Here's another use case that fails to compile in C++03 but compiles successfully in C++11. (Note, it fails to compile in VS2005 and g++ 4.8.2 -std=c++98, and compiles successfully with g++ 4.8.2 -std=c++11) MOC is a BOOST_MOVABLE_BUT_NOT_COPYABLE type. Foo is an empty with an implicit conversion function to MOC. "MOC m(Foo());" compiles successfully but "MOC m2(makeFoo());" fails to compile. Is this a bug or a limitation of Boost.Move in C++03? //---------- //Start Code //---------- #include <boost/move/core.hpp> #include <boost/move/utility.hpp> struct MOC { MOC() : value(121) {} MOC(BOOST_RV_REF(MOC) rhs) : value(rhs.value) {} int value; private: BOOST_MOVABLE_BUT_NOT_COPYABLE(MOC) }; struct Foo { operator MOC () { return MOC(); } }; Foo makeFoo() { return Foo(); } int main() { // (1) Successfully Compiles. MOC m(Foo()); // (2) Fails to Compile. MOC m2(makeFoo()); return 0; } //-------- //End Code //-------- //-------------------- //Start Error Messages //-------------------- boost_move_implicit_conversion_to_rvalue.cc: In function ‘int main()’: boost_move_implicit_conversion_to_rvalue.cc:32:19: error: no matching function for call to ‘MOC::MOC(Foo)’ MOC m2(makeFoo()); ^ boost_move_implicit_conversion_to_rvalue.cc:32:19: note: candidates are: boost_move_implicit_conversion_to_rvalue.cc:10:3: note: MOC::MOC(MOC&) BOOST_MOVABLE_BUT_NOT_COPYABLE(MOC) ^ boost_move_implicit_conversion_to_rvalue.cc:10:3: note: no known conversion for argument 1 from ‘Foo’ to ‘MOC&’ boost_move_implicit_conversion_to_rvalue.cc:7:3: note: MOC::MOC(boost::rv<MOC>&) MOC(BOOST_RV_REF(MOC) rhs) : value(rhs.value) {} ^ boost_move_implicit_conversion_to_rvalue.cc:7:3: note: no known conversion for argument 1 from ‘Foo’ to ‘boost::rv<MOC>&’ boost_move_implicit_conversion_to_rvalue.cc:6:3: note: MOC::MOC() MOC() : value(121) {} ^ boost_move_implicit_conversion_to_rvalue.cc:6:3: note: candidate expects 0 arguments, 1 provided //------------------ //End Error Messages //------------------