abstract class info{

    public $msgClass = null;

    public function __construct($obj){

        $this->msgClass = $obj;

    }

    abstract function msg();

    public function send($to,$content){

        return $this->msg() . $this->msgClass->send($to,$content);

    }

}

//QQ信息

class qq_msg{

    public function send($to,$content){

        return '【QQ消息】发送给：'.$to.'，内容：'.$content;

    }

}

//邮件信息

class email_msg{

    public function send($to,$content){

        return '【Email消息】发送给：'.$to.'，内容：'.$content;

    }

}

//短信消息

class sms_msg{

    public function send($to,$content){

        return '【短信消息】发送给：'.$to.'，内容：'.$content;

    }

}

//普通消息

class common_info extends info{

    public function msg(){

        return '【普通】';

    }

}

//警告消息

class warning_info extends info{

    public function msg(){

        return '【警告】';

    }

}

//危急消息

class danger_info extends info{

    public function msg(){

        return '【危急】';

    }

}

$a = new common_info(new email_msg());

$res = $a->send('zhang san','好好学习');

var_dump($res);

$a = new warning_info(new sms_msg());

$res = $a->send('zhang san','好好学习');

var_dump($res);