On 28/05/2010 19:32, Thomas Klimpel wrote:
The expectation that the statement "return x;" will benefit from RVO might not be justified here. Writing "return boost::move(x);" might actually be a good idea.
GCC 4.4.1 with -std=gnu++0x behaves similarly to boost.move emulation: volatile int cond = 0; class X { X(const X&); X& operator=(const X&); public: X(){} X(X&&){} X& operator=(X&&){} static X create() { X x, x2; return cond ? x : x2; // passing value form static member-fn } }; int main() { X x(X::create()); return 0; } $ gcc test.cpp -std=gnu++0x C:\Users\IGAZTA~1\AppData\Local\Temp\ccUoS3Ag.o:test.cpp:(.text$_ZN1X6createEv[X::create()]+0x46): undefined reference to `X::X(X const&)' collect2: ld returned 1 exit status Same with MSVC-10.0: 1>------ Build started: Project: test, Configuration: Debug Win32 ------ 1> test.cpp 1>test.obj : error LNK2001: unresolved external symbol "private: __thiscall X::X(class X const &)" (??0X@@AAE@ABV0@@Z) 1>c:\users\igaztanaga\documents\visual studio 2010\Projects\test\Debug\test.exe : fatal error LNK1120: 1 unresolved externals But I would expect a compile-time error. All fine if we change the return statement to: return cond ? static_cast<X&&>(x) : static_cast<X&&>(x2); Best, Ion