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Design pattern: Template Method

Description: "Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure."

This pattern can be used with both classes and prototypes.

The key for implementing this pattern is the message to self control construct, (::)/1. It allows a predicate implementing an algorithm to call the predicates implementing the algorithm steps defined in descendant objects. It also allows easy definition of default definitions for the algorithm steps that can be inherited, redefined, or specialized in the descendant objects. The predicates implementing the algorithm steps are often declared as protected.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the design pattern sample implementation:

logtalk_load(design_patterns('behavioral/template_method/loader')).

Print the steps for a car trip:

travel_by_car::journey.

<!-- Rent a car Put book, pajamas, and toothbrush in luggage Drive car to destination Put book and pajamas in nightstand and toothbrush in bathroom

true. -->

Print the steps for a airplane trip:

travel_by_airplane::journey.

<!-- Make a flight reservation Put book, pajamas, and toothbrush in luggage Check luggage weight against airline policy Go to the airport and board the airplane Put book and pajamas in nightstand and toothbrush in bathroom

true. -->