Summary

We have examined a rather convoluted design pattern that combines both sides of C++—generic programming (templates) and object-oriented programming (inheritance). True to its name, the Curiously Recurring Template Pattern creates a circular loop, where the derived class inherits the interface and the implementation from the base class, while the base class has access to the interface of the derived class through the template parameters. CRTP has two main use modes—true static polymorphism, or static interface, where the object is primarily accessed as the base type, and expanding the interface, or delegation, where the derived class is accessed directly but the implementation uses CRTP to provide common functionality. The latter can vary from a simple addition of one or two methods to a complex task of composing the interfaces of derived classes from multiple building blocks or policies.

The next chapter introduces an idiom that makes use of the pattern we...