What’s the current best practice to expose deferre...

# coroutines

[Sam Garfinkel]

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.

[Sam Garfinkel]

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]

For a project i just used when having to handle with CompletableFuture

future{
 
}.await(()

[octylFractal]

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].

[octylFractal]

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]

My solution was to wrap the CompletableFuture in a lazy:

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

[Sam Garfinkel]

I think that gets the correct behavior

[Sam Garfinkel]

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