prepend

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

Signature

def prepend[U >: Out, Mat2](that: Graph[SourceShape[U], Mat2]): Repr[U]
def prependMat[U >: Out, Mat2, Mat3](that: Graph[SourceShape[U], Mat2])(matF: (Mat, Mat2) => Mat3): ReprMat[U, Mat3]

Description

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

If materialized values needs to be collected prependMat is available.

emits when the given stream has an element available; if the given input completes, it tries the current one

backpressures when downstream backpressures

completes when all upstreams complete

Example

Scala

sourceimport akka.stream.scaladsl.Source
import akka.stream.scaladsl.Sink

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

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

Java

sourceimport akka.stream.javadsl.Source;
import akka.stream.javadsl.Sink;
import java.util.Arrays;

Source<String, NotUsed> ladies = Source.from(Arrays.asList("Emma", "Emily"));
Source<String, NotUsed> gentlemen = Source.from(Arrays.asList("Liam", "William"));
gentlemen.prepend(ladies).runWith(Sink.foreach(System.out::print), materializer);
// this will print "Emma", "Emily", "Liam", "William"