Get function pointer from std::function when using std::bind

Question

I'm trying to use std::function in conjunction with std::bind, but I'm having some problems.

This works:

#include <functional>
#include <iostream>

void print() {
    std::cout << 2;
}

int main() {
    std::function<void ()> foo = print;
    (*foo.target<void (*)()>())(); //prints 3
}

This crashes at the second line of main:

#include <functional>
#include <iostream>

void print (int i) {
    std::cout << i;
}

int main() {
    std::function<void ()> foo = std::bind (print, 2);
    (*foo.target<void (*)()>())();
}

I'm really holding the std::function<void ()> and need to be able to return the function; not just call it. I expect the usage would be something like this:

#include <functional>
#include <iostream>

void print (int i) {
    std::cout << i;
}

int main() {
    Container c (std::bind (print, 2));

    //I would expect the original
    c.func() (3); //prints 3

    if (c.func() == print) /* this is what I'm mostly getting at */
}

Is there any way to get the original function to return it, or an alternative? It does kind of conflict with the return type as well, as void (*)() matches the bound signature quite nicely.

Answer 1

This is quite impossible. The whole reason that std::function exists is that function pointers suck horrifically and should never, ever, be used by anyone, ever again, except for the doomed souls bearing the Burning Standards of Hell C interoperation, because they cannot handle functions with state.

A std::function<void()> cannot, in the general case, be converted to a void(*)(). The only reason this works in the first example is because it happens to be a void(*)() originally.