範例：三隻小豬（原型模式）

2020-10-11

Example

情境：三隻小豬想要蓋房子

首先是牆壁，可以選擇不同的建材

<?php

namespace App\PrototypePattern\Building;

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

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

接著是房子

<?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;
    }
}

接著豬大哥用 稻草 (straw) ，蓋了間稻草屋

<?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，豬大哥很得意自己對房子的設計，
詢問弟弟們要不要直接拷貝一間。

需求一：拷貝豬大哥的稻草屋

兩個弟弟想了想，拷貝大哥的房子，好像是個省事的方法，
但二弟想用木材 (wood)，三弟想用磚塊 (bricks) 來蓋房子。

決定拷貝稻草屋的弟弟們

<?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
        ];
    }
}

這時發生了件很尷尬的事情，
當豬二哥選用木材當建材時，大哥的稻草屋就變成木頭屋了…
而豬小弟選用磚塊當建材時，兩個哥哥們的房子就變成磚頭屋了…

導演表示，這樣故事沒辦法進行下去，請我們修改一下。

需求二：讓弟弟們對建材的修改，不會影響到哥哥

修改Building中的clone()方法，讓拷貝時能重新創建牆壁

<?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;
    }
}

不用修改原本的程式碼

<?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
        ];
    }
}

後來弟弟們改用其他建材時，就不會影響到原本哥哥的房子了。

這就是淺複製 (Shallow Copy) 與 深複製 (Deep Copy) 的不同。

後來三隻小豬跑去開建設公司，又是另一個故事了。

ʕ •ᴥ•ʔ：一開始clone()方法能直接使用，是因為PHP的魔術方法__clone()唷！

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