仿函数简单来说,就是重定义了成员函数operator()的一种自定义类型对象

	#include <iostream>
	using namespace std;
	
	class _functor
	{
	public:
		int operator()(int x, int y) { return x+y; }
	};
	
	int main()
	{
		_functor functor;
		cout << functor(1,3) << endl;
		
		return 0;
	}