#include <functional>
#include <iostream>
 
struct Foo {
    Foo(int num) : num_(num) {}
    void print_add(int i) const { std::cout << num_+i << '\n'; }
    int num_;
};
 
int main()
{
    std::function<void(const Foo&, int)> f_add_display = &Foo::print_add;
   const Foo foo(5);
    f_add_display(foo, 1);
}