Question

I want to use a Registry to store some objects. Here is a simple Registry class implementation.

<?php
  final class Registry
  {
    private $_registry;
    private static $_instance;

    private function __construct()
    {
      $this->_registry = array();
    }

    public function __get($key)
    {
      return
        (isset($this->_registry[$key]) == true) ?
        $this->_registry[$key] :
        null;
    }

    public function __set($key, $value)
    {
      $this->_registry[$key] = $value;
    }

    public function __isset($key)
    {
      return isset($this->_registry[$key]);
    }

    public static function getInstance()
    {
      if (self::$_instance == null) self::$_instance = new self();
      return self::$_instance;
    }
}

?>

When I try to access this class, I get “Indirect modification of overloaded property has no effect” notification.

Registry::getInstance()->foo   = array(1, 2, 3);   // Works
Registry::getInstance()->foo[] = 4;                // Does not work

What do I do wrong?

Answer 1

This behavior has been reported as a bug a couple times:

• https://bugs.php.net/bug.php?id=42030
• https://bugs.php.net/bug.php?id=41641

It is unclear to me what the result of the discussions was although it appears to have something to do with values being passed “by value” and “by reference”. A solution that I found in some similar code did something like this:

function &__get( $index )
{
   if( array_key_exists( $index, self::$_array ) )
   {
      return self::$_array[ $index ];
   }
   return;
}

function &__set( $index, $value )
{
   if( !empty($index) )
   {
      if( is_object( $value ) || is_array( $value) )
      {
         self::$_array[ $index ] =& $value;
      }
      else
      {
         self::$_array[ $index ] =& $value;
      }
   }
}

Notice how they use &__get and &__set and also when assigning the value use & $value. I think that is the way to make this work.