content = $content;    }        public function decorator(){        return $this->content;    }}//编辑文章摘要class BianArt extends BaseArt {    public function __construct(BaseArt $art){        $this->art = $art;    }        public function decorator(){        return $this->content = $this->art->decorator() . ',小编加上文章摘要';    }}class SEOart extends BaseArt {    public function __construct(BaseArt $art){        $this->art = $art;    }        public function decorator(){        return $this->content = $this->art->decorator() . ',SEO加上关键词';    }}$b = new SEOart(new BianArt(new BaseArt('天天向上')));echo $b->decorator();