호출 연산자 오버로딩, 함수 객체

#include <iostream>
#include <algorithm>
#include <functional>
 
using namespace std;
 
class Max
{
public:
    int operator()(int x, int y)
    {
        return max(x, y);
    }
};
 
 
class AccMax
{
private:
    // 일반 함수와는 다르게 상태를 저장할 수 있다
    int _max = numeric_limits<int>::min();
 
public:
    int operator()(int x)
    {
        return _max = max(x, _max);
    }
};
 
 
struct Average
{
private:
    double _total = 0;
    int _times = 0;
 
public:
    double operator()(double value)
    {
        _times += 1;
        _total += value;
        return _total / _times;
    }
};
 
 
struct Print
{
public:
    void operator()(int v) const
    {
        cout << v << endl;
    }
};
 
int main()
{
    Max mx;
    cout << mx(1, 2) << endl;
    cout << mx(2, 3) << endl;
    cout << mx(3, 4) << endl;
    cout << mx(5, 6) << endl;
 
 
    AccMax amx;
    cout << amx(1) << endl;
    cout << amx(3) << endl;
    cout << amx(5) << endl;
    cout << amx(2) << endl;
    cout << amx(4) << endl;
    cout << amx(6) << endl;
 
 
    Average avg;
    cout << avg(100) << endl;
    cout << avg(200) << endl;
    cout << avg(300) << endl;
 
 
    Print print;
    int nums[] = { 1, 2, 3, 4, 5 };
    std::for_each(nums, nums + size(nums), print);
 
    function<void(int)> func = print;
    func(1);
 
    plus<int> p; // 함수 객체
    cout << p(1, 2) << endl;
 
    negate<int> n; // 함수 객체
    cout << n(1) << endl;
 
    equal_to<int> et; // 함수 객체
    cout << et(1, 1) << endl;
}