Why inheritance hierarchies are inflexible

The idea that Players, Enemies, Missiles, and Medics should all derive from one base object is very common to programmers new to object-oriented programming. It makes a lot of sense on paper that if you have a Raider and a SuperRaider, one should inherit from the other. I believe this comes from how inheritance is taught. When you are first learning about inheritance, you will almost always see a picture similar to this:

Figure 3.1 - A typical inheritance diagram when learning to program

Many introductory programming courses are so focused on the mechanics of inheritance that they forget to tell you how to use it properly. A picture like the one above makes it easy to understand that ITWorker is an Employee, which is a Person. However, once you go beyond the mechanics, it is time to learn how to use inheritance correctly. This is why books on design patterns exist.

Inheritance is a powerful tool that lets us extend classes by adding members and methods...