Chapter 16. Templates and Generic Programming

CONTENTS

Section 16.1 Template Definitions	624
Section 16.2 Instantiation	636
Section 16.3 Template Compilation Models	643
Section 16.4 Class Template Members	647
Section 16.5 A Generic Handle Class	666
Section 16.6 Template Specializations	671
Section 16.7 Overloading and Function Templates	679
Chapter Summary	683
Defined Terms	683

Generic programming involves writing code in a way that is independent of any particular type. When we use a generic program we supply the type(s) or value(s) on which that instance of the program will operate. The library containers, iterators, and algorithms described in Part II are examples of generic programming. There is a single definition of each container, such as vector, but we can define many different kinds of vectors that differ by the element type that the vector contains.

Templates are the foundation of generic programming. We can, and have, used templates without understanding how they are defined. In this chapter we'll see how we can define our own template classes and functions.

Generic programming, like object-oriented programming, relies on a form of polymorphism. The polymorphism in OOP applies at run time to classes related by inheritance. We can write code that uses such classes in ways that ignore the type differences among the base and derived classes. As long as we use references or pointers to the base type, we can use the same code on objects of the base type or a type derived from that type.

Generic programming lets us write classes and functions that are polymorphic across unrelated types at compile time. A single class or function can be used to manipulate objects of a variety of types. The standard library containers, iterators, and algorithms are good examples of generic programming. The library defines each of the containers, iterators, and algorithms in a type-independent manner. We can use library classes and functions on most any kind of type. For example, we can define a vector of Sales_item objects even though the designers of vector could have had no knowledge of our application-specific class.

In C++, templates are the foundation for generic programming. A template is a blueprint or formula for creating a class or a function. For example, the standard library defines a single class template that defines what it means to be a vector. That template is used to generate any number of type-specific vector classesfor example, vector<int> or vector<string>. Part II showed how to use generic types and functions; this chapter shows how we can define our own templates.