PHP設計模式系列（二十一）：享元模式

享元模式

享元模式(Flyweight Pattern)：運用共享技術有效地支援大量細粒度對象的複用。系統隻使用少量的對象，而這些對象都很相似，狀态變化很小，可以實作對象的多次複用。由于享元模式要求能夠共享的對象必須是細粒度對象，是以它又稱為輕量級模式，它是一種對象結構型模式。

模式結構

享元模式包含如下角色：

• Flyweight: 抽象享元類
• ConcreteFlyweight: 具體享元類
• UnsharedConcreteFlyweight: 非共享具體享元類
• FlyweightFactory: 享元工廠類

結構圖

PHP代碼實作

<?php
/**
 * 享元模式
 */
abstract class Flyweight {
    abstract public function operation($state);
}

//具體享元角色
class ConcreteFlyweight extends Flyweight {
    private $state = null;
    public function __construct($state) {
        $this->state = $state;
    }
    public function operation($state) {
        var_dump('具體Flyweight:'.$state);
    }

}

//不共享的具體享元，用戶端直接調用
class UnsharedConcreteFlyweight extends Flyweight {
    private $state = null;
    public function __construct($state) {
        $this->state = $state;
    }
    public function operation($state) {
        var_dump('不共享的具體Flyweight:'.$state);
    }
}

//享元工廠角色
class FlyweightFactory {
    private $flyweights;
    public function __construct() {
        $this->flyweights = array();
    }
    public function getFlyweigth($state) {
        if (isset($this->flyweights[$state])) {
            return $this->flyweights[$state];
        } else {
            return $this->flyweights[$state] = new ConcreteFlyweight($state);
        }
    }
}

$f = new FlyweightFactory();
$a = $f->getFlyweigth('state A');
$a->operation("other state A");

$b = $f->getFlyweigth('state B');
$b->operation('other state B');

/* 不共享的對象，單獨調用 */
$u = new UnsharedConcreteFlyweight('state A');
$u->operation('other state A');
           

運作結果

string '具體Flyweight:other state A' (length=)
string '具體Flyweight:other state B' (length=)
string '不共享的具體Flyweight:other state A' (length=)