Wouldn't support for ADT require expressing more than 1 type id per record? In other words, if `put` has type id 1, `delete` has type id 2, and `erase` has type id 3 then there is no way to express something is (for example) both type id 1 and type id 3 because you can only have one type id per record.
If that understanding is correct then it seems you can always encode world 2 into world 1 by exhaustively listing out the combinations. In other words, `put` is the LSB, `delete` is bit 2, and `erase` is bit 3 and you have: 7 - put/delete/erase 6 - delete/erase 5 - erase/put 4 - erase 3 - put/delete 2 - delete 1 - put On Tue, Apr 2, 2024 at 4:36 AM Finn Völkel <f...@juxt.pro> wrote: > I also meant Algebraic Data Type not Abstract Data Type (too many > acronymns). > > On Tue, 2 Apr 2024 at 13:28, Antoine Pitrou <anto...@python.org> wrote: > > > > > Thanks. The Arrow spec does support multiple union members with the same > > type, but not all implementations do. The C++ implementation should > > support it, though to my surprise we do not seem to have any tests for > it. > > > > If the Java implementation doesn't, then you can probably open an issue > > for it (and even submit a PR if you would like to tackle it). > > > > I've also opened https://github.com/apache/arrow/issues/40947 to create > > integration tests for this. > > > > Regards > > > > Antoine. > > > > > > Le 02/04/2024 à 13:19, Finn Völkel a écrit : > > >> Can you explain what ADT means ? > > > > > > Sorry about that. ADT stands for Abstract Data Type. What do I mean by > an > > > ADT style vector? > > > > > > Let's take an example from the project I am on. We have an `op` union > > > vector with three child vectors `put`, `delete`, `erase`. `delete` and > > > `erase` have the same type but represent different things. > > > > > > On Tue, 2 Apr 2024 at 13:16, Steve Kim <chairm...@gmail.com> wrote: > > > > > >> Thank you for asking this question. I have the same question. > > >> > > >> I noted a similar problem in the c++/python implementation: > > >> https://github.com/apache/arrow/issues/19157#issuecomment-1528037394 > > >> > > >> On Tue, Apr 2, 2024, 04:30 Finn Völkel <f...@juxt.pro> wrote: > > >> > > >>> Hi, > > >>> > > >>> my question primarily concerns the union layout described at > > >>> https://arrow.apache.org/docs/format/Columnar.html#union-layout > > >>> > > >>> There are two ways to use unions: > > >>> > > >>> - polymorphic vectors (world 1) > > >>> - ADT style vectors (world 2) > > >>> > > >>> In world 1 you have a vector that stores different types. In the ADT > > >> world > > >>> you could have multiple child vectors with the same type but > different > > >> type > > >>> ids in the union type vector. The difference is apparent if you want > to > > >> use > > >>> two BigIntVectors as children which doesn't exist in world 1. World 1 > > is > > >> a > > >>> subset of world 2. > > >>> > > >>> The spec (to my understanding) doesn’t explicitly forbid world 2, but > > the > > >>> implementation we have been using (Java) has been making the > assumption > > >> of > > >>> being in world 1 (a union only having ONE child of each type). We > > >> sometimes > > >>> use union in the ADT style which has led to problems down the road. > > >>> > > >>> Could someone clarify what the specification allows and what it > doesn’t > > >>> allow? Could we tighten the specification after that clarification? > > >>> > > >>> Best, Finn > > >>> > > >> > > > > > >
