To ensure compatibility with stored string data, we need to make sure that the format of a guid string remains the same. Most guid strings are in the form XXXX-XXXX-XXXX-XXXX-XXXX, but our format doesn't separate the blocks. Equally important, we need to test string_to_guid. On the other hand, the hash tables aren't persisted, so as long as guid_hash_to_guint produces an unsigned int, it's good.