why can't I cast a pointer to Derived class member function to the same but of class Base?

Question

To me it looks perfectly safe to cast a void(Derived::*)() to a void(Base::*)(), like in this code:

#include 
#incl         


        

Answer 1

You need to use a std::function. This can be any member of any class, a lambda, a free function, a function object, whatever you need, which is super convenient.

#include 
#include 
using namespace std;
struct Base{
    std::function any_method;
    void call_it(){
        any_method();
    }
};
struct Derived: public Base{
    void a_method(){
        cout<<"method!"<a_method(); };
    a.call_it();
}

Here you can see that the actual implementation of any_method is totally abstracted from struct Base, and I can supply a function object that does anything, at all- including conveniently calling a Derived method.