Question

For my project I’ve wrote a basic controller class:

<?php
   abstract class Controller
   {
      static $__instance = null;

      protected function __construct()
      {
      }

      final private function __clone()
      {
      }

      public static function getInstance()
      {
         $class = get_called_class();

         return self::$__instance ? self::$__instance : (self::$__instance = new $class());
      }
   }
?>

Now every controller does inheritance from this controller.

Like this:

<?php

   include_once 'model/page.php';
   include_once 'view/page.php';

   class PageController extends Controller
   {
      private $m_model = null;

      private $m_view = null;

      private $m_id;

      protected function __construct()
      {
         parent::__construct();

         $this->m_id = uniqid();

         $this->m_model = new PageModel();
         $this->m_view = new PageView();
      }

      public function preparePage()
      {
         echo 'Hello';
      }
   }
?>

And in my index.php I got this:
$user = UserController::getInstance();
$page = PageController::getInstance();
var_dump($page);

The problem is that the var_dump($page) shows that the variable $page is type of UserController, but why? It should be of the type PageController. Any ideas?

Answer 1

Because there’s only one self::$__instance which is shared among all classes that inherit from Controller. You can use an array to keep track of multiple instances:

return self::$__instance[$class] ? self::$__instance[$class] : (self::$__instance[$class] = new $class());

But really, singleton patterns are frowned upon. You should instantiate new PageController once at a defined location and inject it down where it is needed. Then there’s no need for this static singleton constructor.