Pack Union

1 Version

Merges N independently-typed input streams t1, t2, ... into a single union t1|t2, tagging each emitted value with the variant of the input it came from. Inputs are alternatives, not co-arriving fields. Inverse of unpack_union.

How it fits

Typical backends

Build a tagged-sum event channel from two unrelated sources and ship it as JSON for a consumer to route by variant.

Multiplex a fault channel and a normal payload channel, then split them back apart on the consumer side.

Caveats

I/O contractExactly one variant is emitted per tick, corresponding to whichever input fired; unlike pack_tuple / pack_record the inputs are alternatives, not co-arriving fields.
Hard constraintInputs must not fire simultaneously on a single tick; concurrent fires resolve non-deterministically.
I/O contractDownstream must unpack_union or type-branch before reading variant-specific fields.
Hard constraintThe variant tag is positional; reordering inputs changes which value gets which tag and is a breaking change.

Versions

25fe570ddefaultlatestTransformation
8/19/2022