Merge pull request #518 from mdipirro/scala-463

Scala 463 - Add code for the scala-async article

Author: dominiqueplante

build.sbt

@@ -299,7 +299,13 @@ lazy val scala_libraries_4 = (project in file("scala-libraries-4"))
   .settings(
     name := "scala-libraries-4",
     libraryDependencies += "com.lihaoyi" %% "utest" % "0.8.1" % "test",
-    testFrameworks += new TestFramework("utest.runner.Framework")
+    testFrameworks += new TestFramework("utest.runner.Framework"),
+    libraryDependencies += "org.scalatest" %% "scalatest" % "3.1.2" % Test,
+    libraryDependencies ++= Seq(
+      "org.scala-lang.modules" %% "scala-async" % "1.0.1",
+      "org.scala-lang" % "scala-reflect" % scalaVersion.value % Provided
+    ),
+    scalacOptions += "-Xasync"
   )
 
 lazy val scala_strings = (project in file("scala-strings"))

scala-libraries-4/src/test/scala/com/baeldung/scala/async/ScalaAsyncTest.scala

@@ -0,0 +1,88 @@
+package com.baeldung.scala.async
+
+import org.scalatest.concurrent.ScalaFutures
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.time.{Millis, Seconds, Span}
+import org.scalatest.wordspec.AnyWordSpec
+
+import scala.async.Async.{async, await}
+import scala.concurrent.Future
+
+object ScalaAsyncTest {
+  import scala.concurrent.ExecutionContext.Implicits.global
+
+  def slowComputation: Future[Int] = Future {
+    Thread.sleep(1000)
+    10
+  }
+
+  def anotherSlowComputation(s: String): Future[Int] = Future {
+    Thread.sleep(1500)
+    s.length
+  }
+
+  def sequentialCombination: Future[Int] = async {
+    await(slowComputation) + await(anotherSlowComputation("Baeldung"))
+  }
+
+  def parallelCombination: Future[Int] = async {
+    val r1 = slowComputation
+    val r2 = anotherSlowComputation("Baeldung")
+    await(r1) + await(r2)
+  }
+
+  /* Uncommenting this snippet will produce the following error:
+  await must not be used under a nested method. await(slowComputation)
+
+  def invalid = async {
+    def localFunction = {
+      await(slowComputation)
+    }
+
+    localFunction
+  }*/
+
+  /* Uncommenting this snippet will produce the following error:
+  await must not be used under a try/catch. await(slowComputation)
+
+  def tryCatch = async {
+    try {
+      await(slowComputation)
+    } catch {
+      case e: Throwable => println(e.getMessage)
+    }
+  }*/
+
+  def withFor: Future[Int] = for {
+    r1 <- slowComputation
+    r2 <- anotherSlowComputation("Baeldung")
+  } yield r1 + r2
+}
+
+class ScalaAsyncTest extends AnyWordSpec with Matchers with ScalaFutures {
+
+  import ScalaAsyncTest._
+
+  implicit private val defaultPatience: PatienceConfig =
+    PatienceConfig(timeout = Span(3, Seconds), interval = Span(500, Millis))
+
+  "Futures combination" should {
+    "work sequentially" in {
+      whenReady(sequentialCombination) { r =>
+        assert(r == 18)
+      }
+    }
+
+    "work in parallel" in {
+      whenReady(parallelCombination) { r =>
+        assert(r == 18)
+      }
+    }
+
+    "give the same result as Futures composed with for comprehension" in {
+      whenReady(withFor) { r =>
+        assert(r == 18)
+      }
+    }
+  }
+}