Re: passing functor or function to template class

After the inspiring discussion, and particularly encouraged by Zoltan's SFINAE example, I finally found the solution myself. I'm sharing it here for the record and in case someone else might be interested.

#include <iostream>
template<typename T> struct isFunctionPointer {
    template<typename U> static char is_ptr(U (*)());
    static double is_ptr(...);
    static T t;
    enum {value = sizeof(is_ptr(t)) == sizeof(char)};
};
template<typename T, bool = isFunctionPointer<T>::value> struct Type {typedef T & U;};
template<typename T> struct Type<T, true> {typedef T U;};
// A function.
void *function() {
    std::cout << "function" << std::endl;
    return 0;
}
// A functor.
class Functor {
  public:
    Functor() {}
    void *operator()() {
        std::cout << "functor" << std::endl;
        return 0;
    }
  private:
    Functor(const Functor &);
} functor;
template<typename T> struct Reference {
    Reference(typename Type<T>::U t):f(t) {}
    typename Type<T>::U f;
};
// Test if it works.
int main() {
    Reference<void *(*)()> rf(function);
    Reference<Functor> rF(functor);
    rf.f();
    rF.f();
    return 0;
}