public function sort(callable $cb = null)
    {
        if ($cb) {
            // Custom searches can be easier on memory, but run absurdly slow
            // pre PHP7
            if (PHP_MAJOR_VERSION < 7) {
                return $this->arraySort($cb);
            }
            return $this->mergeSort($cb);
        }
        return $this->arraySort();
    }