function型の変数

#include <functional>
#include <iostream>

using namespace std;

int f(int x, int y){
  return x + y;
}

int main(){
  function<int(int, int)> f2;
  f2 = f;
  cout << f2(1, 2) << endl;
  f2 = [](int a, int b){ return a * b; };
  cout << f2(2, 3) << endl;
}