public static function clearDeletedInstances() {
		if( !isset(static::$instances[static::getClass()]) ) {
			return;
		}
		$instances = &static::$instances[static::getClass()];
		foreach( $instances as $id => $obj ) {
			/* @var static $obj */
			if( $obj->isDeleted() ) {
				unset($instances[$id]);
			}
		}
	}