Question

I’m writing a delegate class for educational purposes and have run into a little problem. The delegate must be able to call not only functions but also member methods of objects, which means that I need to store a pointer to a method:

void (classname::*methodPtr)(...);

And I need to store pointers to methods from different classes and with different argument lists. At first I just wanted to cast the method pointer to void *, but the compiler dies with an invalid cast error. Turns out that sizeof(methodPtr) == 8 (32-bit system here), but casts to unsigned long long also fail (same compiler error – invalid cast). How do I store the method pointer universally then?

I know it’s not safe – I have other safety mechanisms, please just concentrate on my question.

Answer 1

You don’t. You use run-time inheritance, if you need abstraction, and create a derived class which is templated on the necessities, or preferably, just create a plain old functor via the use of a function. Check out boost::bind and boost::function (both in the Standard for C++0x) as to how it should be done- if you can read them past all the macro mess, anyway.