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);