// http://en.cppreference.com/w/cpp/utility/functional/invoke
#include <functional>
#include <iostream>
 
struct Foo {
    Foo(int num) : num_(num) {}
    void print_add(int i) const { std::cout << num_+i << '\n'; }
    int num_;
};
 
void print_num(int i){ std::cout << i << '\n'; }
 
struct PrintNum {
    void operator()(int i) const { std::cout << i << '\n';}
};
 
int main()
{
    // invoke a free function
    std::invoke(print_num, -9);
    // store a free function
    std::function<void(int)> f_display = print_num;
    f_display(-9);
    
    // invoke a lambda
    std::invoke([]() { print_num(42); });
    // store a lambda
    std::function<void()> f_display_42 = []() { print_num(42); };
    f_display_42();
 
    // invoke a member function
    const Foo foo(314159);
    std::invoke(&Foo::print_add, foo, 1);
    // store a call to a member function
    std::function<void(const Foo&, int)> f_add_display = &Foo::print_add;
    f_add_display(foo, 1);
    f_add_display(314159, 1);
    // store a call to a member function and object
    using std::placeholders::_1;
    std::function<void(int)> f_add_display2 = std::bind( &Foo::print_add, foo, _1 );
    f_add_display2(2);
    // store a call to a member function and object ptr
    std::function<void(int)> f_add_display3 = std::bind( &Foo::print_add, &foo, _1 );
    f_add_display3(3);
  
    // invoke (access) a data member
    std::cout << "num_: " << std::invoke(&Foo::num_, foo) << '\n';
    // store a call to a data member accessor
    std::function<int(Foo const&)> f_num = &Foo::num_;
    std::cout << "num_: " << f_num(foo) << '\n';
 
    // invoke a function object
    std::invoke(PrintNum(), 18);
    // store a call to a function object
    std::function<void(int)> f_display_obj = PrintNum();
    f_display_obj(18);

    // store the result of a call to std::bind
    std::function<void()> f_display_31337 = std::bind(print_num, 31337);
    f_display_31337();

}