#include <iostream>

struct Functor
{
        int operator()(int a, int b)
        {
                std::cout << "Calling functor with " << a << " and " << b << std::endl;
                return a + b;
        }
};

template<class T>
T make_instance();

template<class T>
struct LogAnyFunctor : public T
{
        template<typename... Args>
        auto operator()(Args... args) -> decltype(make_instance<T>()(args...))
        {
                std::cout << "Before" << std::endl;
                int res = T::operator()(args...);
                std::cout << "After" << std::endl;
                return res;
        }
};


int main()
{
        LogAnyFunctor<Functor> a;
        std::cout << a(2, 3) << std::endl;
}