overloading.cpp

#include <functional>
#include <string>

int foo (int a)
{
    return a;
}

void foo (std::string s) {}

int main()
{
    std::function<int(int)> func = foo;
}

// error: conversion from '<unresolved overloaded function type>' to non-scalar type 'std::function<int(int)>' requested