Hi Jeff,
your API seems quite complex. I don't know the purpose of it so I cannot
suggest anything but I'd try to simplify. :)
That said, your problem seems to be that you cannot write a concrete type
that would express the dependency between the two components of the tuple
`(RequestBuilder, Promise[???])`. There are two ways to solve it:
1) make `Out` a type parameter and convert `sink` to a `def sink[Out]`,
then you can use the tuple `(RequestBuilder[Out], Promise[Out])`
2) create your custom tuple type that allows to express the dependency:
case class BuilderWithPromise[O](builder: RequestBuilder { type Out = O },
promise: Promise[O])
and then use it as MergeHub.source[BuilderWithPromise[_]]
But I can only repeat that getting rid of the dependent types if possible
is usually the best solution ;)
Johannes
On Thursday, July 6, 2017 at 11:23:50 PM UTC+2, Jeff wrote:
>
> Here is a strawman program which illustrates the issue I am having
>
> trait RequestBuilder {
> type Out
>
> def complete(p: Promise[Out]): Unit
> }
>
> def makeRequest(in: RequestBuilder): Source[(RequestBuilder,
> Promise[in.Out]), Future[in.Out]] = {
> val p = Promise[in.Out]
>
> Source.single(in -> p).mapMaterializedValue(_ => p.future)
> }
>
> val sink = MergeHub.source[(RequestBuilder, Promise[???])].to(Sink.foreach {
> case (r, p) => r.complete(p)
> }).run()
>
> sink.runWith(makeRequest(new RequestBuilder {
> type Out = Int
>
> def complete(p: Promise[Out]): Unit = p.success(1)
> }))
>
>
> The issue is, how do I type the Promise[???] in the sink? I have been
> able to work around this by making the Promise a part of the RequestBuilder
> trait itself, but this seems like a code smell to me
>
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