Handling unrelated types generically with the type erasure idiom

Polymorphism (and more specifically runtime polymorphism in C++) allows us to treat hierarchies of classes in a generic way. However, there are cases when we want to do the same but with classes that do not inherit from a common base class. This can happen when we do not own the code or, for various reasons, cannot change the code to create a hierarchy. This process of utilizing unrelated types that have some certain members (functions or variables) for given tasks (and only use those common members) is called duck typing. A simple solution to this problem is to build a hierarchy of wrapper classes, one for each class that we want to handle generically. This has drawbacks because there is a lot of boilerplate code and every time a new class needs to be handled in the same manner, a new wrapper must be created. The alternative to this approach is an idiom known as type erasure. The term refers to the fact that information...