Aw: [akka-user] Akka 2.5.11 - materialization of Flow.lazyInit

Stefan Wachter Mon, 05 Mar 2018 04:32:52 -0800

I just saw that Source.lazily implements a similar concept:

def lazily[T, M](create: () ⇒ Source[T , M]): Source[T, Future[M]]

Here a the materialized value is a Future that is failed if there was no demand before the source gets never created.

I think the two methods Source.lazily and Flow.lazyInit should be alligned (in their name and in their materialized values)

Gesendet: Montag, 05. März 2018 um 13:13 Uhr
Von: "Stefan Wachter" <stefan.wach...@gmx.de>
An: akka-user@googlegroups.com
Betreff: [akka-user] Akka 2.5.11 - materialization of Flow.lazyInit

Hi,

studying the newly Flow constructor Flow.lazyInit

def lazyInit[I, O, M](flowFactory: I ⇒ Future[Flow[I, O, M]], fallback: () ⇒ M): Flow[I, O, M]

(cf. https://doc.akka.io/api/akka/2.5.11/akka/stream/scaladsl/Flow$.html) I wondered how (citation from ScalaDoc)

The materialized value of the `Flow` will be the materialized
value of the created internal flow.

could be? Materialization happens before the flow is run. Therefore the materialized value cannot depend on whether their will be some input or not.

To fix the issue, the materialzed value of Flow.lazyInit should be a Future[M] or even better a Future[Option[M]]. In case that no internal flow is materialized it would be a Future[None].

--Stefan

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Aw: [akka-user] Akka 2.5.11 - materialization of Flow.lazyInit

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