Docs: mergeLatest (#28586)

akka-docs/src/main/paradox/stream/operators/Source-or-Flow/mergeLatest.md

@@ -4,20 +4,30 @@ Merge multiple sources.
 
 @ref[Fan-in operators](../index.md#fan-in-operators)
 
-@@@div { .group-scala }
-
 ## Signature
 
-@@signature [Flow.scala](/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala) { #mergeLatest }
+@apidoc[Flow.mergeLatest](Flow) { scala="#mergeLatest[U%3E:Out,M](that:akka.stream.Graph[akka.stream.SourceShape[U],M],eagerComplete:Boolean):FlowOps.this.Repr[scala.collection.immutable.Seq[U]]" java="#mergeLatest(akka.stream.Graph,boolean)" } 
-
-@@@
 
 ## Description
 
 MergeLatest joins elements from N input streams into stream of lists of size N.
-i-th element in list is the latest emitted element from i-th input stream.
+The i-th element in list is the latest emitted element from i-th input stream.
 MergeLatest emits list for each element emitted from some input stream,
 but only after each input stream emitted at least one element
+If `eagerComplete` is set to true then it completes as soon as the first upstream
+completes otherwise when all upstreams complete.
+
+## Example
+
+This example takes a stream of prices and quantities and emits the price each time the
+price of quantity changes:
+
+Scala
+:   @@snip [MergeLatest.scala](/akka-docs/src/test/scala/docs/stream/operators/sourceorflow/MergeLatest.scala) { #mergeLatest }
+ 
+Java
+:   @@snip [MergeLatest.java](/akka-docs/src/test/java/jdocs/stream/operators/sourceorflow/MergeLatest.java) { #mergeLatest }
+ 
 
 ## Reactive Streams semantics
 

akka-docs/src/test/java/jdocs/stream/operators/sourceorflow/MergeLatest.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package jdocs.stream.operators.sourceorflow;
+
+import akka.NotUsed;
+import akka.actor.typed.ActorSystem;
+import akka.stream.javadsl.Source;
+
+import java.util.Arrays;
+
+public class MergeLatest {
+
+  private static final ActorSystem<Void> system = null;
+
+  public static void example() {
+    // #mergeLatest
+    Source<Integer, NotUsed> prices = Source.from(Arrays.asList(100, 101, 99, 103));
+    Source<Integer, NotUsed> quantities = Source.from(Arrays.asList(1, 3, 4, 2));
+
+    prices
+        .mergeLatest(quantities, true)
+        .map(priceAndQuantity -> priceAndQuantity.get(0) * priceAndQuantity.get(1))
+        .runForeach(System.out::println, system);
+
+    // prints something like:
+    // 100
+    // 101
+    // 303
+    // 297
+    // 396
+    // 412
+    // 206
+    // #mergeLatest
+  }
+}

akka-docs/src/test/scala/docs/stream/operators/sourceorflow/MergeLatest.scala

@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.sourceorflow
+import akka.actor.ActorSystem
+import akka.stream.scaladsl.Source
+
+object MergeLatest extends App {
+  implicit val system = ActorSystem()
+
+  //#mergeLatest
+  val prices = Source(List(100, 101, 99, 103))
+  val quantity = Source(List(1, 3, 4, 2))
+
+  prices
+    .mergeLatest(quantity)
+    .map {
+      case price :: quantity :: Nil => price * quantity
+    }
+    .runForeach(println)
+
+  // prints something like:
+  // 100
+  // 101
+  // 303
+  // 297
+  // 396
+  // 412
+  // 206
+  //#mergeLatest
+}