C++ member function pointers in class and subclass

Question

I have one base class which holds a map for function pointers like this

typedef void (BaseClass::*event_t)();
class BaseClass {
    protected:
        std::map<std::string, event_t> events;
    public:
        // Example event
        void onFoo() {
            // can be added easily to the map
        }
};

Handling this works prefect, but now i want to make BaseClass an abstract base class to derive from like this:

 class SpecificClass : public BaseClass {
     public:
         void onBar() {
             // this is gonna be difficult!
         }
 };

Although i can access the map from SpecificClass i am not able to add onBar because the event_t type is only defined for the BaseClass! Is there any possibility (maybe with templates?) which does not lead to define the event_t for each class i will use...

(It is not neccessary to use templates! Any good/suitable approach would be nice.)

More background information:

This whole thing is for a text based RPG. My base class could be called Location and the specifc one any location e.g. CivicCenter. Each Location object subscribes to my EventSystem which notifies all neccessary objects when i fire an event. Therefore i want to store in a map some pointers to private functions holding the actions with their "name" like onSetOnFire (xD) as the key.

Answer 1

This can't be done with your current map as it stands. Think about what would happen if you could put a child method into the map. Then you could pull a pointer-to-child-member (masquerading as base) out of the map, call it on a base class instance pointer, and then how would it call a derived class on a base class instance which obviously couldn't work.

Would a polymorphic approach work?

Answer 2

Yes; stop using member pointers.

The more correct way of doing what you want is to have an event type and an object pointer. So an event fires on a specific object. The event type would be a non-member function (or a static member). It would be passed the object pointer. And it would call some actual member function of that object.

Nowadays, the event type could be a std/boost::function. However, since the function parameters have to stay the same type for all events, this doesn't really fix your problem. You can't call SpecificClass::onBar from a BaseClass pointer unless you do a cast to a SpecificClass. And the event calling function would not know to do this. So you still can't put SpecificClass::onBar in the std/boost::function object; you still need some standalone function to do the cast for you.

This all just seems to be a terrible use of polymorphism. Why does SpecificClass need to derive from BaseClass at all? Can't they just be two unrelated classes?