public static function cached_object($obj, $class = null)
	{
		$class = $class ?: get_called_class();
		$id    = (is_int($obj) or is_string($obj)) ? (string) $obj : $class::implode_pk($obj);

		$result = ( ! empty(static::$_cached_objects[$class][$id])) ? static::$_cached_objects[$class][$id] : false;

		return $result;
	}