On Mon, Nov 25, 2019 at 8:52 AM Antoine Pitrou <anto...@python.org> wrote: > > > Hello, > > The spec has the following language about union type ids: > """ > Types buffer: A buffer of 8-bit signed integers. Each type in the union > has a corresponding type id whose values are found in this buffer. A > union with more than 127 possible types can be modeled as a union of unions. > """ > https://arrow.apache.org/docs/format/Columnar.html#union-layout > > However, in several places the C++ code assumes type ids are unsigned. > Java doesn't seem to implement type ids (and there is no integration > task for union types). > > In the flatbuffers description, the type ids array is modeled as an > array of signed 32-bit integers. > > Moreover, according to the language above, type ids should be restricted > to the [0, 127] interval? Which one should it be?
The (optional) type ids in the metadata provide a correspondence between the union types / children and the values found in the types buffer (data). As stated in the spec, the types buffer are 8-bit signed integers. As I recall the reason that we used [ Int ] in the metadata was that the Int type is thought to be easier for languages to work with in general when serializing/deserializing the metadata. Functionally these values are limited to the range [0, 127] and so we should probably add some comments about this in Schema.fbs > Regards > > Antoine.
