組合模式 Composite Pattern

組合模式,一種將物件一個一個處理,並且最後組合起來的模式,可以想像剛買到大頭菜時的夢想,經過每次漲跌所帶來的希望與絕望,究竟是充滿絕望的遞減型呢?還是致富關鍵的三期型呢?每次的價格異動,都代表著價格物件,最終賣出的鈴錢價格,是經過許多鈴錢價格物件所算出來的。

UML

UML

實作

首先我們要先定義組合介面,用來套用在每個功能物件上。

TurnipsInterface.php

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/**
* Interface TurnipsInterface.
*/
interface TurnipsInterface
{
public function calculatePrice(): int;
}

再來建立大頭菜上漲(Price up)以及下跌(Price down)的物件,並且套用介面 Interface,其功能是把漲跌幅丟進去,用來紀錄當次的漲跌幅。

PriceUp.php

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/**
* Class PriceUp.
*/
class PriceUp implements TurnipsInterface
{
/**
* @var int
*/
protected $price;

/**
* PriceDown constructor.
*
* @param int $price
*/
public function __construct(int $price)
{
$this->price = $price;
}

/**
* @return int
*/
public function calculatePrice(): int
{
return $this->price;
}
}

PriceDown.php

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/**
* Class PriceDown.
*/
class PriceDown implements TurnipsInterface
{
/**
* @var int
*/
protected $price;

/**
* PriceDown constructor.
*
* @param int $price
*/
public function __construct(int $price)
{
$this->price = $price;
}

/**
* @return int
*/
public function calculatePrice(): int
{
return - $this->price;
}
}

最後建立大頭菜,賦予起始價格以及數量,然後可以賦予每次價格漲跌幅的物件,然後根據每個漲跌幅物件,來計算最終的鈴錢價格。

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/**
* Class Turnips.
*/
class Turnips implements TurnipsInterface
{
/**
* @var int
*/
protected $price;

/**
* @var int
*/
protected $count;

/**
* @var TurnipsInterface[]
*/
protected $elements = [];

/**
* Turnips constructor.
*
* @param int $price
* @param int $count
*/
public function __construct(int $price, int $count)
{
$this->price = $price;
$this->count = $count;
}

/**
* @return int
*/
public function calculatePrice(): int
{
$_price = $this->price;
foreach ($this->elements as $element) {
$_price += $element->calculatePrice();
}

return $_price * $this->count;
}

/**
* @param TurnipsInterface $element
*/
public function addElement(TurnipsInterface $element)
{
array_push($this->elements, $element);
}
}

測試

最後我們需要將大頭菜組合模式來寫些測試驗證一下,主要是測試鈴錢價格上漲物件、鈴錢價格下跌物件是否能夠正常運作,再來實際組裝起來再各別計算一次。

  1. 測試鈴錢價格上漲物件是否能夠正常運作。
  2. 測試鈴錢價格下跌物件是否能夠正常運作。
  3. 測試鈴錢價格上漲物件、鈴錢價格下跌物件實際組裝起來再各別計算一次。

CompositePatternTest.php

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/**
* Class CompositePatternTest.
*/
class CompositePatternTest extends TestCase
{
/**
* 測試鈴錢價格上漲物件是否能夠正常運作。
*
* @test
*/
public function test_price_up()
{
$price = new PriceUp(20);
$this->assertEquals(20, $price->calculatePrice());
}

/**
* 測試鈴錢價格下跌物件是否能夠正常運作。
*
* @test
*/
public function test_price_down()
{
$price = new PriceDown(20);
$this->assertEquals(-20, $price->calculatePrice());
}

/**
* 測試鈴錢價格上漲物件、鈴錢價格下跌物件實際組裝起來再各別計算一次。
*
* @test
*/
public function test_price_up_and_down()
{
$turnips = new Turnips(100, 40);
$this->assertEquals(4000, $turnips->calculatePrice());

$turnips->addElement(new PriceUp(20));
$this->assertEquals(4800, $turnips->calculatePrice());

$turnips->addElement(new PriceDown(30));
$this->assertEquals(3600, $turnips->calculatePrice());
}
}

最後測試的執行結果會獲得如下:

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PHPUnit Pretty Result Printer 0.28.0 by Codedungeon and contributors.
==> Configuration: ~/php-design-pattern/vendor/codedungeon/phpunit-result-printer/src/phpunit-printer.yml

PHPUnit 9.2.6 by Sebastian Bergmann and contributors.


==> AbstractFactoryTest ✔ ✔ ✔ ✔
==> BuilderPatternTest ✔ ✔ ✔ ✔
==> FactoryMethodTest ✔ ✔ ✔ ✔
==> PoolPatternTest ✔ ✔
==> PrototypePatternTest ✔ ✔
==> SimpleFactoryTest ✔ ✔ ✔ ✔
==> SingletonPatternTest ✔
==> StaticFactoryTest ✔ ✔ ✔ ✔ ✔
==> AdapterPatternTest ✔ ✔
==> BridgePatternTest ✔ ✔ ✔
==> CompositePatternTest ✔ ✔ ✔

Time: 00:00.050, Memory: 6.00 MB

OK (34 tests, 81 assertions)

完整程式碼

設計模式不難,找回快樂而已,以大頭菜為例。

參考文獻