std::invoke

std::invoke was included in c++17 and are inside <functional>.

#include <iostream>
#include <functional>

int do_something(const int i)
{
    return 5+i;
}

struct S
{
    int j=5;
    int do_something(const int i)
    {
        return j+i;
    }

    int do_something_2(const int i)
    {
        return j*i;
    }
};

int main()
{
    //outputs 10
    std::cout << std::invoke(&do_something, 5) << '\n'; 
    
    //outputs 8
    S s;
    std::cout << s.do_something(3) << '\n';

    auto fp = &S::do_something; 
    int (S::*fp2)(int) = nullptr;

    if(true)
    {
        fp2 = &S::do_something_2;
    } else {
        fp2 = &S::do_seomthing
    }
    
    //outputs 7
    std::cout << (s.*fp)(2) <<'\n';
    std::cout << (s.*fp2)(1) <<'\n';



    std::cout << std::invoke(&S::do_something,   s, 10) << '\n';
    std::cout << std::invoke(&S::do_something_2, s, 10) << '\n';

    //we can even use std::invoke to access member data
    std::cout << std::invoke(&S::j, s) << '\n';
}

std::invoke gives universal interface for calling anything that’s callable. If we do any sort of passing around function pointer, or passing around member pointers, or any kind of templated programming that can take callable things, std::invoke could potentially save lots of efforts in the number of overloads that we need to implement.