18.2. Class Templates

It’s possible to understand the concept of a stack (a data structure into which we insert items only at the top and retrieve those items only from the top in last-in, first-out order) independent of the type of the items being placed in the stack. However, to instantiate a stack, a data type must be specified. This creates a nice opportunity for software reusability—as you already saw with the stack container adapter in Section 15.7.1. Here, we define a stack generically then use type-specific versions of this generic stack class.

Class templates are called parameterized types, because they require one or more type parameters to specify how to customize a generic class template to form a class-template specialization. To produce many specializations you write only one class-template definition (as we’ll do shortly). When a particular specialization is needed, you use a concise, simple notation, and the compiler writes the specialization source code. One Stack class template, for example, could thus become the basis for creating many Stack class-template specializations (such as “Stack of doubles,” “Stack of ints,” “Stack of Employees,” “Stack of Bills,” etc.) used in a program.