doOnFirst

Run the given function when the first element is received.

Simple operators

Signature

Source.doOnFirstSource.doOnFirst Flow.doOnFirstFlow.doOnFirst

Description

Run the given function when the first element is received.

The doOnFirst operator adheres to the ActorAttributes.SupervisionStrategy attribute. On Supervision.Resume the failing first element is dropped and the function is not retried; on Supervision.Restart the next element is treated as the first.

Examples

Scala

copysourceimport org.apache.pekko
import pekko.NotUsed
import pekko.stream.scaladsl._

val source: Source[Int, NotUsed] = Source(1 to 10)
val mapped: Source[Int, NotUsed] = source.doOnFirst(println)

Reactive Streams semantics