[OOP Fundamentals] Looking At Polymorphism In-Depth

00-Content.php

<?php
class Content {

   protected $title;

   protected $content;

   protected $metadata;

   public function __construct()
   {
     $this->title = "Hello World!";
     $this->content = "This is a sample piece of content.";
     $this->metadata = "<This is the metadata of the post.>";
   }

   public function getTitle()
   {
     return $this->title;
   }

   public function getContent()
   {
     return $this->content;
   }

   public function getMetadata()
   {
     return $this->metadata;
   }
 }

01-Post.php

<?php

class Post extends Content  {

   private $author;

   public function __construct() {
     parent::__construct();
     $this->author = "Tom McFarlin";
   }

   public function getAuthor()
   {
     return $this->author;
   }
 }

02-Page.php

<?php

class Page extends Content  {

   private $category;

   public function __construct() {
     parent::__construct();
     $this->category = "Articles";
   }

   public function getCategory()
   {
     return $this->category;
   }
 }

03-Run-Content.php

<?php

$content = new Content();
echo $content->getTitle();

04-Run-Post.php

<?php

// These will work because they reside in the Content base class.
$post = new Post();
echo $post->getAuthor();
echo $post->getTitle();

05-Run-Content-As-Post.php

<?php

// This will throw an error because the method doesn't reside on Content.
$content->getAuthor();