桥接模式

<?php
#Bridge（桥接）模式：将抽象部分与它的实现部分分离，使它们都可以独立的变化



//实现站内、eamil都能发送普通信息和紧急信息 
//抽象类,定义信息 
abstract class info{
    protected $send = null;
    public function __construct($send){
        $this->send = $send;
    }
    abstract public function msg($content);
    public function send($to,$content){
        $content = $this->msg($content);
        $this->send->send($to,$content);
    }
}

class zn{
    public function send($to,$content){
        echo "站内给",$to,"内容是：",$content;
    }
}

class email{
    public function send($to,$content){
        echo "email给",$to,"内容是：",$content;
    }
}
class sms{
    public function send($to,$content){
        echo "sms给",$to,"内容是：",$content;
    }
}

//扩展抽象类
class commoninfo extends info{
    public function msg($content){
        return "普通".$content;
    }
}
class warninfo extends info{
    public function msg($content){
        return "紧急".$content;
    }
}
class dangerinfo extends info{
    public function msg($content){
        return "特级".$content;
    }
}

$commoninfo = new commoninfo(new zn());
$commoninfo->send("小明","吃饭了");

echo "<br>";

$dangerinfo = new dangerinfo(new sms());
$dangerinfo->send("小刚","失火了，快回家");




优点
分离接口及其实现部分, 将Abstraction与Implementor分享有助于降低对实现部分编译时刻的依赖性, 接口与实现分享有助于分层，从而产生更好的结构化系统
提高可扩充性
实现细节对客户透明。