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Design pattern: Flyweight

Description: "Use sharing to support a large number of fine-grained objects efficiently."

This pattern can be used with both classes and prototypes.

Flyweight objects store invariant state that can be shared between several objects, thus allowing more efficient representation of large number of objects that share that state. This allow those objects to only store the variant parts of the state.

Note that any object in Logtalk, independently of the role it plays (e.g. prototype or class), can also act as a flyweight object for its descendants. Static predicates that should be shared can simply be defined in the flyweight object and inherited by its descendants. Any dynamic predicates can be handled (i.e., asserted, accessed, and retracted) in either the flyweight object, if shared, or in self, if it may differ for each descendant.