VS2012下std::function的BUG解决办法

VS2012版本下std::function存在问题，链接：https://stackoverflow.com/questions/13096162/stdfunction-not-compiling-in-vs2012

#include <iostream>
#include <functional>

struct Foo {
    Foo(int num) : num_(num) {}
    void print_add(int i) const { std::cout << num_+i << '\n'; }
    int num_;
};

int main()
{
    // store a call to a member function
    std::function<void(const Foo&, int)> f_add_display = std::mem_fn(&Foo::print_add);
    Foo foo(314159);
    f_add_display(foo, 1);
}