Detailed explanation of the decorator pattern of PHP design patterns

<?php

/*
 * 装饰模式
 */

abstract class Beverage
{
    public $_name;

    abstract public function Cost();
}

// 被装饰者类
class Coffee extends Beverage
{
    public function construct()
    {
        $this->_name = &#39;Coffee&#39;;
    }

    public function Cost()
    {
        return 1.00;
    }
}

// 以下三个类是装饰者相关类
class CondimentDecorator extends Beverage //装饰类
{
    public function construct()
    {
        $this->_name = &#39;Condiment&#39;;
    }

    public function Cost()
    {
        return 0.1;
    }
}

class Milk extends CondimentDecorator //牛奶 配料 --装饰者
{
    public $_beverage;

    public function construct($beverage)
    {
        if ($beverage instanceof Beverage) {
            $this->_beverage = $beverage;
        } else
            exit(&#39;Failure&#39;);
    }

    public function Cost()
    {
        return $this->_beverage->Cost() + 0.2;
    }
}

class Sugar extends CondimentDecorator //糖 配料 --装饰者
{
    public $_beverage;

    public function construct($beverage)
    {
        $this->_name = &#39;Sugar&#39;;
        if ($beverage instanceof Beverage) {
            $this->_beverage = $beverage;
        } else {
            exit(&#39;Failure&#39;);
        }
    }

    public function Cost()
    {
        return $this->_beverage->Cost() + 0.2;
    }
}

// Test Case
//1.拿杯咖啡
$coffee = new Coffee();

//2.加点牛奶
$coffee = new Milk($coffee);

//3.加点糖
$coffee = new Sugar($coffee);

echo $coffee->Cost();
echo $coffee->_name;