Chapter 6. Inheritance and Object-Oriented Design

Object-oriented programming (OOP) has been the rage for almost two decades, so it's likely that you have some experience with the ideas of inheritance, derivation, and virtual functions. Even if you've been programming only in C, you've surely not escaped the OOP hoopla.

Still, OOP in C++ is probably a bit different from what you're used to. Inheritance can be single or multiple, and each inheritance link can be public, protected, or private. Each link can also be virtual or non-virtual. Then there are the member function options. Virtual? Non-virtual? Pure virtual? And the interactions with other language features. How do default parameter values interact with virtual functions? How does inheritance affect C++'s name lookup rules? And what about design options? If a class's behavior needs to be modifiable, is a virtual function the best way to do that?

This chapter sorts it all out. Furthermore, I explain what the different features in C++ really mean what you are really expressing when you use a particular construct. For example, public inheritance means "is-a," and if you try to make it mean anything else, you'll run into trouble. Similarly, a virtual function means "interface must be inherited," while a non-virtual function means "both interface and implementation must be inherited." Failing to distinguish between these meanings has caused C++ programmers considerable grief.

If you understand the meanings of C++'s various features, you'll find that your outlook on OOP changes. Instead of it being an exercise in differentiating between language features, it will become a matter of determining what you want to say about your software system. And once you know what you want to say, the translation into C++ is not terribly demanding.