private function tupleSort($a, $b)
    {
        $aLength = count($a);
        $bLength = count($b);

        if ($aLength > $bLength) {
            $max = $aLength;
        } else {
            $max = $bLength;
        }

        for ($i = 0; $i < $max; ++$i) {
            if ($a[$i] < $b[$i]) {
                return -1;
            }

            if ($a[$i] > $b[$i]) {
                return 1;
            }
        }

        return $aLength <=> $bLength;
    }