PHP 装饰者模式

装饰者模式 Decorator Pattern ，动态地将责任附加到对象上。

若要扩展功能，装饰者提供了比继承更有弹性的替代方案。

<?php
//饮料抽象类
abstract class Beverage{
  public $description = 'Unknown Beverage';

  public function getDescription(){
    return $this->description;
  }

  public abstract function cost();
}

//调料抽象类
abstract class CondimentDecorator extends Beverage{
  //书中的JAVA代码里这里是一个抽象方法，PHP不允许这么做
  //public abstract function getDescription();
}

//饮料1
class Espresso extends Beverage{

  public function __construct(){
    $this->description = 'Espresso';
  }

  public function cost(){
    return 1.99;
  }
}

//饮料2
class HouseBlend extends Beverage{

  public function __construct(){
    $this->description = 'House Blend Coffee';
  }

  public function cost(){
    return 0.89;
  }
}

//调料1
class Mocha extends CondimentDecorator{
  public $beverage;

  public function __construct($beverage){
    $this->beverage = $beverage;
  }

  public function getDescription(){
    return $this->beverage->getDescription().', Mocha';
  }

  public function cost(){
    return 0.2 + $this->beverage->cost();
  }
}

//一杯普通的饮料
$beverage = new Espresso();
echo 'Description:'.$beverage->getDescription();
echo '<br/>Cost:'.$beverage->cost().'<br/>';

//一杯普通的饮料
$beverage2 = new HouseBlend();
//加一点调料
$beverage2 = new Mocha($beverage2);
echo 'Description:'.$beverage2->getDescription();
echo '<br/>Cost:'.$beverage2->cost().'<br/>';
//再多加一点调料
$beverage2 = new Mocha($beverage2);
echo 'Description:'.$beverage2->getDescription();
echo '<br/>Cost:'.$beverage2->cost().'<br/>';
//再多加一点调料
$beverage2 = new Mocha($beverage2);
echo 'Description:'.$beverage2->getDescription();
echo '<br/>Cost:'.$beverage2->cost().'<br/>';

输出

Description:Espresso   
Cost:1.99   
Description:House Blend Coffee, Mocha  
Cost:1.09  
Description:House Blend Coffee, Mocha, Mocha  
Cost:1.29  
Description:House Blend Coffee, Mocha, Mocha, Mocha  
Cost:1.49