Documented limitations reported in Trac #12194 and Trac #12307

doc/move.qbk

@@ -661,6 +661,32 @@ An alternative is to implement a single `operator =()` for copyable and movable
 However, "pass by value" is not optimal for classes (like containers, strings, etc.) that reuse resources
 (like previously allocated memory) when x is assigned from a lvalue.
 
+[endsect]
+
+[section:templated_assignment_operator Templated assignment operator in copyable and movable types]
+
+
+[import ../example/doc_template_assign.cpp]
+
+Given a movable and copyable class, if a templated assignment operator (*) is added:
+
+[template_assign_example_foo_bar]
+
+C++98 and C++11 compilers will behave different when assigning from a `[const] Foo` lvalue:
+
+[template_assign_example_main]
+
+This different behaviour is a side-effect of the move emulation that can't be easily avoided by
+[*Boost.Move]. One workaround is to SFINAE-out the templated assignment operator with `disable_if`:
+
+[c++]
+
+   template<class U> // Modified templated assignment
+   typename boost::disable_if<boost::is_same<U, Foo>, Foo&>::type
+      operator=(const U& rhs)
+   {  i = -rhs.i; return *this;  } //(2)
+
+
 [endsect]
 
 [endsect]
@@ -762,6 +788,14 @@ Many thanks to all boosters that have tested, reviewed and improved the library.
 
 [section:release_notes Release Notes]
 
+[section:release_notes_boost_1_62 Boost 1.62 Release]
+
+*  Documented new limitations reported in Trac tickets
+   [@https://svn.boost.org/trac/boost/ticket/12194 #12194 ['"Copy assignment on moveable and copyable classes uses wrong type"]] and
+   [@https://svn.boost.org/trac/boost/ticket/12307 #12307 ['"Copy assignment on moveable and copyable classes uses wrong type"]].
+
+[endsect]
+
 [section:release_notes_boost_1_61 Boost 1.61 Release]
 
 *  Experimental: asymptotically optimal bufferless merge and sort algorithms: [funcref boost::movelib::adaptive_merge adaptive_merge]

example/doc_template_assign.cpp

@@ -0,0 +1,98 @@
+//////////////////////////////////////////////////////////////////////////////
+//
+// (C) Copyright Ion Gaztanaga 2014-2014.
+// 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)
+//
+// See http://www.boost.org/libs/move for documentation.
+//
+//////////////////////////////////////////////////////////////////////////////
+
+#include <boost/move/detail/config_begin.hpp>
+#include <boost/move/detail/meta_utils_core.hpp>
+
+#include <boost/move/move.hpp>
+
+//[template_assign_example_foo_bar
+
+class Foo
+{
+   BOOST_COPYABLE_AND_MOVABLE(Foo)
+
+   public:
+   int i;
+   explicit Foo(int val)      : i(val)   {}
+
+   Foo(BOOST_RV_REF(Foo) obj) : i(obj.i) {}
+
+   Foo& operator=(BOOST_RV_REF(Foo) rhs)
+   {  i = rhs.i; rhs.i = 0; return *this; }
+
+   Foo& operator=(BOOST_COPY_ASSIGN_REF(Foo) rhs)
+   {  i = rhs.i; return *this;   } //(1)
+
+   template<class U> //(*) TEMPLATED ASSIGNMENT, potential problem
+   //<-
+   #if 1
+   typename ::boost::move_detail::disable_if_same<U, Foo, Foo&>::type
+   operator=(const U& rhs)
+   #else
+   //->
+   Foo& operator=(const U& rhs)
+   //<-
+   #endif
+   //->
+   {  i = -rhs.i; return *this;  } //(2)
+};
+//]
+
+struct Bar
+{
+   int i;
+   explicit Bar(int val) : i(val) {}
+};
+
+
+//<-
+#ifdef NDEBUG
+#undef NDEBUG
+#endif
+//->
+#include <cassert>
+
+int main()
+{
+//[template_assign_example_main
+   Foo foo1(1);
+   //<-
+   assert(foo1.i == 1);
+   //->
+   Foo foo2(2);
+   //<-
+   assert(foo2.i == 2);
+   Bar bar(3);
+   assert(bar.i == 3);
+   //->
+   foo2 = foo1; // Calls (1) in C++11 but (2) in C++98
+   //<-
+   assert(foo2.i == 1);
+   assert(foo1.i == 1); //Fails in C++98 unless workaround is applied
+   foo1 = bar;
+   assert(foo1.i == -3);
+   foo2 = boost::move(foo1);
+   assert(foo1.i == 0);
+   assert(foo2.i == -3);
+   //->
+   const Foo foo5(5);
+   foo2 = foo5; // Calls (1) in C++11 but (2) in C++98
+   //<-
+   assert(foo2.i == 5); //Fails in C++98 unless workaround is applied
+   assert(foo5.i == 5);
+   //->
+//]
+   return 0;
+}
+
+
+#include <boost/move/detail/config_end.hpp>

include/boost/move/detail/meta_utils_core.hpp

@@ -114,6 +114,18 @@ struct is_same<T, T>
    static const bool value = true;
 };
 
+//////////////////////////////////////
+//        enable_if_same
+//////////////////////////////////////
+template <class T, class U, class R = void>
+struct enable_if_same : enable_if<is_same<T, U>, R> {};
+
+//////////////////////////////////////
+//        disable_if_same
+//////////////////////////////////////
+template <class T, class U, class R = void>
+struct disable_if_same : disable_if<is_same<T, U>, R> {};
+
 }  //namespace move_detail {
 }  //namespace boost {
 

proj/vc7ide/Move.sln

@@ -127,6 +127,10 @@ Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "adaptive_merge_test", "adap
 	ProjectSection(ProjectDependencies) = postProject
 	EndProjectSection
 EndProject
+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "doc_template_assign", "doc_template_assign.vcproj", "{7460CA18-D532-E4F8-F1F2-3A796D2A91E2}"
+	ProjectSection(ProjectDependencies) = postProject
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfiguration) = preSolution
 		Debug = Debug
@@ -263,6 +267,10 @@ Global
 		{CD617A28-6217-B79E-4CE2-6BA035379A6A}.Debug.Build.0 = Debug|Win32
 		{CD617A28-6217-B79E-4CE2-6BA035379A6A}.Release.ActiveCfg = Release|Win32
 		{CD617A28-6217-B79E-4CE2-6BA035379A6A}.Release.Build.0 = Release|Win32
+		{7460CA18-D532-E4F8-F1F2-3A796D2A91E2}.Debug.ActiveCfg = Debug|Win32
+		{7460CA18-D532-E4F8-F1F2-3A796D2A91E2}.Debug.Build.0 = Debug|Win32
+		{7460CA18-D532-E4F8-F1F2-3A796D2A91E2}.Release.ActiveCfg = Release|Win32
+		{7460CA18-D532-E4F8-F1F2-3A796D2A91E2}.Release.Build.0 = Release|Win32
 	EndGlobalSection
 	GlobalSection(SolutionItems) = postSolution
 		..\..\..\..\boost\move\algo\adaptive_merge.hpp = ..\..\..\..\boost\move\algo\adaptive_merge.hpp

proj/vc7ide/doc_template_assign.vcproj

@@ -0,0 +1,134 @@
+<?xml version="1.0" encoding="Windows-1252"?>
+<VisualStudioProject
+	ProjectType="Visual C++"
+	Version="7.10"
+	Name="doc_template_assign"
+	ProjectGUID="{7460CA18-D532-E4F8-F1F2-3A796D2A91E2}"
+	Keyword="Win32Proj">
+	<Platforms>
+		<Platform
+			Name="Win32"/>
+	</Platforms>
+	<Configurations>
+		<Configuration
+			Name="Debug|Win32"
+			OutputDirectory="../../Bin/Win32/Debug"
+			IntermediateDirectory="Debug/doc_template_assign"
+			ConfigurationType="1"
+			CharacterSet="2">
+			<Tool
+				Name="VCCLCompilerTool"
+				Optimization="0"
+				AdditionalIncludeDirectories="../../../.."
+				PreprocessorDefinitions="WIN32;_DEBUG;_CONSOLE;BOOST_DATE_TIME_NO_LIB"
+				MinimalRebuild="TRUE"
+				BasicRuntimeChecks="3"
+				RuntimeLibrary="3"
+				DisableLanguageExtensions="FALSE"
+				TreatWChar_tAsBuiltInType="TRUE"
+				ForceConformanceInForLoopScope="TRUE"
+				UsePrecompiledHeader="0"
+				WarningLevel="4"
+				Detect64BitPortabilityProblems="TRUE"
+				DebugInformationFormat="3"/>
+			<Tool
+				Name="VCCustomBuildTool"/>
+			<Tool
+				Name="VCLinkerTool"
+				AdditionalDependencies="winmm.lib"
+				OutputFile="$(OutDir)/doc_template_assign_d.exe"
+				LinkIncremental="1"
+				AdditionalLibraryDirectories="../../../../stage/lib"
+				GenerateDebugInformation="TRUE"
+				ProgramDatabaseFile="$(OutDir)/doc_template_assign.pdb"
+				SubSystem="1"
+				TargetMachine="1"
+				FixedBaseAddress="1"/>
+			<Tool
+				Name="VCMIDLTool"/>
+			<Tool
+				Name="VCPostBuildEventTool"/>
+			<Tool
+				Name="VCPreBuildEventTool"/>
+			<Tool
+				Name="VCPreLinkEventTool"/>
+			<Tool
+				Name="VCResourceCompilerTool"/>
+			<Tool
+				Name="VCWebServiceProxyGeneratorTool"/>
+			<Tool
+				Name="VCXMLDataGeneratorTool"/>
+			<Tool
+				Name="VCWebDeploymentTool"/>
+			<Tool
+				Name="VCManagedWrapperGeneratorTool"/>
+			<Tool
+				Name="VCAuxiliaryManagedWrapperGeneratorTool"/>
+		</Configuration>
+		<Configuration
+			Name="Release|Win32"
+			OutputDirectory="../../Bin/Win32/Release"
+			IntermediateDirectory="Release/doc_template_assign"
+			ConfigurationType="1"
+			CharacterSet="2">
+			<Tool
+				Name="VCCLCompilerTool"
+				AdditionalIncludeDirectories="../../../.."
+				PreprocessorDefinitions="WIN32;NDEBUG;_CONSOLE;BOOST_DATE_TIME_NO_LIB"
+				RuntimeLibrary="2"
+				TreatWChar_tAsBuiltInType="TRUE"
+				ForceConformanceInForLoopScope="FALSE"
+				UsePrecompiledHeader="0"
+				WarningLevel="4"
+				Detect64BitPortabilityProblems="TRUE"
+				DebugInformationFormat="0"/>
+			<Tool
+				Name="VCCustomBuildTool"/>
+			<Tool
+				Name="VCLinkerTool"
+				AdditionalDependencies="winmm.lib"
+				OutputFile="$(OutDir)/doc_template_assign.exe"
+				LinkIncremental="1"
+				AdditionalLibraryDirectories="../../../../stage/lib"
+				GenerateDebugInformation="TRUE"
+				SubSystem="1"
+				OptimizeReferences="2"
+				EnableCOMDATFolding="2"
+				TargetMachine="1"/>
+			<Tool
+				Name="VCMIDLTool"/>
+			<Tool
+				Name="VCPostBuildEventTool"/>
+			<Tool
+				Name="VCPreBuildEventTool"/>
+			<Tool
+				Name="VCPreLinkEventTool"/>
+			<Tool
+				Name="VCResourceCompilerTool"/>
+			<Tool
+				Name="VCWebServiceProxyGeneratorTool"/>
+			<Tool
+				Name="VCXMLDataGeneratorTool"/>
+			<Tool
+				Name="VCWebDeploymentTool"/>
+			<Tool
+				Name="VCManagedWrapperGeneratorTool"/>
+			<Tool
+				Name="VCAuxiliaryManagedWrapperGeneratorTool"/>
+		</Configuration>
+	</Configurations>
+	<References>
+	</References>
+	<Files>
+		<Filter
+			Name="Source Files"
+			Filter="cpp;c;cxx;def;odl;idl;hpj;bat;asm;asmx"
+			UniqueIdentifier="{475F3C87-6465-7BC5-05A6-2454C0A2A2CF}">
+			<File
+				RelativePath="..\..\example\doc_template_assign.cpp">
+			</File>
+		</Filter>
+	</Files>
+	<Globals>
+	</Globals>
+</VisualStudioProject>