SFINAE working in return type but not as template parameter

Question

I already used the SFINAE idiom quite a few times and I got used to put my std::enable_if<> in template parameters rather than in return types. However, I

Answer 1

Values in the templates work:

template::value, int>::type = 0>
auto foo(T)
    -> void
{
    std::cout << "I'm an integer!\n";
}

template::value, int>::type = 0>
auto foo(T)
    -> void
{
    std::cout << "I'm a floating point number!\n";
}