Visitor

Intent, Motivation, Applicability, Structure, Participants, Collaborations, Consequences, Implementation, Sample Code, Known Uses, Related Patterns

Collaborations

• A client that uses the Visitor pattern must create a ConcreteVisitor object and then traverse the object structure, visiting each element with the visitor.
• When an element is visited, it calls the Visitor operation that corresponds to its class. The element supplies itself as an argument to this operation to let the visitor access its state, if necessary.

  The following interaction diagram illustrates the collaborations between an object structure, a visitor, and two elements:

  

Collaborations of Abstract Factory, Adapter, Bridge, Builder, Chain of Responsibility, Command, Composite, Decorator, Facade, Factory Method, Flyweight, Interpreter, Iterator, Mediator, Memento, Observer, Prototype, Proxy, Singleton, State, Strategy, Template Method, Visitor