Operator examples for statefulMapConcat #25468

akka-docs/src/test/scala/docs/stream/operators/flow/StatefulMapConcat.scala

@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2009-2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.flow
+
+import akka.actor.ActorSystem
+import akka.stream.scaladsl.Flow
+import akka.stream.scaladsl.Source
+
+class StatefulMapConcat {
+
+  implicit val system: ActorSystem = ???
+
+  def zipWithIndex(): Unit = {
+    // #zip-with-index
+    val letterAndIndex = Source("a" :: "b" :: "c" :: "d" :: Nil).statefulMapConcat { () =>
+      var counter = 0L
+
+      // we return the function that will be invoked for each element
+      { element =>
+        counter += 1
+        // we return an iterable with the single element
+        (element, counter) :: Nil
+      }
+    }
+
+    letterAndIndex.runForeach(println)
+    // prints
+    // (a,1)
+    // (b,2)
+    // (c,3)
+    // (d,4)
+    // #zip-with-index
+  }
+
+  def blacklist(): Unit = {
+    // #blacklist
+    val fruitsAndBlacklistCommands = Source(
+      "banana" :: "pear" :: "orange" :: "blacklist:banana" :: "banana" :: "pear" :: "banana" :: Nil)
+
+    val blacklistingFlow = Flow[String].statefulMapConcat { () =>
+      var blacklist = Set.empty[String]
+
+      { element =>
+        if (element.startsWith("blacklist:")) {
+          blacklist += element.drop(10)
+          Nil // no element downstream when adding a blacklisted keyword
+        } else if (blacklist(element)) {
+          Nil // no element downstream if element is blacklisted
+        } else {
+          element :: Nil
+        }
+      }
+    }
+
+    fruitsAndBlacklistCommands.via(blacklistingFlow).runForeach(println)
+    // prints
+    // banana
+    // pear
+    // orange
+    // pear
+    // #blacklist
+  }
+
+  def reactOnEnd(): Unit = {
+    // #bs-last
+    val words = Source("baboon" :: "crocodile" :: "bat" :: "flamingo" :: "hedgehog" :: "beaver" :: Nil)
+
+    val bWordsLast = Flow[String].concat(Source.single("-end-")).statefulMapConcat { () =>
+      var stashedBWords: List[String] = Nil
+
+      { element =>
+        if (element.startsWith("b")) {
+          // prepend to stash and emit no element
+          stashedBWords = element :: stashedBWords
+          Nil
+        } else if (element.equals("-end-")) {
+          // return in the stashed words in the order they got stashed
+          stashedBWords.reverse
+        } else {
+          // emit the element as is
+          element :: Nil
+        }
+      }
+    }
+
+    words.via(bWordsLast).runForeach(println)
+    // prints
+    // crocodile
+    // flamingo
+    // hedgehog
+    // baboon
+    // bat
+    // beaver
+    // #bs-last
+  }
+
+}