委托模式( Delegation)


1、模式定义

委托是对一个类的功能进行扩展和复用的方法。它的做法是:写一个附加的类提供附加的功能,并使用原来的类的实例提供原有的功能。 假设我们有一个 TeamLead 类,将其既定任务委托给一个关联辅助对象 JuniorDeveloper 来完成:本来 TeamLead 处理 writeCode 方法,Usage 调用 TeamLead 的该方法,但现在 TeamLead 将 writeCode 的实现委托给 JuniorDeveloper 的 writeBadCode 来实现,但 Usage 并没有感知在执行 writeBadCode 方法。

2、UML类图

Delegation-Design-Pattern-Uml

3、示例代码

Usage.php

<?php

namespace DesignPatterns\More\Delegation;

// 初始化 TeamLead 并委托辅助者 JuniorDeveloper
$teamLead = new TeamLead(new JuniorDeveloper());

// TeamLead 将编写代码的任务委托给 JuniorDeveloper
echo $teamLead->writeCode();

TeamLead.php

<?php

namespace DesignPatterns\More\Delegation;

/**
 * TeamLead类
 * @package DesignPatterns\Delegation
 * `TeamLead` 类将工作委托给 `JuniorDeveloper`
 */
class TeamLead
{
    /** @var JuniorDeveloper */
    protected $slave;

    /**
     * 在构造函数中注入初级开发者JuniorDeveloper
     * @param JuniorDeveloper $junior
     */
    public function __construct(JuniorDeveloper $junior)
    {
        $this->slave = $junior;
    }

    /**
     * TeamLead 喝咖啡, JuniorDeveloper 工作
     * @return mixed
     */
    public function writeCode()
    {
        return $this->slave->writeBadCode();
    }
}

JuniorDeveloper.php

<?php

namespace DesignPatterns\More\Delegation;

/**
 * JuniorDeveloper 类
 * @package DesignPatterns\Delegation
 */
class JuniorDeveloper
{
    public function writeBadCode()
    {
        return "Some junior developer generated code...";
    }
}

4、测试代码

Tests/DelegationTest.php

<?php

namespace DesignPatterns\More\Delegation\Tests;

use DesignPatterns\More\Delegation;

/**
 * DelegationTest 用于测试委托模式
 */
class DelegationTest extends \PHPUnit_Framework_TestCase
{
    public function testHowTeamLeadWriteCode()
    {
        $junior = new Delegation\JuniorDeveloper();
        $teamLead = new Delegation\TeamLead($junior);
        $this->assertEquals($junior->writeBadCode(), $teamLead->writeCode());
    }
}

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