What s the current best practice to expose deferreds primari kotlinlang #coroutines

What’s the current best practice to expose deferreds (primarily) and suspendable functions to Java APIs. I’d prefer to not require a separate API like RxJava, but as far as I can tell reactivestreams doesn’t have a Single type, and the CompleteableFuture integration doesn’t support lazy coroutines.

And specifically regarding the CompletableFutures, pretty sure there’s a pretty bad problem with Deferreds that have a

start = CoroutineStart.LAZY

val deferred = scope.async(start = CoroutineStart.LAZY) { "hello" }
val future = deferred.asCompletableFuture()

future.get() // Not sure this will actually cause the deferred to be evaluated

Esau Betancourt

04/03/2020, 5:15 PM

For a project i just used when having to handle with

CompletableFuture

future{
 
}.await(()

octylFractal

04/03/2020, 6:13 PM

I presume the reason that

asCompletableFuture()

doesn't work with LAZY is the same reason that the

scope.future

call says:

* A value of [CoroutineStart.LAZY] is not supported
 * (since `CompletableFuture` framework does not provide the corresponding capability) and
 * produces [IllegalArgumentException].

I don't know if it would be as good if

asCompletableFuture()

just failed, since you could still manually

start()

the deferred in kotlin... but maybe it deserves some documentation

Sam Garfinkel

04/03/2020, 6:15 PM

My solution was to wrap the CompletableFuture in a lazy:

val foo by lazy { scope.future { something.await() } }

I think that gets the correct behavior

In that the future will eagerly start the coroutine, but only when it’s needed

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