Do not use <shared_mutex> when BOOST_USE_WINAPI_VERSION is 0x5xx (Windows XP). Fixes #113.

Closes #108.

.github/workflows/ci.yml

@@ -55,6 +55,11 @@ jobs:
             cxxstd: "03,11,14,17,20,2b"
             os: ubuntu-22.04
             install: g++-12
+          - toolset: gcc-13
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-latest
+            container: ubuntu:23.04
+            install: g++-13
           - toolset: clang
             compiler: clang++-3.9
             cxxstd: "03,11,14"
@@ -115,12 +120,26 @@ jobs:
             cxxstd: "03,11,14,17,20,2b"
             os: ubuntu-22.04
             install: clang-14
+          - toolset: clang
+            compiler: clang++-15
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-22.04
+            install: clang-15
+          - toolset: clang
+            compiler: clang++-16
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-latest
+            container: ubuntu:23.04
+            install: clang-16
           - toolset: clang
             cxxstd: "03,11,14,17,2a"
             os: macos-11
           - toolset: clang
-            cxxstd: "03,11,14,17,2a"
+            cxxstd: "03,11,14,17,20,2b"
             os: macos-12
+          - toolset: clang
+            cxxstd: "03,11,14,17,20,2b"
+            os: macos-13
 
     runs-on: ${{matrix.os}}
     container: ${{matrix.container}}
@@ -136,11 +155,13 @@ jobs:
         if: matrix.container
         run: |
           apt-get update
-          apt-get -y install sudo python git g++
+          apt-get -y install sudo python3 git g++
 
       - name: Install packages
         if: matrix.install
-        run: sudo apt-get -y install ${{matrix.install}}
+        run: |
+          sudo apt-get update
+          sudo apt-get -y install ${{matrix.install}}
 
       - name: Setup Boost
         run: |
@@ -160,7 +181,7 @@ jobs:
           cd boost-root
           cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
           git submodule update --init tools/boostdep
-          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+          python3 tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
           ./bootstrap.sh
           ./b2 -d0 headers
 
@@ -242,6 +263,7 @@ jobs:
           - os: ubuntu-22.04
           - os: macos-11
           - os: macos-12
+          - os: macos-13
 
     runs-on: ${{matrix.os}}
 
@@ -289,6 +311,7 @@ jobs:
           - os: ubuntu-22.04
           - os: macos-11
           - os: macos-12
+          - os: macos-13
 
     runs-on: ${{matrix.os}}
 
@@ -346,6 +369,7 @@ jobs:
           - os: ubuntu-22.04
           - os: macos-11
           - os: macos-12
+          - os: macos-13
 
     runs-on: ${{matrix.os}}
 
@@ -391,3 +415,183 @@ jobs:
         run: |
           cd ../boost-root/__build__
           ctest --output-on-failure --no-tests=error
+
+  windows-cmake-subdir:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Use library with add_subdirectory (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_subdir_test
+          mkdir __build__ && cd __build__
+          cmake ..
+          cmake --build . --config Debug
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Use library with add_subdirectory (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_subdir_test/__build__
+          cmake --build . --config Release
+          ctest --output-on-failure --no-tests=error -C Release
+
+  windows-cmake-install:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Configure
+        shell: cmd
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=%LIBRARY% -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+
+      - name: Install (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install --config Debug
+
+      - name: Install (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install --config Release
+
+      - name: Use the installed library (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_install_test && mkdir __build__ && cd __build__
+          cmake -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+          cmake --build . --config Debug
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Use the installed library (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_install_test/__build__
+          cmake --build . --config Release
+          ctest --output-on-failure --no-tests=error -C Release
+
+  windows-cmake-test:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Configure
+        shell: cmd
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=%LIBRARY% -DBUILD_TESTING=ON ..
+
+      - name: Build tests (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests --config Debug
+
+      - name: Run tests (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Build tests (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests --config Release
+
+      - name: Run tests (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error -C Release

doc/system/reference.adoc

@@ -1657,7 +1657,8 @@ public:
 
     // error access
 
-    constexpr E error() const;
+    constexpr E error() const &;
+    constexpr E error() &&;
 
     // emplace
 
@@ -1851,7 +1852,8 @@ Returns: ::
 #### Error Access
 
 ```
-constexpr E error() const;
+constexpr E error() const &;
+constexpr E error() &&;
 ```
 [none]
 * {blank}
@@ -1979,7 +1981,8 @@ public:
 
     // error access
 
-    constexpr E error() const;
+    constexpr E error() const &;
+    constexpr E error() &&;
 
     // emplace
 
@@ -2120,7 +2123,8 @@ Effects: ::
 #### Error Access
 
 ```
-constexpr E error() const;
+constexpr E error() const &;
+constexpr E error() &&;
 ```
 [none]
 * {blank}

include/boost/system/detail/config.hpp

@@ -8,6 +8,7 @@
 //
 // See http://www.boost.org/libs/system for documentation.
 
+#include <boost/system/detail/requires_cxx11.hpp>
 #include <boost/config.hpp>
 #include <boost/config/workaround.hpp>
 

include/boost/system/detail/error_category.hpp

@@ -13,6 +13,7 @@
 #include <boost/system/detail/config.hpp>
 #include <boost/cstdint.hpp>
 #include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 #include <string>
 #include <functional>
 #include <cstddef>
@@ -116,11 +117,18 @@ protected:
 
 #endif
 
-    BOOST_SYSTEM_CONSTEXPR error_category() BOOST_NOEXCEPT: id_( 0 ), stdcat_(), sc_init_()
+#if !BOOST_WORKAROUND(BOOST_GCC, < 40800)
+    BOOST_CONSTEXPR
+#endif
+    error_category() BOOST_NOEXCEPT: id_( 0 ), stdcat_(), sc_init_()
     {
     }
 
-    explicit BOOST_SYSTEM_CONSTEXPR error_category( boost::ulong_long_type id ) BOOST_NOEXCEPT: id_( id ), stdcat_(), sc_init_()
+    explicit
+#if !BOOST_WORKAROUND(BOOST_GCC, < 40800)
+    BOOST_CONSTEXPR
+#endif
+    error_category( boost::ulong_long_type id ) BOOST_NOEXCEPT: id_( id ), stdcat_(), sc_init_()
     {
     }
 

include/boost/system/detail/mutex.hpp

@@ -31,15 +31,32 @@ struct mutex
 } // namespace system
 } // namespace boost
 
-#elif defined(BOOST_MSSTL_VERSION) && BOOST_MSSTL_VERSION >= 140
+#else // defined(BOOST_SYSTEM_DISABLE_THREADS)
+
+#if defined(BOOST_MSSTL_VERSION) && BOOST_MSSTL_VERSION >= 140
 
 // Under the MS STL, std::mutex::mutex() is not constexpr, as is
 // required by the standard, which leads to initialization order
 // issues. However, shared_mutex is based on SRWLock and its
 // default constructor is constexpr, so we use that instead.
 
+#include <boost/winapi/config.hpp>
+
+// SRWLOCK is not available when targeting Windows XP
+#if BOOST_USE_WINAPI_VERSION >= BOOST_WINAPI_VERSION_WIN6
+
 #include <shared_mutex>
 
+#if BOOST_MSSTL_VERSION >= 142 || _HAS_SHARED_MUTEX
+# define BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX
+#endif
+
+#endif // BOOST_MSSTL_VERSION >= 142 || _HAS_SHARED_MUTEX
+
+#endif // BOOST_USE_WINAPI_VERSION >= BOOST_WINAPI_VERSION_WIN6
+
+#if defined(BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX)
+
 namespace boost
 {
 namespace system
@@ -53,7 +70,7 @@ typedef std::shared_mutex mutex;
 } // namespace system
 } // namespace boost
 
-#else
+#else // defined(BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX)
 
 #include <mutex>
 
@@ -70,7 +87,8 @@ using std::mutex;
 } // namespace system
 } // namespace boost
 
-#endif
+#endif // defined(BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX)
+#endif // defined(BOOST_SYSTEM_DISABLE_THREADS)
 
 namespace boost
 {

include/boost/system/detail/requires_cxx11.hpp

@@ -0,0 +1,21 @@
+#ifndef BOOST_SYSTEM_DETAIL_REQUIRES_CXX11_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_REQUIRES_CXX11_HPP_INCLUDED
+
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX11_CONSTEXPR) || \
+    defined(BOOST_NO_CXX11_NOEXCEPT) || \
+    defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS) || \
+    defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) || \
+    defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE("C++03 support was deprecated in Boost.System 1.82 and will be removed in Boost.System 1.84. Please open an issue in https://github.com/boostorg/system if you want it retained.")
+
+#endif
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_REQUIRES_CXX11_HPP_INCLUDED

include/boost/system/result.hpp

@@ -85,6 +85,10 @@ template<class T> using remove_cvref = typename std::remove_cv< typename std::re
 
 template<class... T> using is_errc_t = std::is_same<mp11::mp_list<remove_cvref<T>...>, mp11::mp_list<errc::errc_t>>;
 
+template<class T, class... A> struct is_constructible: std::is_constructible<T, A...> {};
+template<class A> struct is_constructible<bool, A>: std::is_convertible<A, bool> {};
+template<class A> struct is_constructible<bool const, A>: std::is_convertible<A, bool> {};
+
 } // namespace detail
 
 // result
@@ -141,9 +145,9 @@ public:
 
     // explicit, value
     template<class... A, class En = typename std::enable_if<
-        std::is_constructible<T, A...>::value &&
+        detail::is_constructible<T, A...>::value &&
         !(detail::is_errc_t<A...>::value && std::is_arithmetic<T>::value) &&
-        !std::is_constructible<E, A...>::value &&
+        !detail::is_constructible<E, A...>::value &&
         sizeof...(A) >= 1
         >::type>
     explicit constexpr result( A&&... a )
@@ -154,8 +158,8 @@ public:
 
     // explicit, error
     template<class... A, class En2 = void, class En = typename std::enable_if<
-        !std::is_constructible<T, A...>::value &&
-        std::is_constructible<E, A...>::value &&
+        !detail::is_constructible<T, A...>::value &&
+        detail::is_constructible<E, A...>::value &&
         sizeof...(A) >= 1
         >::type>
     explicit constexpr result( A&&... a )
@@ -187,7 +191,8 @@ public:
     // converting
     template<class T2, class E2, class En = typename std::enable_if<
         std::is_convertible<T2, T>::value &&
-        std::is_convertible<E2, E>::value
+        std::is_convertible<E2, E>::value &&
+        !std::is_convertible<result<T2, E2> const&, T>::value
         >::type>
     BOOST_CXX14_CONSTEXPR result( result<T2, E2> const& r2 )
         noexcept(
@@ -205,7 +210,8 @@ public:
 
     template<class T2, class E2, class En = typename std::enable_if<
         std::is_convertible<T2, T>::value &&
-        std::is_convertible<E2, E>::value
+        std::is_convertible<E2, E>::value &&
+        !std::is_convertible<result<T2, E2>&&, T>::value
         >::type>
     BOOST_CXX14_CONSTEXPR result( result<T2, E2>&& r2 )
         noexcept(
@@ -395,12 +401,18 @@ public:
 
     // error access
 
-    constexpr E error() const
+    constexpr E error() const &
         noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_copy_constructible<E>::value )
     {
         return has_error()? variant2::unsafe_get<1>( v_ ): E();
     }
 
+    BOOST_CXX14_CONSTEXPR E error() &&
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_move_constructible<E>::value )
+    {
+        return has_error()? std::move( variant2::unsafe_get<1>( v_ ) ): E();
+    }
+
     // emplace
 
     template<class... A>
@@ -575,12 +587,18 @@ public:
 
     // error access
 
-    constexpr E error() const
+    constexpr E error() const &
         noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_copy_constructible<E>::value )
     {
         return has_error()? variant2::unsafe_get<1>( v_ ): E();
     }
 
+    BOOST_CXX14_CONSTEXPR E error() &&
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_move_constructible<E>::value )
+    {
+        return has_error()? std::move( variant2::unsafe_get<1>( v_ ) ): E();
+    }
+
     // emplace
 
     BOOST_CXX14_CONSTEXPR void emplace()

test/CMakeLists.txt

@@ -161,3 +161,6 @@ boost_test(TYPE run SOURCES result_value_construct3.cpp)
 boost_test(TYPE run SOURCES result_error_construct3.cpp)
 boost_test(TYPE run SOURCES result_emplace.cpp)
 boost_test(TYPE run SOURCES result_error_construct4.cpp)
+boost_test(TYPE run SOURCES result_value_construct4.cpp)
+boost_test(TYPE run SOURCES result_value_construct5.cpp)
+boost_test(TYPE run SOURCES result_error_move.cpp)

test/Jamfile.v2

@@ -191,3 +191,6 @@ run result_value_construct3.cpp : : : $(CPP11) ;
 run result_error_construct3.cpp : : : $(CPP11) ;
 run result_emplace.cpp : : : $(CPP11) ;
 run result_error_construct4.cpp : : : $(CPP11) ;
+run result_value_construct4.cpp : : : $(CPP11) ;
+run result_value_construct5.cpp : : : $(CPP11) ;
+run result_error_move.cpp : : : $(CPP11) ;

test/result_error_move.cpp

@@ -0,0 +1,91 @@
+// Copyright 2023 Klemens Morgenstern
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <string>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+
+    explicit X( int v = 0 ): v_( v ) {}
+
+    X( X const& ) = delete;
+    X& operator=( X const& ) = delete;
+
+    X( X && ) = default;
+    X& operator=( X && ) = default;
+};
+
+int main()
+{
+    {
+        result<std::string, X> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 1 );
+    }
+
+    {
+        BOOST_TEST(( !result<std::string, X>( 1 ).has_value() ));
+        BOOST_TEST(( result<std::string, X>( 1 ).has_error() ));
+
+        BOOST_TEST_EQ( (result<std::string, X>( 1 ).error().v_), 1 );
+    }
+
+    {
+        result<std::string, X> r( "s" );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        BOOST_TEST(( result<std::string, X>( "s" ).has_value() ));
+        BOOST_TEST(( !result<std::string, X>( "s" ).has_error() ));
+
+        BOOST_TEST_EQ( (result<std::string, X>( "s" ).error().v_), 0 );
+    }
+
+      {
+        result<void, X> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 1 );
+    }
+
+    {
+        BOOST_TEST(( !result<void, X>( 1 ).has_value() ));
+        BOOST_TEST(( result<void, X>( 1 ).has_error() ));
+
+        BOOST_TEST_EQ( (result<void, X>( 1 ).error().v_), 1 );
+    }
+
+    {
+        result<void, X> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        BOOST_TEST(( result<void, X>().has_value() ));
+        BOOST_TEST(( !result<void, X>().has_error() ));
+
+        BOOST_TEST_EQ( (result<void, X>().error().v_), 0 );
+    }
+
+    return boost::report_errors();
+}

test/result_value_construct4.cpp

@@ -0,0 +1,59 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+// Tricky mixed construction cases
+// https://github.com/boostorg/system/issues/104
+// https://brevzin.github.io//c++/2023/01/18/optional-construction/
+
+int main()
+{
+    {
+        result<int> r( make_error_code( errc::invalid_argument ) );
+        result<result<int>> r2( r );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> r( 5 );
+        result<result<int>> r2( r );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> const r( make_error_code( errc::invalid_argument ) );
+        result<result<int>> r2( r );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> const r( 5 );
+        result<result<int>> r2( r );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> r( make_error_code( errc::invalid_argument ) );
+        result<result<int>> r2( std::move( r ) );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> r( 5 );
+        result<result<int>> r2( std::move( r ) );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    return boost::report_errors();
+}

test/result_value_construct5.cpp

@@ -0,0 +1,86 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER) && _MSC_VER < 1910
+# pragma warning( disable: 4800 ) // forcing value to bool 'true' or 'false'
+#endif
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <utility>
+#include <type_traits>
+
+using namespace boost::system;
+
+// Tricky mixed construction cases
+// https://github.com/boostorg/system/issues/104
+// https://brevzin.github.io//c++/2023/01/18/optional-construction/
+
+template<class R1, class R2> void test()
+{
+    {
+        R1 r1( make_error_code( errc::invalid_argument ) );
+        R2 r2( r1 );
+
+        BOOST_TEST( !r2.has_value() );
+    }
+
+    {
+        R1 r1( 0 );
+        R2 r2( r1 );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), false );
+    }
+
+    {
+        R1 r1( 1 );
+        R2 r2( r1 );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), true );
+    }
+
+    {
+        R1 r1( make_error_code( errc::invalid_argument ) );
+        R2 r2( std::move( r1 ) );
+
+        BOOST_TEST( !r2.has_value() );
+    }
+
+    {
+        R1 r1( 0 );
+        R2 r2( std::move( r1 ) );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), false );
+    }
+
+    {
+        R1 r1( 1 );
+        R2 r2( std::move( r1 ) );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), true );
+    }
+}
+
+struct X
+{
+};
+
+int main()
+{
+    test< result<int>, result<bool> >();
+    test< result<int> const, result<bool> >();
+
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, result<X>&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, result<X> const&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, result<X>&&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, result<X> const&&>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const>, result<X>&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const>, result<X> const&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const>, result<X>&&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const>, result<X> const&&>));
+
+    return boost::report_errors();
+}