[boost] [config] BOOST_NO_CXX11_HDR_FUNCTIONAL and VC++10

Subject: [boost] [config] BOOST_NO_CXX11_HDR_FUNCTIONAL and VC++10
From: Edward Diener (eldiener_at_[hidden])
Date: 2014-08-30 21:16:56

While BOOST_NO_CXX11_HDR_FUNCTIONAL is not defined for VC++10 my tests 
show that std::ref in VC++10 is broken in a very simple case. Here is 
the code for that case:

// test_vc10_refwrapper.cpp

#include <functional>

class p_functor_class_char
   {
   public:
   p_functor_class_char() : data('A') {}
   char operator()() { return data; }
   private:
   char data;
   };

void main()
   {
   p_functor_class_char pfcc;
   std::function<char ()> sf(std::ref(pfcc));
   }

which for VC++10 gives:

> c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\xxcallobj(13) : error C2440: 'return' : cannot convert from 'void' to 'char'
>         Expressions of type void cannot be converted to other types
>         c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\xxfunction(65) : see reference to function template instantiation '_Ret std::tr1::_Callable_obj<_Ty>::_ApplyX<_Rx>(void)' being compiled
>         with
>         [
>             _Ret=char,
>             _Ty=std::tr1::reference_wrapper<p_functor_class_char>,
>             _Rx=char
>         ]
>         c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\xxfunction(64) : while compiling class template member function 'char std::tr1::_Impl_no_alloc0<_Callable,_Rx>::_Do_call(void)'
>         with
>         [
>             _Callable=_MyWrapper,
>             _Rx=char
>         ]
>         c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\xxfunction(386) : see reference to class template instantiation 'std::tr1::_Impl_no_alloc0<_Callable,_Rx>' being compiled
>         with
>         [
>             _Callable=_MyWrapper,
>             _Rx=char
>         ]
>         c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\xxfunction(369) : see reference to function template instantiation 'void std::tr1::_Function_impl0<_Ret>::_Reset0o<_Myimpl,_Fty,std::allocator<_Ty>>(_Fty,_Alloc)' being compiled
>         with
>         [
>             _Ret=char,
>             _Fty=std::tr1::reference_wrapper<p_functor_class_char>,
>             _Ty=std::tr1::_Function_impl0<char>,
>             _Alloc=std::allocator<std::tr1::_Function_impl0<char>>
>         ]
>         c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\functional(126) : see reference to function template instantiation 'void std::tr1::_Function_impl0<_Ret>::_Reset<std::tr1::reference_wrapper<_Ty>>(_Fty)' being compiled
>         with
>         [
>             _Ret=char,
>             _Ty=p_functor_class_char,
>             _Fty=std::tr1::reference_wrapper<p_functor_class_char>
>         ]
>         test_vc10_refwrapper.cpp(15) : see reference to function template instantiation 'std::tr1::function<_Fty>::function<p_functor_class_char>(std::tr1::reference_wrapper<_Ty>)' being compiled
>         with
>         [
>             _Fty=char (void),
>             _Ty=p_functor_class_char
>         ]

With VC++11 and VC++12 this has been fixed. Using boost::function and 
boost::ref there are no problems in VC++10.

I realize that this might not really be an issue in Boost but I was 
still wondering if this is a known problem with any Boost developers. I 
ran into it during tests, where I was letting 
BOOST_NO_CXX11_HDR_FUNCTIONAL determine whether to use std or boost 
versions of the functionality in the C++11 <functional> header.