Merge pull request #88 from paualarco/feature/optionT

juanpedromoreno · web-flow · commit c72106cb4bcd · 2020-03-26T19:18:39.000+01:00
Added OptionT exercises
diff --git a/README.md b/README.md
@@ -16,7 +16,7 @@ to get involved, or visit our [GitHub site](https://github.com/scala-exercises).
 
 ## License
 
-Copyright (C) 2015-2019 47 Degrees, LLC.
+Copyright (C) 2015-2020 47 Degrees, LLC.
 Reactive, scalable software solutions.
 http://47deg.com
 hello@47deg.com
diff --git a/project/ProjectPlugin.scala b/project/ProjectPlugin.scala
@@ -48,7 +48,7 @@ object ProjectPlugin extends AutoPlugin {
         Resolver.sonatypeRepo("releases")
       ),
       headerLicense := Some(Custom(s"""| scala-exercises - ${name.value}
-                                       | Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+                                       | Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
                                        |
                                        |""".stripMargin))
     )
diff --git a/src/main/scala/catslib/Applicative.scala b/src/main/scala/catslib/Applicative.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/Apply.scala b/src/main/scala/catslib/Apply.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/ApplyHelpers.scala b/src/main/scala/catslib/ApplyHelpers.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/CatsLibrary.scala b/src/main/scala/catslib/CatsLibrary.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/EitherSection.scala b/src/main/scala/catslib/EitherSection.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/EvalSection.scala b/src/main/scala/catslib/EvalSection.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/Foldable.scala b/src/main/scala/catslib/Foldable.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/FunctorSection.scala b/src/main/scala/catslib/FunctorSection.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/IdentitySection.scala b/src/main/scala/catslib/IdentitySection.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/Monad.scala b/src/main/scala/catslib/Monad.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/MonadHelpers.scala b/src/main/scala/catslib/MonadHelpers.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/Monoid.scala b/src/main/scala/catslib/Monoid.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/OptionTSection.scala b/src/main/scala/catslib/OptionTSection.scala
@@ -0,0 +1,192 @@
+/*
+ *  scala-exercises - exercises-cats
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
+ *
+ */
+
+package catslib
+
+import cats._
+import cats.data.OptionT
+import cats.implicits._
+import org.scalatest.concurrent.ScalaFutures
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+import scala.concurrent.ExecutionContext.Implicits.global
+import scala.concurrent.Future
+
+/**
+ * OptionT is a Monad Transformer that has two type parameters F and A.
+ * F is the wrapping Monad and A is type inside Option. As a result, OptionT[F[_], A] is a light wrapper on an F[Option[A]].
+ * As OptionT is also a monad, it can be used in a for-comprehension and be more convenient to work with than using F[Option[A]] directly.
+ *
+ * @param name OptionT
+ */
+object OptionTSection
+    extends AnyFlatSpec
+    with Matchers
+    with ScalaFutures
+    with org.scalaexercises.definitions.Section {
+
+  implicit val futureOptionEq = new Eq[Future[Option[String]]] {
+    def eqv(x: Future[Option[String]], y: Future[Option[String]]): Boolean =
+      x.futureValue.eqv(y.futureValue)
+  }
+
+  /** If you have only an A and you wish to lift it into an OptionT[F,A], assuming you
+   * have an Applicative instance for F you can use `some` which is an alias for `pure`.
+   * There also exists a none method which can be used to create an OptionT[F,A],
+   * where the Option wrapped A type is actually a None:
+   *
+   * {{{
+   * import scala.concurrent.Future
+   * import scala.concurrent.ExecutionContext.Implicits.global
+   * import cats.implicits._ //imports implicit Applicative[Future]
+   * }}}
+   *
+   */
+  def pureOption(spanishGreetValue: String, englishGreetValue: String, failedGreetValue: String) = {
+    //given
+    val englishGreetOpT: OptionT[Id, String]     = OptionT.some[Id]("Hello")
+    val spanishGreetOpT: OptionT[Future, String] = OptionT.pure[Future]("Hola")
+    val failedGreetOpT: OptionT[Future, String]  = OptionT.none
+
+    //when
+    val englishGreet: Id[String]     = englishGreetOpT.getOrElse("")
+    val spanishGreet: Future[String] = spanishGreetOpT.getOrElse("")
+    val failedGreet: Future[String]  = failedGreetOpT.getOrElse("")
+
+    //then
+    englishGreet shouldBe a[Id[String]]
+    spanishGreet shouldBe a[Future[String]]
+    englishGreet shouldBe (englishGreetValue: String)
+    spanishGreet.futureValue shouldBe (spanishGreetValue: String)
+    failedGreet.futureValue shouldBe (failedGreetValue: String)
+  }
+
+  /** Sometimes you may have an Option[A] and/or F[A] and want to lift them into an OptionT[F, A].
+   * For this purpose OptionT exposes two useful methods, namely fromOption and liftF,
+   * and the standard apply respectively. E.g.:
+   * {{{
+   * val greetingFO: Future[Option[String]] = Future.successful(Some("Hello"))
+   *
+   * val firstnameF: Future[String] = Future.successful("Jane")
+   *
+   * val lastnameO: Option[String] = Some("Doe")
+   * }}}
+   *
+   */
+  def fromOptionT(
+      maybeFrenchGreet: Option[String],
+      maybeItalianGreet: Option[String],
+      maybeFailedGreet: Option[String]) = {
+    //given
+    val frenchGreetFO: Future[Option[String]] = Future.successful(Option("Bonjour"))
+    val italianGreetF: Future[String]         = Future.successful("Ciao")
+    val failedGreetO: Option[String]          = None
+
+    //when
+    val frenchGreetOpT: OptionT[Future, String]  = OptionT(frenchGreetFO)
+    val italianGreetOpT: OptionT[Future, String] = OptionT.liftF(italianGreetF)
+    val failedGreetOpT: OptionT[Future, String]  = OptionT.fromOption(failedGreetO)
+
+    //then
+    assert(frenchGreetOpT === OptionT.fromOption[Future](maybeFrenchGreet))
+    assert(italianGreetOpT === OptionT.fromOption[Future](maybeItalianGreet))
+    assert(failedGreetOpT === OptionT.fromOption[Future](maybeFailedGreet))
+  }
+
+  /**
+   * As you can see, the implementations of all of these variations are very similar.
+   * We want to call the Option operation (map, filter, filterNot, getOrElse),
+   * but since our Option is wrapped in a Future, we first need to map over the Future.
+   * OptionT can help remove some of this boilerplate.
+   * It exposes methods that look like those on Option,
+   * but it handles the outer map call on the Future so we don’t have to:
+   *
+   * {{{
+   * //operating with flattened Future[Option[String]
+   * import scala.concurrent.Future
+   * import scala.concurrent.ExecutionContext.Implicits.global
+   * val customGreeting: Future[Option[String]] = Future.successful(Some("welcome back, Lola"))
+   * val excitedGreeting: Future[Option[String]] = customGreeting.map(_.map(_ + "!"))
+   * val hasWelcome: Future[Option[String]] = customGreeting.map(_.filter(_.contains("welcome")))
+   * val noWelcome: Future[Option[String]] = customGreeting.map(_.filterNot(_.contains("welcome")))
+   * val withFallback: Future[String] = customGreeting.map(_.getOrElse("hello, there!"))
+   *
+   *
+   * //operating with transformer OptionT[Future, String]
+   * import cats.data.OptionT
+   * import cats.implicits._
+   * val customGreetingT: OptionT[Future, String] = OptionT(customGreeting)
+   * val excitedGreeting: OptionT[Future, String] = customGreetingT.map(_ + "!")
+   * val withWelcome: OptionT[Future, String] = customGreetingT.filter(_.contains("welcome"))
+   * val noWelcome: OptionT[Future, String] = customGreetingT.filterNot(_.contains("welcome")) //None
+   * val withFallback: Future[String] = customGreetingT.getOrElse("hello, there!")
+   * }}}
+   *
+   */
+  def optionTMethods(
+      maybeGreet: List[Option[String]],
+      maybeGreetWorld: List[Option[String]],
+      maybeGreetH: List[Option[String]],
+      maybeGreetGuten: List[Option[String]],
+      maybeGreetGutenTag: List[String],
+      maybeGreetGutenAbend: List[String]) = {
+    //given
+    val germanGreetingsLO: List[Option[String]] =
+      List("Hallo".some, "Hi".some, "Guten Morgen".some, none[String])
+    val germanGreetingsT: OptionT[List, String] = OptionT(germanGreetingsLO)
+
+    //when/then (optionT vs flatten)
+    //map
+    germanGreetingsT.map(_ + "!") shouldBe OptionT(maybeGreet: List[Option[String]])
+    germanGreetingsLO.map(_.map(_ + " World!")) shouldBe OptionT(
+      maybeGreetWorld: List[Option[String]]).value
+    //filter
+    germanGreetingsT.filter(_.contains("H")) shouldBe OptionT(maybeGreetH: List[Option[String]])
+    germanGreetingsLO.map(_.filter(_.contains("Guten"))) shouldBe OptionT(
+      maybeGreetGuten: List[Option[String]]).value
+    //getOrElse
+    germanGreetingsT.getOrElse("Guten Tag") shouldBe (maybeGreetGutenTag: List[String])
+    germanGreetingsLO.map(_.getOrElse("Guten Abend")) shouldBe (maybeGreetGutenAbend: List[String])
+    //...
+  }
+
+  /**
+   * OptionT is a Monad, so it has a flatMap method which can be used in a for-comprehension.
+   *
+   * {{{
+   * val greetingFO: Future[Option[String]] = Future.successful(Some("Hello"))
+   *
+   * val firstnameF: Future[String] = Future.successful("Jane")
+   *
+   * val lastnameO: Option[String] = Some("Doe")
+   *
+   * val ot: OptionT[Future, String] = for {
+   *   g <- OptionT(greetingFO)
+   *   f <- OptionT.liftF(firstnameF)
+   *   l <- OptionT.fromOption[Future](lastnameO)
+   * } yield s"$g $f $l"
+   *
+   * val result: Future[Option[String]] = ot.value // Future(Some("Hello Jane Doe"))
+   * }}}
+   *
+   */
+  def forComprehension(maybeOpResult: Option[Double]) = {
+    //given
+    val initialNumber: Future[Option[Double]] = Future(0.0.some)
+
+    //when
+    val opResult: OptionT[Future, Double] = for {
+      a <- OptionT(initialNumber).map(_ + 2)
+      b <- OptionT.liftF(Future(a)).map(_ * 6)
+      c <- OptionT.liftF(Future(b)).map(_ / 8)
+    } yield c
+
+    //then
+    opResult.value.futureValue shouldBe (maybeOpResult: Option[Double])
+
+  }
+}
diff --git a/src/main/scala/catslib/Semigroup.scala b/src/main/scala/catslib/Semigroup.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/Traverse.scala b/src/main/scala/catslib/Traverse.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/TraverseHelpers.scala b/src/main/scala/catslib/TraverseHelpers.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/Validated.scala b/src/main/scala/catslib/Validated.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/main/scala/catslib/ValidatedHelpers.scala b/src/main/scala/catslib/ValidatedHelpers.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/test/scala/catslib/ApplicativeSpec.scala b/src/test/scala/catslib/ApplicativeSpec.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/test/scala/catslib/ApplySpec.scala b/src/test/scala/catslib/ApplySpec.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/test/scala/catslib/EitherSpec.scala b/src/test/scala/catslib/EitherSpec.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/test/scala/catslib/EvalSpec.scala b/src/test/scala/catslib/EvalSpec.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/test/scala/catslib/FoldableSpec.scala b/src/test/scala/catslib/FoldableSpec.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/test/scala/catslib/FunctorSpec.scala b/src/test/scala/catslib/FunctorSpec.scala
@@ -1,6 +1,6 @@
 /*
  *  scala-exercises - exercises-cats
- *  Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>
+ *  Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>
  *
  */
 
diff --git a/src/test/scala/catslib/IdentitySpec.scala b/src/test/scala/catslib/IdentitySpec.scala
diff --git a/src/test/scala/catslib/MonadSpec.scala b/src/test/scala/catslib/MonadSpec.scala
diff --git a/src/test/scala/catslib/MonoidSpec.scala b/src/test/scala/catslib/MonoidSpec.scala
diff --git a/src/test/scala/catslib/OptionTSpec.scala b/src/test/scala/catslib/OptionTSpec.scala
diff --git a/src/test/scala/catslib/SemigroupSpec.scala b/src/test/scala/catslib/SemigroupSpec.scala
diff --git a/src/test/scala/catslib/TraverseSpec.scala b/src/test/scala/catslib/TraverseSpec.scala
diff --git a/src/test/scala/catslib/ValidatedSpec.scala b/src/test/scala/catslib/ValidatedSpec.scala

Original file line number	Diff line number	Diff line change
`@@ -48,7 +48,7 @@ object ProjectPlugin extends AutoPlugin {`
`48`	`48`	`Resolver.sonatypeRepo("releases")`
`49`	`49`	`),`
`50`	`50`	`headerLicense := Some(Custom(s"""\| scala-exercises - ${name.value}`
`51`		`- \| Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>`
	`51`	`+ \| Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>`
`52`	`52`	`\|`
`53`	`53`	`\|""".stripMargin))`
`54`	`54`	`)`
Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,6 @@`
`1`	`1`	`/*`
`2`	`2`	`* scala-exercises - exercises-cats`
`3`		`- * Copyright (C) 2015-2019 47 Degrees, LLC. <http://www.47deg.com>`
	`3`	`+ * Copyright (C) 2015-2020 47 Degrees, LLC. <http://www.47deg.com>`
`4`	`4`	`*`
`5`	`5`	`*/`
`6`	`6`