Using abstract base classes
If we are to implement our design correctly, then we have to be certain that all of our derived classes have a declaration and definition for each of the functions we want to access through the base class pointer. We can ensure this by making GameObject an abstract base class. An abstract base class cannot be initialized itself; its purpose is to dictate the design of derived classes. This gives us reusability as we know that any object we derive from GameObject will immediately work in the overall scheme of the game.
An abstract base class is a class that contains at least one pure virtual function. A pure virtual function is a function that has no definition and must be implemented in any derived classes. We can make a function pure virtual by suffixing it with =0.
