CODEWITHSUNDEEP
scalaakkaakka-stream
Khanetor
Khanetor

Reputation: 12302

When not to use NotUsed in Akka Stream

I have seen a lot of Akka stream examples that use NotUsed, but I have not been able to find one where something other than NotUsed was used. I tried creating a source that does not have NotUsed, but it does not seem to be passed to the next flow. I would appreciate if someone can explain when and how we want to have something other than NotUsed.

Upvotes: 1

Views: 267

Answers (1)

artur
artur

Reputation: 1760

This part of Akka Streams documentation details the "materialized value" and how they compose (so that you can pass what you need to the next flow): https://doc.akka.io/docs/akka/current/stream/stream-composition.html#materialized-values

Also other parts of the documentation also use not-NotUsed values.

Like in the first snippet here

val source = Source(1 to 10)
val sink = Sink.fold[Int, Int](0)(_ + _)

// connect the Source to the Sink, obtaining a RunnableGraph
val runnable: RunnableGraph[Future[Int]] = source.toMat(sink)(Keep.right)

// materialize the flow and get the value of the sink
val sum: Future[Int] = runnable.run()

Upvotes: 3

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