FAQ 28.09 What s the difference between a homogeneous and a heterogeneous container?

FAQ 28.09 What's the difference between a homogeneous and a heterogeneous container?

The elements of a homogeneous container are all of the same type; the elements of a heterogeneous container can be of different types.

Containers come in many shades of gray. Generally speaking, the more heterogeneous the element types are, the less type safe the container is. For example, the ultimate heterogeneous container is a container of void* in which the various elements could point to objects of any type. Even though this seems to optimize flexibility, in practice such containers are nearly worthless. In particular, putting things into such a container is easy (any object of any type can be inserted), but when an element is removed, the user of the container knows nothing about the element's type.

A more useful form of heterogeneous container is one that requires its elements to point to objects derived from some specific base class, often an ABC. This base class typically has all or nearly all the member functions provided by the actual objects referenced by the container. For example, one might have a list of Shape* where the actual referents might be objects of class Square, Circle, Hexagon, and so on.

Note that the based object approach (see the previous FAQ) is another form of heterogeneous container.