<?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();