Add fmt library integration example

.github/workflows/ci.yml

@@ -58,6 +58,9 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
+      - name: Install {fmt}
+        run: sudo apt install libfmt-dev
+
       - name: Install packages
         if: matrix.install
         run: sudo apt install ${{matrix.install}}
@@ -151,6 +154,15 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
+      - uses: microsoft/setup-msbuild@v1.1
+      - name: Install {fmt}
+        uses: lukka/run-vcpkg@v6
+        with:
+          vcpkgGitCommitId: '88b1071e39f13b632644d9d953738d345a4ac055'
+          vcpkgDirectory: '${{ runner.workspace }}/vcpkg'
+          vcpkgTriplet: x64-windows
+          vcpkgArguments: fmt
+
       - name: Setup Boost
         shell: cmd
         run: |

example/fmtlib_formatter.cpp

@@ -0,0 +1,70 @@
+// Copyright (c) 2023 Denis Mikhailov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/pfr.hpp>
+#include <fmt/format.h>
+#include <type_traits>
+
+namespace boost::pfr {
+    struct fmtlib_tag;
+}
+
+template<class T> struct fmt::formatter<T, char, std::enable_if_t<
+    boost::pfr::is_reflectable<T, boost::pfr::fmtlib_tag>::value>>
+{
+    constexpr auto parse(format_parse_context& ctx) -> format_parse_context::iterator {
+        auto it = ctx.begin(), end = ctx.end();
+
+        if (it != end && *it != '}') ctx.error_handler().on_error( "invalid format" );
+
+        return it;
+    }
+
+    auto format(const T& t, format_context& ctx) const -> format_context::iterator {
+        using namespace boost::pfr;
+
+        auto out = ctx.out();
+
+        *out++ = '{';
+
+        const char* div = "";
+        constexpr auto names = names_as_array<T>();
+
+        for_each_field(t, [&](const auto& field, auto I) {
+            out = fmt::format_to(out, "{}", std::exchange(div, ","));
+            out = fmt::format_to(out, " .{}={}", names[I], field);
+            });
+
+        out = fmt::format_to(out, "{}", std::strlen(div) == 0 ? "}" : " }");
+
+        return out;
+    }
+};
+
+struct point
+{
+    int x, y;
+};
+
+struct color
+{
+    unsigned char r, g, b;
+};
+
+struct line
+{
+    color clr;
+    point first, last;
+};
+
+template<> struct boost::pfr::is_reflectable<point, boost::pfr::fmtlib_tag> : std::integral_constant<bool, true> {};
+template<> struct boost::pfr::is_reflectable<color, boost::pfr::fmtlib_tag> : std::integral_constant<bool, true> {};
+template<> struct boost::pfr::is_reflectable<line, boost::pfr::fmtlib_tag> : std::integral_constant<bool, true> {};
+
+int main()
+{
+    fmt::print("{}\n", line{ { 255, 192, 16 }, { 1, 2 }, { 3, 4 } });
+}
+

test/appveyor.yml

@@ -69,7 +69,19 @@ environment:
       TOOLSET: gcc
       CXXSTD: 14,1z
 
+cache:
+  - c:\tools\vcpkg\installed\
+
 before_build:
+      # Install {fmt} library in order to run examples
+    # FIXME: To be removed https://help.appveyor.com/discussions/problems/13000-cmake_toolchain_filevcpkgcmake-conflicts-with-cmake-native-findboostcmake"
+    - ps: 'Write-Host "Installing latest vcpkg.cmake module" -ForegroundColor Magenta'
+    - appveyor DownloadFile https://raw.githubusercontent.com/Microsoft/vcpkg/master/scripts/buildsystems/vcpkg.cmake -FileName "c:\tools\vcpkg\scripts\buildsystems\vcpkg.cmake"
+    - set "TRIPLET=x64-windows"
+    - vcpkg --triplet %TRIPLET% install fmt
+    - set PATH=C:\Tools\vcpkg\installed\%TRIPLET%\bin;%PATH%
+    - set VCPKG_I=C:\Tools\vcpkg\installed\%TRIPLET%\include
+    - set VCPKG_L=C:\Tools\vcpkg\installed\%TRIPLET%\lib
     - set BOOST_BRANCH=develop
     - if "%APPVEYOR_REPO_BRANCH%" == "master" set BOOST_BRANCH=master
     - echo "Testing %BOOST_LIBS_FOLDER%"
@@ -85,6 +97,17 @@ before_build:
     - python tools/boostdep/depinst/depinst.py --git_args "--depth 10 --jobs 2" -I example -I examples %BOOST_LIBS_FOLDER%
 
 build_script:
+    - xcopy %APPVEYOR_BUILD_FOLDER%\fmt.jam %USERPROFILE%
+    - ps: |
+        # Creating %USERPROFILE%/user-config.jam file
+        @'
+        import os regex toolset ;
+        local toolset = [ regex.split [ os.environ TOOLSET ] "-" ] ;
+        local vcpkg_i = [ os.environ VCPKG_I ] ;
+        local vcpkg_l = [ os.environ VCPKG_L ] ;
+        using $(toolset[1]) : $(toolset[2-]:J="-") : ;
+        using fmt : : <include>$(vcpkg_i) <search>$(vcpkg_l) ;
+        '@ | sc "$env:USERPROFILE/user-config.jam"
     - cmd /c bootstrap
     - b2.exe headers
     - cd %BOOST%/libs/%BOOST_LIBS_FOLDER%/test