Yes, you’re right. It’s true of any record. It’s rare I end up with no required field for a record. The idea of a metadata container - such as a custom “extension” record to a base record - does sound like a meaningful use case.
On Sat, Dec 14, 2019 at 3:50 AM roger peppe <rogpe...@gmail.com> wrote: > On Sat, 14 Dec 2019 at 04:58, Vance Duncan <dunca...@gmail.com> wrote: > >> Because you will forever be limited to adding nullable fields to that >> record. It will forever be a weak contract. That may be OK, depending on >> the situation. You just won’t be able to enforce semantics through the >> schema. The code will have to enforce all constraints. >> > > As I understand it, that's true when adding fields to *any* record over > time, whether the record starts off with ten fields or none. > > As you say, it may be OK in some situations, so ISTM that it shouldn't be > forbidden by the specification. > > One possible concrete use case for an empty record is to reserve a field > in a record for future extensible use; for metadata, for example. > This could be somewhat nicer than using a map type because you get the > capability to add specific fields. > Perhaps the OCF format could have done something like this for the file > metadata field. > > cheers, > rog. > > >> On Fri, Dec 13, 2019 at 6:28 PM roger peppe <rogpe...@gmail.com> wrote: >> >>> >>> >>> On Fri, 13 Dec 2019 at 23:08, Vance Duncan <dunca...@gmail.com> wrote: >>> >>>> Sorry about that. I was assuming some kind of name-based schema >>>> registry lookup. Assume you are looking up schemas by name using a schema >>>> registry. Let’s say the record is name MyRecord. You subsequently add a >>>> required field to it. Since the new record is not reverse compatible, >>>> you’ll need to name it MyRecord2, or whatever. This is what I meant by >>>> “reidentify”. >>>> >>> >>> I don't quite get how this is different to having a struct with any >>> other number of fields. Why should zero be special here? >>> >>> >>>> On Fri, Dec 13, 2019 at 12:46 PM roger peppe <rogpe...@gmail.com> >>>> wrote: >>>> >>>>> >>>>> >>>>> On Fri, 13 Dec 2019 at 15:02, Vance Duncan <dunca...@gmail.com> wrote: >>>>> >>>>>> My immediate thought is observe the YAGNI principle and only create >>>>>> it if and when you need it. Otherwise, you run the risk of requiring >>>>>> non-interchangeable re-identification if you need required, non-default, >>>>>> fields when the need materializes. >>>>>> >>>>> >>>>> Could you expand a little on that latter point, please? I'm not sure I >>>>> understand what you're saying. >>>>> A concrete example might help. >>>>> >>>>> cheers, >>>>> rog. >>>>> >>>>>> >>>>>> >>>>>> On December 13, 2019, at 9:25 AM, roger peppe <rogpe...@gmail.com> >>>>>> wrote: >>>>>> >>>>>> >>>>>> Hi, >>>>>> >>>>>> The specification doesn't seem to make it entirely clear whether it's >>>>>> allowable for a record to contain no fields (a zero-length array for the >>>>>> fields member). I've found at least one implementation that complains >>>>>> about >>>>>> a record with an empty fields array, and I'm wondering if this is a bug. >>>>>> >>>>>> A record containing no fields is actually quite useful as it can act >>>>>> as a placeholder for a record with any number of extra fields in future >>>>>> evolutions of a schema. >>>>>> >>>>>> What do you think? >>>>>> >>>>>> cheers, >>>>>> rog. >>>>>> >>>>> -- >>>> Regards, >>>> >>>> Vance Duncan >>>> mailto:dunca...@gmail.com >>>> http://www.linkedin.com/in/VanceDuncan >>>> (904) 553-5582 >>>> >>> -- >> Regards, >> >> Vance Duncan >> mailto:dunca...@gmail.com >> http://www.linkedin.com/in/VanceDuncan >> (904) 553-5582 >> > -- Regards, Vance Duncan mailto:dunca...@gmail.com http://www.linkedin.com/in/VanceDuncan (904) 553-5582
