public function asHex()
    {
        $normalizer = function ($val) {
            return str_pad(strtoupper(dechex($val)), 2, '0', STR_PAD_LEFT);
        };

        $out = unpack('C*', $this->guid);
        $out = array_map($normalizer, $out);
        $out = implode('', $out);

        return $out;
    }