php 设计模式之 访问者

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1. 访问者模式

表示一个作用于某对象结构中的各元素的操作。它使你可以在不改变各元素的类的前提下定义作用于这些元素的新操作

2. 实列

interface ServiceVisitor {
    public function SendMsg(SendMessage $s);
    function PushMsg(PushMessage $p);
}

class AliYun implements ServiceVisitor {
    public function SendMsg(SendMessage $s) {
        echo '阿里云发送短信！', PHP_EOL;
    }
    public function PushMsg(PushMessage $p) {
        echo '阿里云推送信息！', PHP_EOL;
    }
}

class JiGuang implements ServiceVisitor {
    public function SendMsg(SendMessage $s) {
        echo '极光发送短信！', PHP_EOL;
    }
    public function PushMsg(PushMessage $p) {
        echo '极光推送短信！', PHP_EOL;
    }
}

interface Message {
    public function Msg(ServiceVisitor $v);
}

class PushMessage implements Message {
    public function Msg(ServiceVisitor $v) {
        echo '推送脚本启动：';
        $v->PushMsg($this);
    }
}

class SendMessage implements Message {
    public function Msg(ServiceVisitor $v) {
        echo '短信脚本启动：';
        $v->SendMsg($this);
    }
}

class ObjectStructure {
    private $elements = [];

    public function Attach(Message $element) {
        $this->elements[] = $element;
    }

    public function Detach(Message $element) {
        $position = 0;
        foreach ($this->elements as $e) {
            if ($e == $element) {
                unset($this->elements[$position]);
                break;
            }
            $position++;
        }
    }

    public function Accept(ServiceVisitor $visitor) {
        foreach ($this->elements as $e) {
            $e->Msg($visitor);
        }
    }

}

$o = new ObjectStructure();
$o->Attach(new PushMessage());
$o->Attach(new SendMessage());

$v1 = new AliYun();
$v2 = new JiGuang();

$o->Accept($v1);
$o->Accept($v2);