Function Templates

Contemporary C++ compilers implement one of the newer C++ additions: function templates. A function template is a generic function description; that is, it defines a function in terms of a generic type for which a specific type, such as int or double, can be substituted. By passing a type as a parameter to a template, you cause the compiler to generate a function for that particular type. Because templates let you program in terms of a generic type instead of a specific type, the process is sometimes termed generic programming. Because types are represented by parameters, the template feature is sometimes referred to as parameterized types. Let’s see why such a feature is useful and how it works.

Earlier Listing 8.4 defined a function that swapped two int values. Suppose you want to swap two double values instead. One approach is to duplicate the original code but replace each int with double. If you need to swap two char values, you can use the same technique again. Still, it’s wasteful of your valuable time to have to make these petty changes, and there’s always the possibility of making an error. If you make the changes by hand, you might overlook an int. If you do a global search-and-replace to substitute, say, double for int, you might do something such as converting