c++ pointers to operators

问题:

I want to write a pointer in c++ (or in c++0x), that will points to a operator of a class lets say A or B. Is there any method to do it?

Of course there is a syntax like

int (A::*_p) ();

but it doesn't solve this problem. I want to make general pointer, not specifying the base class for it - only pointer for "operator function"

#include <thread>
#include <iostream>

using namespace std;

class A
{
public:
    int operator()()
    {
        return 10;
    }
};

class B
{
public:
    int operator()()
    {
        return 11;
    }
};

int main()
{
 A a;
 int (*_p) ();
 _p = a.operator();
 cout << _p();

 B b;
 _p = b.operator();
 cout << _p();
}

回答1:

No, you can't do this. The class type is a part of the type of the operator member function.

The type of A::operator()() is different from the type of B::operator()(). The former is of type int (A::*)() while the latter is of type int (B::*)(). Those types are entirely unrelated.

The closest you can get is by using something like the C++0x polymorphic function wrapper function (found in C++0x, C++ TR1, and Boost) and by using bind to bind the member function pointer to a class instance:

std::function<int()> _p;

A a;
_p = std::bind(&A::operator(), a);
std::cout << _p();

B b;
_p = std::bind(&B::operator(), b);
std::cout << _p();