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#354 Add maven model for feature toggle design pattern

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Joseph McCarthy
2016-01-25 21:14:24 +00:00
parent cf10bd1d05
commit d7526fc7c0
86 changed files with 1165 additions and 270 deletions
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visitor/index.md
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@@ -10,22 +10,24 @@ tags:
- Gang Of Four
---
**Intent:** Represent an operation to be performed on the elements of an object
## Intent
Represent an operation to be performed on the elements of an object
structure. Visitor lets you define a new operation without changing the classes
of the elements on which it operates.
![alt text](./etc/visitor_1.png "Visitor")
**Applicability:** Use the Visitor pattern when
## Applicability
Use the Visitor pattern when
* an object structure contains many classes of objects with differing interfaces, and you want to perform operations on these objects that depend on their concrete classes
* many distinct and unrelated operations need to be performed on objects in an object structure, and you want to avoid "polluting" their classes with these operations. Visitor lets you keep related operations together by defining them in one class. When the object structure is shared by many applications, use Visitor to put operations in just those applications that need them
* the classes defining the object structure rarely change, but you often want to define new operations over the structure. Changing the object structure classes requires redefining the interface to all visitors, which is potentially costly. If the object structure classes change often, then it's probably better to define the operations in those classes
**Real world examples:**
## Real world examples
* [Apache Wicket](https://github.com/apache/wicket) component tree, see [MarkupContainer](https://github.com/apache/wicket/blob/b60ec64d0b50a611a9549809c9ab216f0ffa3ae3/wicket-core/src/main/java/org/apache/wicket/MarkupContainer.java)
**Credits**
## Credits
* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)