Day38. 范例：三只小猪 （原型模式）

本文同步更新於blog

情境：三只小猪想要盖房子

• 首先是墙壁，可以选择不同的建材

<?php

namespace App\PrototypePattern\Building;

class Wall
{
    /**
     * @var string
     */
    public $material;

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

• 接着是房子

<?php

namespace App\PrototypePattern\Building;

use App\PrototypePattern\Building\Wall;

class Building
{
    /**
     * @var string
     */
    public $name;

    /**
     * @var Wall
     */
    public $wall;

    /**
     * @param Wall $wall
     * @param string $name
     */
    public function __construct(Wall $wall, string $name = 'unnamed')
    {
        $this->wall = $wall;
        $this->name = $name;
    }
}

• 接着猪大哥用稻草 (straw)，盖了间稻草屋

<?php

namespace App\PrototypePattern\Building;

use App\PrototypePattern\Building\Building;
use App\PrototypePattern\Building\Wall;

class Program
{
    /**
     * @return array
     */
    public function run()
    {
        //firstBuilding
        $strawWall = new Wall('straw');
        $firstBuilding = new Building($strawWall, 'oldestPigHouse');

        dump($firstBuilding->name); // oldestPigHouse
        dump($firstBuilding->wall->material); // straw
    }
}

完成後，猪大哥很得意自己对房子的设计，
询问弟弟们要不要直接拷贝一间。

需求一：拷贝猪大哥的稻草屋

两个弟弟想了想，拷贝大哥的房子，好像是个省事的方法，
但二弟想用木材 (wood)，三弟想用砖块 (bricks) 来盖房子。

• 决定拷贝稻草屋的弟弟们

<?php

namespace App\PrototypePattern\Building;

use App\PrototypePattern\Building\Building;
use App\PrototypePattern\Building\Wall;

class Program
{
    /**
     * @return array
     */
    public function run()
    {
        //firstBuilding
        $strawWall = new Wall('straw');
        $firstBuilding = new Building($strawWall, 'oldestPigHouse');

        //secondBuilding
        $secondBuilding = clone $firstBuilding;
        $secondBuilding->name = 'middlePigHouse';
        $secondBuilding->wall->material = 'wood';

        //thirdBuilding
        $thirdBuilding = clone $firstBuilding;
        $thirdBuilding->name = 'youngestPigHouse';
        $thirdBuilding->wall->material = 'bricks';

        dump($firstBuilding->name); // oldestPigHouse
        dump($firstBuilding->wall->material); // bricks

        dump($secondBuilding->name); // middlePigHouse
        dump($secondBuilding->wall->material); // bricks

        dump($thirdBuilding->name); // youngestPigHouse
        dump($thirdBuilding->wall->material); // bricks

        return [
            'firstBuilding' => $firstBuilding,
            'secondBuilding' => $secondBuilding,
            'thirdBuilding' => $thirdBuilding
        ];
    }
}

这时发生了件很尴尬的事情，
当猪二哥选用木材当建材时，大哥的稻草屋就变成木头屋了...
而猪小弟选用砖块当建材时，两个哥哥们的房子就变成砖头屋了...

导演表示，这样故事没办法进行下去，请我们修改一下。

需求二：让弟弟们对建材的修改，不会影响到哥哥

• 修改Building中的clone()方法，让拷贝时能重新创建墙壁

<?php

namespace App\PrototypePattern\Building;

use App\PrototypePattern\Building\Wall;

class Building
{
    /**
     * @var string
     */
    public $name;

    /**
     * @var Wall
     */
    public $wall;

    /**
     * @param Wall $wall
     * @param string $name
     */
    public function __construct(Wall $wall, string $name = 'unnamed')
    {
        $this->wall = $wall;
        $this->name = $name;
    }

    public function __clone()
    {
        $this->wall = clone $this->wall;
    }
}

• 不用修改原本的程序码

<?php

namespace App\PrototypePattern\Building;

use App\PrototypePattern\Building\Building;
use App\PrototypePattern\Building\Wall;

class Program
{
    /**
     * @return array
     */
    public function run()
    {
        //firstBuilding
        $strawWall = new Wall('straw');
        $firstBuilding = new Building($strawWall, 'oldestPigHouse');

        //secondBuilding
        $secondBuilding = clone $firstBuilding;
        $secondBuilding->name = 'middlePigHouse';
        $secondBuilding->wall->material = 'wood';

        //thirdBuilding
        $thirdBuilding = clone $firstBuilding;
        $thirdBuilding->name = 'youngestPigHouse';
        $thirdBuilding->wall->material = 'bricks';

        dump($firstBuilding->name); // oldestPigHouse
        dump($firstBuilding->wall->material); // straw

        dump($secondBuilding->name); // middlePigHouse
        dump($secondBuilding->wall->material); // wood

        dump($thirdBuilding->name); // youngestPigHouse
        dump($thirdBuilding->wall->material); // bricks

        return [
            'firstBuilding' => $firstBuilding,
            'secondBuilding' => $secondBuilding,
            'thirdBuilding' => $thirdBuilding
        ];
    }
}

後来弟弟们改用其他建材时，就不会影响到原本哥哥的房子了。

这就是浅复制 (Shallow Copy) 与深复制 (Deep Copy) 的不同。

後来三只小猪跑去开建设公司，又是另一个故事了。

最後附上类别图：

（注：若不熟悉 UML 类别图，可参考UML类别图说明。）

ʕ •ᴥ•ʔ：一开始clone()方法能直接使用，是因为PHP的魔术方法__clone()唷！