Why are outputted protos not classes

[Ekrekr]

I'm trying out migrating to this from a different proto library because in general this looks much better! However we have hit a bit of a roadblock. We have variables that are of types of multiple kinds of protos. For example, we have a function that looks like:

function(a: proto1 | proto2 | proto3) {
  if (a instanceof proto1) {
    ...
  }
}

Because ts-proto generates an output of:

interface proto1 {...}
const proto1 = {...}
...

rather than classes, there doesn't seem to be a way of validating the proto type in this scenario - instanceof doesn't work with interfaces. Is there an expected way of accomplishing this?

See https://github.com/dataform-co/dataform/pull/1462/files#diff-8ac9e2a1b048a5e2289c9d7b9fcf1955150ce19191b86fc76c0e6cd7a643148a for full WIP.

[stephenh]

Avoiding classes was just one of the original "idiomatic TS / just POJOs" design goals for ts-proto, and I think that has generally worked out + is what most users prefer / like about the library.

It is not instanceof, but there is an option to add a $type field to every message that would let you do similar checks but more like ADTs instead of classes:

--ts_proto_opt=outputTypeRegistry=true

I kinda thought we had an option to output $type but not literally the whole type registry infra...but maybe not.

[Ekrekr]

Thanks, this is what I was looking for!

Not outputting the whole type registry infra would be super useful - getting it to play nicely with Bazel at the moment is difficult.

[stephenh]

Good! Fwiw I think adding a outputTypeFlag or something that did "just $type" from the type registry code would be a pretty simple PR; if you wanted to take a crack at it, that'd be great. Thanks!