Episode Nine: Erasing the Concrete

Type erasure is a technique that allows to store and operate objects of different types that fulfill a given concept. It can be seen as non-intrusively introducing an abstract base class to every type that provides a common interface. It turns a wide variety of types into one type.

Two big exponents of type erasure are Boost.Any [1] and Boost.Function [2]. Boost.Any is like C# and Java's Object base class, except it has value semantics. Boost.Function implements a generalized callback type that can be used to store arbitrary function pointers and function objects.

Episode Eight: The Curious Case of Recurring Template Pattern

The curiously recurring template pattern (CRTP) is an idiom in which a class X derives from a class template instantiation using X itself as template argument. It splits generic and concrete functionality by delegating to its derived class. This works because X is an incomplete type at the point of template instantiation, and it only works when the declaration of the base template does not use X as a complete type. Member function definitions, on the other side, are instantiated long after their declarations, allowing use of members of the derived class via the use of a static_cast.