State Pattern

Intent: Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.

See also: Strategy Pattern, Dynamic Classification, Run And Return Successor, Context Parameter

Duality Between State And Class gives a more philosophical discussion of why an object's "state" deserves to be modeled in a separate class.

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In Chapter 9 of Pattern Languages Of Program Design volume three, Paul Dyson and Bruce Anderson present seven "state" patterns in a Pattern Language, explaining the costs and benefits of various implementation strategies of this pattern. (Category Groups Of Patterns)

See also(?): Client State

Category Pattern | Category Behavioral Patterns

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