From vert.x Future to SmallRye Mutiny Uni/Multi

[Stwissel]

I’m very comfortable with vert.x’s Future/Promise and fairly new to Mutiny. Looking for a guide along the lines of “When you do this with a future, do that with Uni/Multi”

I frequently have code like:

somethingFutureA()
   .compose(this::takeAmakeB)
   .compose(this::takeBmakeC)
   .onSuccess(ctx::end);

Or

List<Future<?>> allTheThings = kickoffAllThings();
Future.all(allTheThings)
  .onSuccess(result -> {…})
  .onFailure(ShitHappens::noFuture);

Methods I design often look like this

Future<SomeResult> attemptSomeResult(SomeData parameter) {
   Promise<SomeResult> outcome = Promise.promise();
   // do stuff here
   if (success) {
      promise.complete(aSomeResultObject);
   } else {
      promise.fail(errorCondition);
   }
  return Promise.future();
}

What would be the Mutiny way?

[quarkus-bot[bot]]

/cc @Ladicek (smallrye), @cescoffier (mutiny), @jmartisk (smallrye), @jponge (mutiny), @phillip-kruger (smallrye), @radcortez (smallrye)

[Stwissel]

So far my impression:

onSuccess, onFailure, onComplete -> subscribe
compose, map -> onItem
promise -> createFrom
Future.all -> Uni.join

But I’m sure there are sufficient subtleties to trip over. I’m especially curious about how to implement takeAmakeB style Uni (or learn Mutiny style)

Subscribe to a Multi looks very much like an Observable/Observer. I wonder how could multiple subscribers subscribe to a Multi, receiving the same items

[jponge]

Coming from Vert.x the main difference of a Uni vs a Future is that a Uni needs to be subscribed to before the actual action is triggered, whereas you can't control when a Vert.x future starts. You will find lots of composition operations to transform values, compose asynchronous results, handle errors, etc.

You might want to start with https://smallrye.io/smallrye-mutiny/latest/tutorials/hello-mutiny/ and look over the documentation here.

You might also look at the samples in https://github.com/smallrye/smallrye-mutiny/tree/main/workshop-examples

Hope it helps!