[boost] enable_if quirk? bug?

Subject: [boost] enable_if quirk? bug?
From: Gennadiy Rozental (rogeeff_at_[hidden])
Date: 2012-11-11 02:20:46

Hi,

While working on some portability for Boost.Test I found this weird behavior. 
Abstracting out Boost.Test specific staff it goes like this:

template<typename T>
inline typename boost::enable_if_c<!boost::is_float<T>::value, int>::type
foo( T&& v );

template<typename T>
inline typename boost::enable_if_c<!boost::is_float<T>::value, int>::type
foo( T&& v )
{
    return 1;
}

...
foo(1);

MSVC 10 producing this error:

error C2668: 'foo' : ambiguous call to overloaded function
        test.cpp(31): could be 'int foo<int>(T &&)'
        with
        [
            T=int
        ]
        test.cpp(27): or       'int foo<int>(T &&)'
        with
        [
            T=int
        ]
        while trying to match the argument list '(int)'

Now change boost::enable_if_c with seemingly equivalent std::enable_if:

template<typename T>
inline typename std::enable_if<!boost::is_float<T>::value, int>::type
foo( T&& v );

template<typename T>
inline typename std::enable_if<!boost::is_float<T>::value, int>::type
foo( T&& v )
{
    return 1;
}

and MSVC 10 is happy to accept this code.

This is somewhat unfortunate since I hoped to use boost::enable_if across 
compilers.

Gennadiy