Member function template argument default value

Question

The following bit of code compiles in GCC 4.5.3 but does not compile in VS 2008 and 2010. Is this due to a VS compiler bug or does the standard forbid giving default function template argument values?

#include <cstdlib>

struct Bar
{
    enum Group{ A , B , C };
};

struct Foo
{
    template<typename T>
    static void getSome( typename T::Group = T::A );
};

template<typename T>
void Foo::getSome( typename T::Group )
{
};

int main()
{
    Foo::getSome<Bar>();            // Does not compile in VS 2008 & 2010 (compiles in gcc 4.5.3)
    Foo::getSome<Bar>( Bar::C );    // Compiles in VS 2008 and gcc 4.5.3
    return EXIT_SUCCESS;
}

Error message

prog.cpp(11) : error C2589: '::' : illegal token on right side of '::'
prog.cpp(11) : error C2059: syntax error : '::'

Answer 1

It is a MSVC bug.

The bug is in the handling of template functions with default parameters, as you probably guessed.

Their workaround is to supply all function parameters. (yuck)

Acknowledged here.

Answer 2

I think g++ is adhering to the standard when it compiles your snippet.

The following extract should be the reference to the right part of the standard (section 14.1.9):

A default template-argument is a template-argument (14.3) specified after = in a template-parameter. A default template-argument may be specified for any kind of template-parameter (type, non-type, template) that is not a template parameter pack (14.5.3). A default template-argument may be specified in a template declaration. A default template-argument shall not be specified in the template-parameter-lists of the definition of a member of a class template that appears outside of the member’s class. A default template-argument shall not be specified in a friend class template declaration. If a friend function template declaration specifies a default template-argument, that declaration shall be a definition and shall be the only declaration of the function template in the translation unit.