Re: [boost] [move] problem with msvc and BOOST_MOVABLE_BUT_NOT_COPYABLE

Subject: Re: [boost] [move] problem with msvc and BOOST_MOVABLE_BUT_NOT_COPYABLE
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2010-05-28 14:13:48

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_at_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