`std::enable_if` is function pointer - how?

Question

I want to use SFINAE to enable a particular template if the user passes a function pointer as a parameter.

I have googled around but found nothing - I also

Answer 1

No SFINAE is needed to accept a function pointer or a member function pointer. To distinguish function objects from non-callable stuff SFINAE is needed, there's probably no way around this.

#include 
#include 

template 
void moo (Ret (*fp)(Parm...))
{
    std::cout << "funptr" << std::endl;
}

template 
void moo (Ret (Owner::*fp1)(Parm...))
{
    std::cout << "memfunptr" << std::endl;
}

template ())
                            (std::forward(std::declval())...))>
void moo (Funobj functor)
{
    std::cout << "funobj" << std::endl;
}

void x1() {}
struct X2 { void x2() {} };
struct X3 { void operator()(){} };


int main()
{
    moo(x1);
    moo(&X2::x2);
    moo(X3());
}