FAQ 27.14 Should the inheritance graph of C hierarchies be tall or short?

FAQ 27.14 Should the inheritance graph of C++ hierarchies be tall or short?

The inheritance graph should be a forest of short trees.

When the inheritance graph is too tall, downcasts are common. This is because the type of the pointer is often sufficiently different from the type of the object that the desired member function is available only by downcasting the pointer. Also, the deeper the graph, the less likely that the inheritance relationships are proper. A tall graph is frequently a sign of an uninformed attempt at code reuse. Remember: inheritance is not for code reuse (see FAQ 8.12).

The type-safe philosophy espoused in this book discourages the unnecessary use of downcasting, even if downcasts are checked first.