refactor(posts): make explicit the cancelling is only handled with th…

…rowing an exception

blog-ws-commons/src/main/scala/io/github/tassiLuca/dse/blog/core/PostsModel.scala

@@ -1,6 +1,7 @@
 package io.github.tassiLuca.dse.blog.core
 
 import java.util.Date
+import scala.util.Try
 
 /** The model of a simple blog posts service. */
 trait PostsModel:
@@ -23,12 +24,12 @@ trait PostsModel:
   /** A blog post, comprising an author, title, body and the last modification. */
   case class Post(author: Author, title: Title, body: Body, lastModification: Date)
 
-  /** A function that verifies the content of the post, returning [[Right]] with the content of
-    * the post if the verification succeeds or [[Left]] with the reason why failed.
+  /** A function that verifies the content of the post, returning a [[scala.util.Success]] with
+    * the content of  the post if the verification succeeds or a [[scala.util.Failure]] otherwise.
     */
-  type ContentVerifier = (Title, Body) => Either[String, PostContent]
+  type ContentVerifier = (Title, Body) => Try[PostContent]
 
-  /** A function that verifies the author has appropriate permissions, returning [[Right]]
-    * with their information or [[Left]] with the reason why failed.
+  /** A function that verifies the author has appropriate permissions, returning a
+    * [[scala.util.Success]] with their information or a [[scala.util.Failure]] otherwise.
     */
-  type AuthorsVerifier = AuthorId => Either[String, Author]
+  type AuthorsVerifier = AuthorId => Try[Author]

blog-ws-direct/src/main/scala/io/github/tassiLuca/dse/blog/PostsServiceComponent.scala

@@ -47,14 +47,14 @@ trait PostsServiceComponent:
         context.repository.save(Post(author, post._1, post._2, Date()))
 
       /* Pretending to make a call to the Authorship Service that keeps track of authorized authors. */
-      private def authorBy(id: AuthorId)(using Async, CanFail): Author =
+      private def authorBy(id: AuthorId)(using Async): Author =
         "PostsService".simulates(s"getting author $id info...", maxDuration = 1_000)
-        authorsVerifier(id).?
+        authorsVerifier(id).get
 
       /* Some local computation that verifies the content of the post is appropriate. */
-      private def verifyContent(title: Title, body: Body)(using Async, CanFail): PostContent =
+      private def verifyContent(title: Title, body: Body)(using Async): PostContent =
         "PostsService".simulates(s"verifying content of post '$title'", minDuration = 1_000)
-        contentVerifier(title, body).?
+        contentVerifier(title, body).get
 
       override def get(title: Title)(using Async, CanFail): Option[Post] =
         context.repository.load(title)

blog-ws-direct/src/test/scala/io/github/tassiLuca/dse/blog/BlogPostsServiceTest.scala

@@ -8,6 +8,8 @@ import org.scalatest.BeforeAndAfterEach
 import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers.shouldBe
 
+import scala.util.Success
+
 class BlogPostsServiceTest extends AnyFlatSpec with BeforeAndAfterEach:
 
   val authorId = "mrossi"
@@ -63,9 +65,9 @@ class BlogPostsServiceTest extends AnyFlatSpec with BeforeAndAfterEach:
     override def completedChecks: Set[Check] = _completedChecks
     override val contentVerifier: ContentVerifier = (t, b) =>
       _completedChecks += Check.ContentVerified
-      Right((t, b))
+      Success((t, b))
     override val authorsVerifier: AuthorsVerifier = a =>
       require(a == authorId, "No author with the given id matches")
       _completedChecks += Check.AuthorVerified
-      Right(Author(a, "Mario", "Rossi"))
+      Success(Author(a, "Mario", "Rossi"))
     override val service: PostsService = PostsService(contentVerifier, authorsVerifier)

blog-ws-monadic/src/main/scala/io/github/tassiLuca/dse/blog/PostsServiceComponent.scala

@@ -53,12 +53,12 @@ trait PostsServiceComponent:
       /* Pretending to make a call to the Authorship Service that keeps track of authorized authors. */
       private def authorBy(id: AuthorId)(using ExecutionContext): Future[Author] = Future:
         "PostsService".simulatesBlocking(s"getting author $id info...", maxDuration = 1_000)
-        authorsVerifier(id) match { case Left(e) => throw RuntimeException(e); case Right(v) => v }
+        authorsVerifier(id).get
 
       /* Some local computation that verifies the content of the post is appropriate. */
       private def verifyContent(title: Title, body: Body)(using ExecutionContext): Future[PostContent] = Future:
         "PostsService".simulatesBlocking(s"verifying content of the post '$title'", minDuration = 1_000)
-        contentVerifier(title, body) match { case Left(e) => throw RuntimeException(e); case Right(v) => v }
+        contentVerifier(title, body).get
 
       override def get(title: Title)(using ExecutionContext): Future[Option[Post]] =
         context.repository.load(title)

blog-ws-monadic/src/test/scala/io/github/tassiLuca/dse/blog/BlogPostsServiceTest.scala

@@ -7,6 +7,7 @@ import org.scalatest.matchers.should.Matchers.shouldBe
 
 import scala.concurrent.duration.{DurationInt, FiniteDuration}
 import scala.concurrent.{Await, ExecutionContext}
+import scala.util.Success
 
 class BlogPostsServiceTest extends AnyFlatSpec with BeforeAndAfterEach:
 
@@ -15,18 +16,6 @@ class BlogPostsServiceTest extends AnyFlatSpec with BeforeAndAfterEach:
   val postTitle = "A hello world post"
   val postBody = "Hello World Scala Gears!"
 
-  def newBlogPostsAppInstance(): BlogPostsApp & CheckFlag = new BlogPostsApp with CheckFlag:
-    private var _completedChecks: Set[Check] = Set.empty
-    override def completedChecks: Set[Check] = _completedChecks
-    override val contentVerifier: ContentVerifier = (t, b) =>
-      _completedChecks += Check.ContentVerified
-      Right((t, b))
-    override val authorsVerifier: AuthorsVerifier = a =>
-      require(a == authorId, "No author with the given id matches")
-      _completedChecks += Check.AuthorVerified
-      Right(Author(a, "Mario", "Rossi"))
-    override val service: PostsService = PostsService(contentVerifier, authorsVerifier)
-
   given ExecutionContext = ExecutionContext.global
 
   "BlogPostsService" should "create posts correctly if author and content is legit" in {
@@ -66,3 +55,15 @@ class BlogPostsServiceTest extends AnyFlatSpec with BeforeAndAfterEach:
     Thread.sleep(3_000) // waiting for the max duration of the content verification check
     app.completedChecks shouldBe Set(Check.ContentVerified)
   }
+
+  def newBlogPostsAppInstance(): BlogPostsApp & CheckFlag = new BlogPostsApp with CheckFlag:
+    private var _completedChecks: Set[Check] = Set.empty
+    override def completedChecks: Set[Check] = _completedChecks
+    override val contentVerifier: ContentVerifier = (t, b) =>
+      _completedChecks += Check.ContentVerified
+      Success((t, b))
+    override val authorsVerifier: AuthorsVerifier = a =>
+      require(a == authorId, "No author with the given id matches")
+      _completedChecks += Check.AuthorVerified
+      Success(Author(a, "Mario", "Rossi"))
+    override val service: PostsService = PostsService(contentVerifier, authorsVerifier)

docs/presentation/direct-style-presentation.tex

@@ -245,6 +245,7 @@ \section{Scala \texttt{gears}}
   \small
   \lstinputlisting[language=scala]{listings/example-1/PostsServiceImpl.scala}
   \texttt{zip} operator allows combining the results of two \texttt{Future}s in a pair if both succeed, or fail with the first error encountered. Combined with \texttt{Async.group} the failure of one determines the cancellation of the other.
+  Note: the only way \texttt{authorBy} and \texttt{verifyContent} can fail, making the \texttt{zip} return immediately the failure (thus cancelling the other check) is by throwing an exception!
 \end{frame}
 %
 \begin{frame}{Sources operators}