Source.unfold examples (#28081)

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

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2009-2019 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.source
+
+import akka.NotUsed
+import akka.stream.scaladsl.Source
+
+object Unfold {
+
+  // #countdown
+  def countDown(from: Int): Source[Int, NotUsed] =
+    Source.unfold(from) { current =>
+      if (current == 0) None
+      else Some((current - 1, current))
+    }
+  // #countdown
+
+  // #fibonacci
+  def fibonacci: Source[BigInt, NotUsed] =
+    Source.unfold((BigInt(0), BigInt(1))) {
+      case (a, b) =>
+        Some(((b, a + b), a))
+    }
+  // #fibonacci
+
+}