gistfile1.cpp

#include <functional>
#include <iostream>

// Detect whether the function takes an int argument or zero arguments
template<typename T, typename = decltype(std::declval<T>()(0))> std::true_type detect_type(const T&);
template<typename T, typename = decltype(std::declval<T>()())> std::false_type detect_type(const T&);

int main()
{
	auto a = std::bind([](int){}, std::placeholders::_1); // Prints 1
	//auto a = std::bind([](){}, std::placeholders::_1); // Prints 0
	std::cout << decltype(detect_type(a))::value << std::endl;
}