MFC Programmer's SourceBook : Thinking in C++
Bruce Eckel's Thinking in C++, 2nd Ed Contents | Prev | Next

Summary

Both inheritance and composition allow you to create a new type from existing types, and both embed subobjects of the existing types inside the new type. Typically, however, you use composition to reuse existing types as part of the underlying implementation of the new type and inheritance when you want to reuse the interface as well as the implementation. If the derived class has the base-class interface, it can be upcast to the base, which is critical for polymorphism as you’ll see in the next chapter.

Although code reuse through composition and inheritance is very helpful for rapid project development, you’ll generally want to redesign your class hierarchy before allowing other programmers to become dependent on it. Your goal is a hierarchy where each class has a specific use and is neither too big (encompassing so much functionality that it’s unwieldy to reuse) nor annoyingly small (you can’t use it by itself or without adding functionality). Your finished classes should themselves be easily reused.

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