prependLazy

Prepends the given source to the flow, consuming it until completion before the original source is consumed.

Fan-in operators

Signature

Source.prependSource.prepend Flow.prependFlow.prepend

Description

Prepends the given source to the flow, consuming it until completion before the original source is consumed.

Both streams will be materialized together, however, the original stream will be pulled for the first time only after the prepended upstream was completed. (In contrast, @ref(prepend)[prepend.md], introduces single-element buffers after both, original and given sources so that the original source is also pulled once immediately.)

If materialized values needs to be collected prependLazyMat is available.

See also prepend which is detached.

Example

Scala

copysourceval ladies = Source(List("Emma", "Emily"))
val gentlemen = Source(List("Liam", "William"))

gentlemen.prependLazy(ladies).runWith(Sink.foreach(println))
// this will print "Emma", "Emily", "Liam", "William"

Java

copysourceimport org.apache.pekko.stream.javadsl.Keep;
import org.apache.pekko.stream.javadsl.Source;
import org.apache.pekko.stream.javadsl.Sink;

import java.util.*;

Reactive Streams semantics