#include <iostream>

struct P{};

struct S{bool operator()(){return true;}};

template <class TFunctor>
class TIsCallable
{   
    typedef char TTwoChars[2];
    template <class T>
    static char Test(int[sizeof((*((T*)0))())]);

    template <class>
    static TTwoChars& Test(...);
public:
    static const bool Value_ = sizeof(Test<TFunctor>(0)) == 1;
};

int main()
{   
    std::cout
        << TIsCallable<int>::Value_
        << TIsCallable<P>::Value_
        << TIsCallable<int (*)()>::Value_
        << TIsCallable<S>::Value_ << std::endl;
}