Use the “Ask Pattern” to send each stream element (without the context) as an ask to the target actor (of the new actors API), and expect a reply that will be emitted downstream.

Actor interop operators


This operator is included in:

val AkkaVersion = "2.9.3"
libraryDependencies += "com.typesafe.akka" %% "akka-stream-typed" % AkkaVersion
def versions = [
  ScalaBinary: "2.13"
dependencies {
  implementation platform("com.typesafe.akka:akka-bom_${versions.ScalaBinary}:2.9.3")

  implementation "com.typesafe.akka:akka-stream-typed_${versions.ScalaBinary}"




Use the Ask pattern to send a request-reply message to the target ref actor. The stream context is not sent, instead it is locally recombined to the actor’s reply.

If any of the asks times out it will fail the stream with an AskTimeoutExceptionAskTimeoutException.

The ask operator requires

  • the actor ref,
  • a makeMessage function to create the message sent to the actor from the incoming element, and the actor ref accepting the actor’s reply message
  • a timeout.

Reactive Streams semantics

emits when the futures (in submission order) created by the ask pattern internally are completed

backpressures when the number of futures reaches the configured parallelism and the downstream backpressures

completes when upstream completes and all futures have been completed and all elements have been emitted

fails when the passed-in actor terminates, or when any of the asks exceed a timeout

cancels when downstream cancels

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