Thanks for the great suggestions - I eventually came to the "custom tuple"
solution myself and it seems to work well.
As for the issue of complexity, it's actually not as complex as it sounds.
I'm using Http().superPool() to make api requests and I wanted to avoid
having to create a separate stream for every single iteration of api
request when the only thing that changed was the Unmarshaller. Instead of
materializing multiple streams where the only thing that changed was the
Sink, I just created one stream where the Sink.foreach(...) take the
Unmarshaller function and resolves the Promise.
On Wednesday, July 12, 2017 at 5:24:07 AM UTC-7, johannes...@lightbend.com
wrote:
>
> 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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