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The Visitor [1] design pattern is one of the twenty-three well-known Gang of Four design patterns that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse.
The single-serving visitor pattern should be used when visitors do not need to remain in memory. This is often the case when visiting a hierarchy of objects (such as when the visitor pattern is used together with the composite pattern) to perform a single task on it, for example counting the number of cameras in a 3D scene.
The visitor pattern solves this by factoring out the operation (pretty printing) to a separate class, which specializes in just pretty printing. So if you have many related types, and feel the urge to add more and more operations to (almost) every one of them, consider applying the Visitor pattern. --Objarni 10:57, 9 April 2012 (UTC)
In software engineering, a software design pattern or design pattern is a general, reusable solution to a commonly occurring problem in many contexts in software design. [1] A design pattern is not a rigid structure to be transplanted directly into source code.
Design Patterns: Elements of Reusable Object-Oriented Software (1994) is a software engineering book describing software design patterns. The book was written by Erich Gamma , Richard Helm , Ralph Johnson , and John Vlissides , with a foreword by Grady Booch .
The observer design pattern is a behavioural pattern listed among the 23 well-known "Gang of Four" design patterns that address recurring design challenges in order to design flexible and reusable object-oriented software, yielding objects that are easier to implement, change, test and reuse.
The indirection pattern supports low coupling and reuses potential between two elements by assigning the responsibility of mediation between them to an intermediate object. An example of this is the introduction of a controller component for mediation between data (model) and its representation (view) in the model-view-controller pattern.
In software engineering, structural design patterns are design patterns that ease the design by identifying a simple way to realize relationships among entities. Examples of Structural Patterns include: Adapter pattern: 'adapts' one interface for a class into one that a client expects Adapter pipeline: Use multiple adapters for debugging ...