#include <iostream>

using namespace std;

    template<typename T>
    struct is_pure_func_ptr: public std::false_type {};
    template<typename Ret, typename... Args>
    struct is_pure_func_ptr<Ret(Args...)>: public std::true_type {};//detecting functions themselves
    template<typename Ret, typename... Args>
    struct is_pure_func_ptr<Ret(*)(Args...)>: public std::true_type {};//detecting function pointers
void f1()
{};

int f2(int)
{};

int f3(int, int)
{};

struct Functor
{
    void operator ()()
    {}
};

int main()
{
    cout << is_pure_func_ptr<decltype(f1)>::value << endl; // output true
    cout << is_pure_func_ptr<decltype(f2)>::value << endl; // output true
    cout << is_pure_func_ptr<decltype(f3)>::value << endl; // output true
    cout << is_pure_func_ptr<decltype(&f3)>::value << endl; // output true
    cout << is_pure_func_ptr<Functor>::value << endl;      // output false
    cout << is_pure_func_ptr<char*>::value << endl;        // output false
}