Summary

In this chapter, we have reviewed a classic object-oriented design pattern, the Template Method, as it applies to C++ programs. This pattern works in C++ as well as in any other object-oriented language, but C++ also has its own flavor of the Template Method—the non-virtual interface idiom. The advantages of this design pattern lead to a rather broad guideline—make all virtual functions private or protected. Be mindful, however, of the specifics of the destructors with regard to polymorphism. Here are the general guidelines for access (public vs private) to virtual functions:

1. Prefer to make interfaces nonvirtual, using the Template Method design pattern
2. Prefer to make virtual functions private
3. Only if derived classes need to invoke the base implementation of a virtual function, make the virtual function protected.
4. A base class destructor should be either public and virtual (if objects are deleted through the base class pointer) or protected...