Operator docs for Source.combine (#28195)

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

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2009-2019 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.source
+
+import akka.actor.ActorSystem
+// #imports
+import akka.stream.scaladsl.{ Concat, Merge, Source }
+// ...
+
+// #imports
+
+object Combine {
+  implicit val system: ActorSystem = null
+
+  def merge(): Unit = {
+    // #source-combine-merge
+    val source1 = Source(1 to 3)
+    val source2 = Source(8 to 10)
+    val source3 = Source(12 to 14)
+    val combined = Source.combine(source1, source2, source3)(Merge(_))
+    combined.runForeach(println)
+    // could print (order between sources is not deterministic)
+    // 1
+    // 12
+    // 8
+    // 9
+    // 13
+    // 14
+    // 2
+    // 10
+    // 3
+    // #source-combine-merge
+  }
+
+  @throws[Exception]
+  def concat(): Unit = {
+    // #source-combine-concat
+    val source1 = Source(1 to 3)
+    val source2 = Source(8 to 10)
+    val source3 = Source(12 to 14)
+    val sources = Source.combine(source1, source2, source3)(Concat(_))
+    sources.runForeach(println)
+    // prints (order is deterministic)
+    // 1
+    // 2
+    // 3
+    // 8
+    // 9
+    // 10
+    // 12
+    // 13
+    // 14
+    // #source-combine-concat
+  }
+}