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b8381e5a60
Previous example was simply implementing a strategy pattern. A key problem is that WebService made clear that it did no actual output of its own - it handed it off to 'decorators'. A decorator should always wrap a class that already has its own complete, self-contained functionality. In this way, they only enhance / modify it. An instance that is non-decorated should work fully by itself. Note the distinguishing difference between this and sub-classing - here the enhancement is added dynamically, at runtime, and to one instance. With sub-classing, the enhancement is added at compile / parse time, and is applied to all instances / uses of the subclass.
75 lines
1.5 KiB
PHP
75 lines
1.5 KiB
PHP
<?php
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namespace DesignPatterns;
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/**
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* Decorator pattern
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*
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* Purpose:
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* to dynamically add new functionality to class instances
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*
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* Examples:
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* - Zend Framework: decorators for Zend_Form_Element instances
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* - Web Service Layer: Decorators JSON and XML for a REST service (in this case, only one of these should be allowed of
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* course)
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*
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*/
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interface Renderer
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{
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public function renderData();
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}
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class Webservice implements Renderer
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{
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protected $_data;
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public function __construct($data)
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{
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$this->_data = $data;
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}
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public function renderData()
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{
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return $this->_data;
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}
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}
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abstract class Decorator
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{
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protected $_wrapped;
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public function __construct($wrappable)
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{
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$this->_wrapped = $wrappable;
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}
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}
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class RenderInJson extends Decorator implements Renderer
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{
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public function renderData()
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{
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$output = $this->_wrapped->renderData();
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return json_encode($output);
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}
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}
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class RenderInXml extends Decorator implements Renderer
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{
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public function renderData()
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{
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$output = $this->_wrapped->renderData();
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// do some fany conversion to xml from array ...
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return simplexml_load_string($output);
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}
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}
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// Create a normal service
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$service = new Webservice(array('foo' => 'bar'));
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// Wrap service with a JSON decorator for renderers
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$service = new RenderInJson($service);
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// Our Renderer will now output JSON instead of an array
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echo $service->renderData();
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