php装饰器模式完成文章编辑

<?php 
//文章父类
class BaseArt{
   protected $content;
   protected $art;

   public function __construct($content){    
      $this->content=$content;
   }
   public function decorator(){
       return $this->content;
   }
}
//摘要
class BianArt extends BaseArt{
   public function __construct(BaseArt $art){
           $this->art=$art;
           $this->decorator();
   }
   public function decorator(){
      return  $this->content=$this->art->decorator().'文章摘要';   
   }
}
//SEO关键词
class SEOArt extends BaseArt{
   public function __construct(BaseArt $art){
           $this->art=$art;
           $this->decorator();
   }
   public function decorator(){
      return  $this->content=$this->art->decorator().'SEO优化';   
   }
}

$BA=new BaseArt('天天向上');
$b=new BianArt($BA);
echo $b->decorator();
$c=new SEOArt($b);
echo $c->decorator();