Inheritable PHP Singleton

gistfile1.php

<?php
	class Object{
		//...
		private static $singletons	= array();
		public static function &singleton(){
			$class = get_called_class();
			if(!array_key_exists($class, self::$singletons)){
				self::$singletons[$class] = new $class();
			}
			return self::$singletons[$class];
		}
		//...
	}