Operator docs for Source.tick (#28225)

akka-docs/src/test/scala/docs/stream/operators/source/Tick.scala

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2009-2019 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.source
+
+import akka.NotUsed
+import akka.actor.Cancellable
+import akka.actor.typed.ActorRef
+import akka.actor.typed.ActorSystem
+import akka.stream.scaladsl.Source
+import akka.actor.typed.scaladsl.AskPattern._
+import akka.stream.scaladsl.Flow
+import akka.util.Timeout
+
+import scala.concurrent.Future
+import scala.concurrent.duration._
+
+object Tick {
+  // not really a runnable example, these are just pretend
+  implicit val system: ActorSystem[Nothing] = null
+  val myActor: ActorRef[MyActor.Command] = null;
+
+  object MyActor {
+    sealed trait Command {}
+    case class Query(replyTo: ActorRef[Response]) extends Command
+    case class Response(text: String)
+  }
+
+  def simple() {
+    // #simple
+    Source
+      .tick(
+        1.second, // delay of first tick
+        1.second, // delay of subsequent ticks
+        "tick" // element emitted each tick
+      )
+      .runForeach(println)
+    // #simple
+  }
+
+  def pollSomething() {
+    // #poll-actor
+    val periodicActorResponse: Source[String, Cancellable] = Source
+      .tick(1.second, 1.second, "tick")
+      .mapAsync(1) { _ =>
+        implicit val timeout: Timeout = 3.seconds
+        val response: Future[MyActor.Response] = myActor.ask(MyActor.Query)
+        response
+      }
+      .map(_.text);
+    // #poll-actor
+
+    // #zip-latest
+    val zipWithLatestResponse: Flow[Int, (Int, String), NotUsed] =
+      Flow[Int].zipLatest(periodicActorResponse);
+    // #zip-latest
+  }
+}