Disable use of <shared_mutex> under the XP toolsets (v140_xp and v141_xp). Fixes #110.

Closes #108.

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/mutex.hpp

@@ -31,7 +31,9 @@ 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
@@ -40,6 +42,14 @@ struct mutex
 
 #include <shared_mutex>
 
+#if BOOST_MSSTL_VERSION >= 142 || _HAS_SHARED_MUTEX
+# define BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX
+#endif
+
+#endif
+
+#if defined(BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX)
+
 namespace boost
 {
 namespace system
@@ -53,7 +63,7 @@ typedef std::shared_mutex mutex;
 } // namespace system
 } // namespace boost
 
-#else
+#else // defined(BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX)
 
 #include <mutex>
 
@@ -70,7 +80,8 @@ 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/result.hpp

@@ -401,12 +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>
@@ -581,12 +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

@@ -163,3 +163,4 @@ 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

@@ -193,3 +193,4 @@ 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();
+}