The Non-Virtual Interface

The implementation of the dynamically customizable parts of the templated algorithm is usually done with virtual functions. For a general Template Method pattern, this is not a requirement, but in C++, we rarely need another way. Now, we are going to focus specifically on using the virtual functions and improving on what we have learned.

Virtual functions and access

Let’s start with a general question—should virtual functions be public or private? The textbook object-oriented design style uses public virtual functions, so we often make them public without a second thought. Within the Template Method, this practice needs to be reevaluated—a public function is part of the class interface. In our case, the class interface includes the entire algorithm, and the framework we put in place in the base class. This function should be public, but it is also non-virtual. The customized implementations of some parts of the algorithm were never...