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	Template Design

In software engineering, the template method pattern is a design pattern. It is a so-called behavioral pattern, and is unrelated to C++ templates.

A template method defines the program skeleton of an algorithm. The algorithm itself is made abstract, and the subclasses override the abstract methods to provide concrete behavior.

First a class is created that provides the basic steps of an algorithm design. These steps are implemented using abstract methods. Later on, subclasses change the abstract methods to implement real actions. Thus the general algorithm is saved in one place but the concrete steps may be changed by the subclasses.

The template method thus manages the larger picture of task semantics, and more refined implementation details of selection and sequence of methods. This larger picture calls abstract and non-abstract methods for the task at hand. The non-abstract methods are completely controlled by the Template method. The expressive power and degrees of freedom occur in abstract methods that may be implemented in subclasses. Some or all of the abstract methods can be specialized in the subclass, the abstract method is the smallest unit of granularity, allowing the writer of the subclass to provide particular behavior with minimal modifications to the larger semantics. In contrast the template method need not be changed and is not an abstract operation and thus may guarantee required steps before and after the abstract operations. Thus the template method is invoked and as a consequence the subordinate non-abstract methods and abstract methods are called in the correct sequence.