[Boost-users] enable_if and multiple partial specializations

Subject: [Boost-users] enable_if and multiple partial specializations
From: Gennadiy Rozental (rogeeff_at_[hidden])
Date: 2011-04-08 04:59:02

Hi,

It's late and I might be missing something, but I can't figure out how can I use
enable_if to disambiguate 2 partial specializations where one is subcase of
another one:

#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_enum.hpp>
#include <boost/type_traits/is_scalar.hpp>

#include <iostream>

template<typename T, typename Enabler=void>
struct M {
    static void foo() { std::cout << "generic" << std::endl; }
};

template<typename T>
struct M<T, typename boost::enable_if<boost::is_scalar<T> >::type> {
    static void foo() { std::cout << "scalar" << std::endl; }
};

template<typename T>
struct M<T,typename boost::enable_if<boost::is_enum<T> >::type> {
    static void foo() { std::cout << "enum" << std::endl; }
};

struct S {};
enum FOO { FOO1, FOO2 };

int main()
{
    M<S>::foo();
    M<int>::foo();
    M<FOO>::foo();
}

---------------

M<FOO>::foo() fails to compile due to ambiguity. 

Any pointers? Or How to get what I want?

Gennadiy