clang-14
-            toolchain_root: "/usr/lib/llvm-14"
-          - version: 14
-            compiler: clang
-            stdlib: libc++
-            install: sudo apt update && sudo apt install -y clang-14 libc++-14-dev libc++abi-14-dev
-            cxx_flags: "-stdlib=libc++"
-        exclude:
-          - compiler: clang
-            version: 14
-            stdlib: libstdc++
-
-    steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      - name: Install build tools
-        run: |
-          ${{ matrix.install }}
-          sudo apt install -y ninja-build python3-venv python3-pip
-
-      - name: Restore CPM cache
-        env:
-          cache-name: cpm-cache-0
-        id: cpm-cache-restore
-        uses: actions/cache/restore@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-        with:
-          path: ~/cpm-cache
-          key: ${{runner.os}}-${{env.cache-name}}-${{ hashFiles('**/CMakeLists.txt', 'cmake/**') }}
-          restore-keys: |
-            ${{runner.os}}-${{env.cache-name}}-
-
-      - name: Configure CMake
-        env:
-          CC: ${{matrix.toolchain_root}}/bin/${{matrix.cc}}
-          CXX: ${{matrix.toolchain_root}}/bin/${{matrix.cxx}}
-        run: cmake -B ${{github.workspace}}/build -DCMAKE_CXX_STANDARD=${{matrix.cxx_standard}} -DCMAKE_CXX_FLAGS_INIT=${{matrix.cxx_flags}} -DCMAKE_BUILD_TYPE=${{matrix.build_type}} -DCPM_SOURCE_CACHE=~/cpm-cache
-
-      - name: Save CPM cache
-        env:
-          cache-name: cpm-cache-0
-        if: steps.cpm-cache-restore.outputs.cache-hit != 'true'
-        uses: actions/cache/save@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
-        with:
-          path: ~/cpm-cache
-          key: ${{runner.os}}-${{env.cache-name}}-${{ hashFiles('**/CMakeLists.txt', 'cmake/**') }}
-
-      - name: Install python test requirements
-        run: |
-          python3 -m venv ${{github.workspace}}/test_venv
-          source ${{github.workspace}}/test_venv/bin/activate
-          pip install -r ${{github.workspace}}/requirements.txt
-          echo "${{github.workspace}}/test_venv/bin" >> $GITHUB_PATH
-
-      - name: Build Unit Tests
-        run: cmake --build ${{github.workspace}}/build --config ${{matrix.build_type}} -v -t build_unit_tests
-
-      - name: Test
-        working-directory: ${{github.workspace}}/build
-        run: ctest --output-on-failure -j $(nproc) -C ${{matrix.build_type}}
-
   quality_checks_pass:
     runs-on: ${{ github.repository_owner == 'intel' && 'intel-' || '' }}ubuntu-24.04
     steps:
@@ -530,7 +422,7 @@ jobs:
 
   merge_ok:
     runs-on: ${{ github.repository_owner == 'intel' && 'intel-' || '' }}ubuntu-24.04
-    needs: [build_and_test_24, build_and_test_22, mutate, quality_checks_pass, sanitize, valgrind]
+    needs: [build_and_test_24, mutate, quality_checks_pass, sanitize, valgrind]
     if: ${{ !cancelled() }}
     steps:
       - name: Enable merge

.github/workflows/usage_test.yml

@@ -16,7 +16,7 @@ env:
 
 jobs:
   usage_test:
-    runs-on: ${{ github.repository_owner == 'intel' && 'intel-' || '' }}ubuntu-22.04
+    runs-on: ${{ github.repository_owner == 'intel' && 'intel-' || '' }}ubuntu-24.04
     strategy:
       fail-fast: false
       matrix:
@@ -26,8 +26,8 @@ jobs:
           - compiler: clang
             cc: "clang"
             cxx: "clang++"
-            install: sudo apt update && sudo apt install -y clang-14
-            toolchain_root: "/usr/lib/llvm-14"
+            install: sudo apt update && sudo apt install -y clang-18
+            toolchain_root: "/usr/lib/llvm-18"
           - compiler: gcc
             cc: "gcc-12"
             cxx: "g++-12"
@@ -44,16 +44,17 @@ jobs:
 
       - name: Install cmake
         run: |
-          pip3 install --upgrade pip
-          pip3 install --force cmake==${{env.USER_CMAKE_VERSION}}
+          python3 -m venv ${{github.workspace}}/test_venv
+          source ${{github.workspace}}/test_venv/bin/activate
+          pip install cmake==${{env.USER_CMAKE_VERSION}}
 
-      - name: Configure CMake
+      - name: Configure cmake
         env:
           CC: ${{matrix.toolchain_root}}/bin/${{matrix.cc}}
           CXX: ${{matrix.toolchain_root}}/bin/${{matrix.cxx}}
         working-directory: ${{github.workspace}}/usage_test
-        run: ~/.local/bin/cmake -B build -DCPP_IMPLEMENTATION=${{matrix.cpp_implementation}}
+        run: ${{github.workspace}}/test_venv/bin/cmake -B build -DCPP_IMPLEMENTATION=${{matrix.cpp_implementation}}
 
       - name: Build
         working-directory: ${{github.workspace}}/usage_test
-        run: ~/.local/bin/cmake --build build
+        run: ${{github.workspace}}/test_venv/bin/cmake --build build

CMakeLists.txt

@@ -15,11 +15,11 @@ else()
 endif()
 
 add_versioned_package("gh:boostorg/mp11#boost-1.83.0")
-fmt_recipe(11.1.3)
+fmt_recipe(12.1.0)
 add_versioned_package("gh:intel/cpp-baremetal-concurrency#06e5901")
 
 if(NOT DEFINED CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 20)
+    set(CMAKE_CXX_STANDARD 23)
 endif()
 
 add_library(stdx INTERFACE)

README.md

@@ -4,14 +4,21 @@
 
  *stdx* is a C++ header-only library that:
 
-- backports to C++17 some standard library features from C++20 and beyond
+- backports to C++N some standard library features from C++(>N) and beyond
 - adds some useful extra utilities that are missing from the standard
- 
-Some of the extras are available only with C++20 or later.
- 
-*stdx* supports:
- 
-- clang 14 through 21
-- gcc 12 through 14
 
 See the [full documentation](https://intel.github.io/cpp-std-extensions/).
+
+C++ standard support is as follows:
+
+- C++23: [main branch](https://github.com/intel/cpp-std-extensions/tree/main) (active development)
+- C++20: [cpp20 branch](https://github.com/intel/cpp-std-extensions/tree/main) (supported)
+- C++17: unsupported, but many features in the [cpp20 branch](https://github.com/intel/cpp-std-extensions/tree/cpp20) will work with C++17 also.
+
+Compiler support:
+
+| Branch | GCC versions | Clang versions |
+| --- | --- | --- |
+| [main](https://github.com/intel/cpp-baremetal-concurrency/tree/main) | 12 thru 14 | 18 thru 21 |
+| [cpp20](https://github.com/intel/cpp-baremetal-concurrency/tree/cpp20) | 12 thru 14 | 14 thru 21 |
+

include/stdx/functional.hpp

@@ -1,18 +1,11 @@
 #pragma once
 
+#include <stdx/tuple.hpp>
 #include <stdx/type_traits.hpp>
 
 #include <functional>
 #include <type_traits>
 
-#if __cpp_lib_bind_front < 202306L or __cpp_lib_bind_back < 202306L
-#if __cplusplus >= 202002L
-#include <stdx/tuple.hpp>
-#else
-#include <tuple>
-#endif
-#endif
-
 namespace stdx {
 inline namespace v1 {
 
@@ -34,20 +27,10 @@ template <typename F> with_result_of(F) -> with_result_of<F>;
 #endif
 
 namespace detail {
-#if __cpp_lib_bind_front < 202306L or __cpp_lib_bind_back < 202306L
-#if __cplusplus >= 202002L
 template <typename... Ts> using bind_tuple_t = stdx::tuple<Ts...>;
 using stdx::get;
-#else
-template <typename... Ts> using bind_tuple_t = std::tuple<Ts...>;
-using std::get;
-#endif
-#endif
 } // namespace detail
 
-#if __cpp_lib_bind_front >= 201907L
-using std::bind_front;
-#else
 namespace detail {
 template <typename...> struct bind_front_t;
 
@@ -77,9 +60,7 @@ constexpr auto bind_front(F &&f, Args &&...args) {
                                 std::decay_t<Args>...>{
         std::forward<F>(f), {std::forward<Args>(args)...}};
 }
-#endif
 
-#if __cpp_lib_bind_front < 202306L
 namespace detail {
 template <auto, typename...> struct bind_front_value_t;
 
@@ -106,11 +87,6 @@ template <auto F, typename... Args> constexpr auto bind_front(Args &&...args) {
         {std::forward<Args>(args)...}};
 }
 
-#endif
-
-#if __cpp_lib_bind_back >= 202202L
-using std::bind_back;
-#else
 namespace detail {
 template <typename...> struct bind_back_t;
 
@@ -140,9 +116,7 @@ constexpr auto bind_back(F &&f, Args &&...args) {
                                std::decay_t<Args>...>{
         std::forward<F>(f), {std::forward<Args>(args)...}};
 }
-#endif
 
-#if __cpp_lib_bind_back < 202306L
 namespace detail {
 template <auto, typename...> struct bind_back_value_t;
 
@@ -169,8 +143,6 @@ template <auto F, typename... Args> constexpr auto bind_back(Args &&...args) {
         {std::forward<Args>(args)...}};
 }
 
-#endif
-
 // NOLINTBEGIN(modernize-use-constraints)
 template <typename T = void> struct unary_plus {
     template <typename U,

include/stdx/utility.hpp

@@ -104,7 +104,6 @@ constexpr static auto reverse_value_lookup_v =
                   expand<M>())),
               detail::value_t<Default>>::value;
 
-#if __cpp_lib_forward_like < 202207L
 template <typename T, typename U>
 [[nodiscard]] constexpr auto forward_like(U &&u) noexcept -> decltype(auto) {
     constexpr auto t_is_const = std::is_const_v<std::remove_reference_t<T>>;
@@ -113,7 +112,7 @@ template <typename T, typename U>
         if constexpr (t_is_const) {
             return std::as_const(u);
         } else {
-            return (u);
+            return static_cast<U &>(u);
         }
     } else {
         if constexpr (t_is_const) {
@@ -123,11 +122,9 @@ template <typename T, typename U>
         }
     }
 }
-#else
-using std::forward_like;
-#endif
+
 template <typename T, typename U>
-using forward_like_t = decltype(forward_like<T>(std::declval<U>()));
+using forward_like_t = decltype(stdx::forward_like<T>(std::declval<U>()));
 
 template <typename T, std::enable_if_t<std::is_integral_v<T>, int> = 0>
 [[nodiscard]] constexpr auto as_unsigned(T t) {