// function::target example
#include <iostream>     // std::cout, std::boolalpha
#include <functional>   // std::function, std::plus, std::minus

int my_plus (int a, int b) {return a+b;}
int my_minus (int a, int b) {return a-b;}

int main () {
  std::function<int(int,int)> foo = my_plus;
  std::function<int(int,int)> bar = std::plus<int>();

  // calling using functional form:
  std::cout << foo(100,20) << '\n';
  std::cout << bar(100,20) << '\n';

  // calling by invoking target:
  std::cout << (*foo.target<int(*)(int,int)>())(100,20) << '\n';
  std::cout << (*bar.target<std::plus<int>>())(100,20) << '\n';

  // changing target directly:
  *foo.target<int(*)(int,int)>() = &my_minus;
  std::cout << foo(100,20) << '\n';

  return 0;
}