/**
* Generates an RFC 4122-compliant version 4 UUID.
*
* @return string The string representation of an RFC 4122-compliant, version 4 UUID.
* @link http://www.ietf.org/rfc/rfc4122.txt RFC 4122: UUID URN Namespace
*/
public static function generate()
{
$uuid = Random::GenerateBytes(16);
$uuid[6] = chr(ord($uuid[6]) & static::UUID_CLEAR_VER | static::UUID_VERSION_4);
$uuid[8] = chr(ord($uuid[8]) & static::UUID_CLEAR_VAR | static::UUID_VAR_RFC);
return join('-', array(bin2hex(substr($uuid, 0, 4)), bin2hex(substr($uuid, 4, 2)), bin2hex(substr($uuid, 6, 2)), bin2hex(substr($uuid, 8, 2)), bin2hex(substr($uuid, 10, 6))));
}