解释器模式/模板模式

这个模式应该是我们较为常用的,php/html模板系统中就会用到.

class A
{
    public function getInfo()
    {
        return ‘{{B.info}} or {{B.info}}‘;
    }
}

class B
{
    public function info()
    {
        return ‘this is info from B‘;
    }
}

class Interpreter
{
    private $a;

    public function __construct(A $a)
    {
        $this->a = $a;
    }

    public function execute()
    {
        $userInfo = $this->a->getInfo();
        if (preg_match_all(‘/\{\{B\.(.*?)\}\}/‘, $userInfo, $arr, PREG_SET_ORDER)) {
            $replace = array();
            foreach ($arr as $val) {
                $replace[] = $val[1];
            }

            $replace = array_unique($replace);

            $b = new B();
            foreach ($replace as $rep) {
                $userInfo = str_replace("{{B.{$rep}}}", call_user_func(array($b, $rep)), $userInfo);
            }
        }
        return $userInfo;
    }
}

// 调用
$a = new A();
$interpreter = new Interpreter($a);
echo $interpreter->execute();

在Interpreter类中初始化时创建了A的实例,其实也可以用继承来实现.

特点:
用于分析实体的关键元素,也就是说元素需要创建类的实例之后才是明确的.这点也是肯定的,否则,就没有解释器模式存在了.
需要预先知道大致对元素做何种解释.知道就可以switch/case.否则就是一个简单的if/else.如上例,我们就知道要替换B.info为对应内容.

所有的商品类在用户购买前,都需要给用户显示出最终支付的费用.但有些商品需要纳税,有些商品可能有打折.

abstract class Product
{
    protected $payPrice = 0;

    public final function setAdjustment()
    {
        $this->payPrice += $this->discount();
        $this->payPrice += $this->tax();
    }

    public function getPayPrice()
    {
        return $this->payPrice;
    }

    protected function discount()
    {
        return 0;
    }

    abstract protected function tax();
}

class CD extends Product
{
    public function __construct($price)
    {
        $this->payPrice = $price;
    }

    protected function tax()
    {
        return 0;
    }
}

class IPhone extends Product
{
    public function __construct($price)
    {
        $this->payPrice = $price;
    }

    protected function tax()
    {
        return $this->payPrice * 0.2;
    }

    protected function discount()
    {
        return -10;
    }

}

$cd = new CD(15);
$cd->setAdjustment();
echo $cd->getPayPrice();

$iphone = new IPhone(6000);
$iphone->setAdjustment();
echo $iphone->getPayPrice();