Doc example of Sink.ignore, #25468 (#28753)

akka-docs/src/test/scala/docs/stream/operators/sink/Ignore.scala

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2019-2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.sink
+
+import java.util.UUID
+
+import scala.concurrent.Future
+
+import akka.NotUsed
+import akka.actor.ActorSystem
+import akka.stream.scaladsl.Sink
+import akka.stream.scaladsl.Source
+
+object Ignore {
+  implicit val system: ActorSystem = ???
+
+  def ignoreExample(): Unit = {
+    //#ignore
+    val lines: Source[String, NotUsed] = readLinesFromFile()
+    val databaseIds: Source[UUID, NotUsed] =
+      lines.mapAsync(1)(line => saveLineToDatabase(line))
+    databaseIds.mapAsync(1)(uuid => writeIdToFile(uuid)).runWith(Sink.ignore)
+    //#ignore
+  }
+
+  private def readLinesFromFile(): Source[String, NotUsed] =
+    Source.empty
+
+  private def saveLineToDatabase(line: String): Future[UUID] =
+    Future.successful(UUID.randomUUID())
+
+  private def writeIdToFile(uuid: UUID): Future[UUID] =
+    Future.successful(uuid)
+
+}