享元模式，在定義上來說是共享物件，將相似的物件集中整理，減少記憶體上的使用，舉例來說每座島的大頭菜鈴錢價格都不同，有些朋友會送你大頭菜，但因為朋友太多了，所以需要有個地方集中放這些大頭菜，並且記錄起來，每個朋友都送你一組大頭彩，但你不能重複紀錄，不然你只收到一組大頭菜，帳上卻紀錄兩組，這樣就不好了。
什麼是享元模式#
核心概念#
享元模式核心概念
享元模式通過共享細粒度物件來有效地支援大量物件。它將物件的狀態分為內在狀態（可以共享）和外在狀態（不可共享），通過享元工廠來管理和重用物件實例，從而減少記憶體使用量。
使用時機#
適用情境
- 應用程式需要產生大量的物件
- 物件的大部分狀態都可以變為外在狀態
- 如果刪除物件的外在狀態，那麼可以用相對較少的共享物件取代很多組物件
- 應用程式不依賴於物件識別
UML#
實作#
定義享元介面（Flyweight Interface）#
享元介面設計
首先我們須要先定義享元介面，這個介面定義了所有享元物件必須實作的方法。在我們的大頭菜例子中，享元物件需要提供計算價格的功能。
FlyweightInterface.php#
/**
* Interface FlyweightInterface.
*/
interface FlyweightInterface
{
/**
* @return int
*/
public function calculatePrice(): int;
}
實作具體享元（Concrete Flyweight）#
具體享元設計
這是享元模式的核心類別，它實作了享元介面並儲存內在狀態。在我們的例子中，大頭菜享元紀錄了島嶼、鈴錢以及數量，並且提供了簡單的計算總價方法。
TurnipsFlyweight.php#
/**
* Class TurnipsFlyweight.
*/
class TurnipsFlyweight implements FlyweightInterface
{
/**
* @var string
*/
protected $island;
/**
* @var int
*/
protected $price;
/**
* @var int
*/
protected $count;
/**
* @param string $island
* @param int $price
* @param int $count
*/
public function __construct(string $island, int $price, int $count)
{
$this->island = $island;
$this->price = $price;
$this->count = $count;
}
/**
* @return int
*/
public function calculatePrice(): int
{
return $this->price * $this->count;
}
}
建立享元工廠（Flyweight Factory）#
享元工廠設計重點
享元工廠是享元模式的核心組件，主要負責建立、管理大頭菜共享物件，以及提供基本功能。它確保相同的島嶼只會建立一次物件，從而達到共享和節省記憶體的目的。
FlyweightFactory.php#
use Countable;
/**
* Class FlyweightFactory.
*/
class FlyweightFactory implements Countable
{
/**
* @var TurnipsFlyweight[]
*/
protected $turnips = [];
/**
* @param string $island
* @param int $price
* @param int $count
*/
public function get(string $island, int $price = 0, int $count = 0): TurnipsFlyweight
{
if (!isset($this->turnips[$island])) {
$this->turnips[$island] = new TurnipsFlyweight($island, $price, $count);
}
return $this->turnips[$island];
}
/**
* @return int
*/
public function calculateTotal(): int
{
$total = 0;
foreach ($this->turnips as $turnip) {
$total += $turnip->calculatePrice();
}
return $total;
}
/**
* @return int
*/
public function count(): int
{
return count($this->turnips);
}
}
技術補充說明#
Countable 介面說明
繼承 Countable 這個介面可以使用 PHP 的 count() 函數直接計算物件數量，因此需要實作 count() 方法。這提供了更直觀的 API 使用方式。
interface Countable {
abstract public count(): int
}
相關資源: PHP: Countable - Manual
測試#
測試目標#
測試清單
最後我們要對享元物件、工廠進行簡單的測試，驗證享元模式的共享機制和性能優化：
單個享元測試: 依序塞入享元，並且計算該次塞入的大頭菜跟紀錄所算出來的鈴錢是否相符
工廠管理測試: 大頭菜全部塞入後，所存入的筆數是否跟實際上相符
總計測試: 最後計算所有大頭菜的總鈴錢是否是正確的
測試程式碼#
FlyweightPatternTest.php#
/**
* Class FlyweightPatternTest.
*/
class FlyweightPatternTest extends TestCase
{
/**
* @var array
*/
protected $turnips = array(
'Island_A' => array('price' => 90, 'count' => 40),
'Island_B' => array('price' => 92, 'count' => 36),
'Island_C' => array('price' => 94, 'count' => 32),
'Island_D' => array('price' => 96, 'count' => 28),
'Island_E' => array('price' => 98, 'count' => 24),
'Island_F' => array('price' => 100, 'count' => 20),
'Island_G' => array('price' => 102, 'count' => 16),
'Island_H' => array('price' => 104, 'count' => 12),
'Island_I' => array('price' => 106, 'count' => 8),
'Island_J' => array('price' => 108, 'count' => 4),
'Island_K' => array('price' => 110, 'count' => 40),
);
/**
* @test
*/
public function test_flyweight()
{
$factory = new FlyweightFactory();
foreach ($this->turnips as $key => $value) {
$flyweight = $factory->get($key, $value['price'], $value['count']);
$total = $flyweight->calculatePrice();
$this->assertEquals($value['price'] * $value['count'], $total);
}
$this->assertCount(count($this->turnips), $factory);
$this->assertEquals(25520, $factory->calculateTotal());
}
}
測試結果#
最後測試的執行結果會獲得如下：
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 ✔ ✔ ✔
==> DataMapperTest ✔ ✔
==> DecoratorPatternTest ✔ ✔
==> DependencyInjectionTest ✔ ✔ ✔
==> FacadePatternTest ✔
==> FluentInterfaceTest ✔
==> FlyweightPatternTest ✔
Time: 00:00.030, Memory: 6.00 MB
OK (44 tests, 107 assertions)