User::getInstance

static function getInstance($userId, $groupId = 0)
{
	if (!self::$instance ||
		!array_key_exists($userId, self::$instance) ||
		!array_key_exists($groupId, self::$instance[$userId]))
	{
		self::$instance[$userId][$groupId] = new self($userId, $groupId);
	}

	return self::$instance[$userId][$groupId];
}