Switch to Scala 3 enum style

cheat-sheet.md

@@ -131,16 +131,14 @@ The values of a product type typically contain several values, called fields. Fo
 Values of algebraic types are analysed with pattern matching, which identifies a value by its constructor or field names and extracts the data it contains.
 
 ### Sealed trait
-When defining an algebraic data type using sealed traits, it allows the compiler to exhaustively check the possible cases in match expressions.
+When defining an algebraic data type using enums, it allows the compiler to exhaustively check the possible cases in match expressions.
 The compiler will emit a warning (or an error is the option "-Xfatal-warnings" option is enabled) if you have missed a specific case.
 The compiler knows all of the subtypes of the trait that can possibly exist as they can only be extended in the file.
 
 ```scala
-sealed trait MyBooleanType
-
-case object True extends MyBooleanType
-
-case object False extends MyBooleanType
+enum MyBooleanType {
+  case True, False
+}
 ```
 
 ### Pattern matching

src/main/scala/introcourse/level02/TypesExercises.scala

@@ -175,17 +175,24 @@ object TypesExercises {
     *
     * You can read the following as a `TrafficLight` is either `Red` or `Yellow` or `Green`.
     *
-    * A sealed trait can only be extended in the same file that it is defined.
+    * A sealed trait / enum can only be extended in the same file that it is defined.
     *
     * This technique helps you make invalid states/values irrepresentable in your programs
     */
+  enum TrafficLight {
+    case Red, Yellow, Green
+  }
+
+  // Scala 2.12 equivalent syntax
+  /*
   sealed trait TrafficLight
 
   case object Red extends TrafficLight
 
   case object Yellow extends TrafficLight
 
   case object Green extends TrafficLight
+   */
 
   /**
     * scala> showTrafficLight(Red)

src/main/scala/introcourse/level03/package.scala

@@ -4,12 +4,8 @@ package object level03 {
 
   case class Person(name: String, age: Int)
 
-  sealed trait TrafficLight
-
-  case object Red extends TrafficLight
-
-  case object Yellow extends TrafficLight
-
-  case object Green extends TrafficLight
+  enum TrafficLight {
+    case Red, Yellow, Green
+  }
 
 }

src/main/scala/introcourse/level04/package.scala

@@ -4,12 +4,8 @@ package object level04 {
 
   case class Person(name: String, age: Int)
 
-  sealed trait TrafficLight
-
-  case object Red extends TrafficLight
-
-  case object Yellow extends TrafficLight
-
-  case object Green extends TrafficLight
+  enum TrafficLight {
+    case Red, Yellow, Green
+  }
 
 }

src/main/scala/introcourse/level05/EitherExercises.scala

@@ -9,13 +9,11 @@ import ExceptionExercises.personStringPairs
 object EitherExercises {
 
   //ADT for representing errors as values
-  sealed trait AppError
-
-  case object EmptyName extends AppError
-
-  case class InvalidAgeValue(value: String) extends AppError
-
-  case class InvalidAgeRange(age: Int) extends AppError
+  enum AppError {
+    case EmptyName
+    case InvalidAgeValue(value: String)
+    case InvalidAgeRange(age: Int)
+  }
 
   /**
     * In the ExceptionExercises exercise we used Exceptions to handle validation and

src/main/scala/introcourse/level07/LogParser.scala

@@ -35,7 +35,9 @@ object LogParser {
     * - Warning
     * - Error with (severity: Int)
     */
-  sealed trait LogLevel
+  enum LogLevel {
+    case TODO // enums must have as least one case, replace this when you are ready
+  }
 
   /**
     * Now create an ADT for `LogMessage`, where `LogMessage` can be one of two possibilities:
@@ -44,7 +46,9 @@ object LogParser {
     */
   type Timestamp = Int
 
-  sealed trait LogMessage
+  enum LogMessage {
+    case TODO // enums must have as least one case, replace this when you are ready
+  }
 
  /**
    * Once you have defined your data types, remove `import Types._` from

src/test/scala/introcourse/level02/TypesExercisesTest.scala

@@ -1,6 +1,7 @@
 package introcourse.level02
 
-import introcourse.level02.TypesExercises._
+import introcourse.level02.TypesExercises.*
+import introcourse.level02.TypesExercises.TrafficLight.*
 import org.scalactic.TypeCheckedTripleEquals
 import org.scalatest.funspec.AnyFunSpec
 

src/test/scala/introcourse/level04/NullExercisesTest.scala

@@ -1,6 +1,7 @@
 package introcourse.level04
 
-import introcourse.level04.NullExercises._
+import introcourse.level04.NullExercises.*
+import introcourse.level04.TrafficLight.*
 import org.scalactic.TypeCheckedTripleEquals
 import org.scalatest.funspec.AnyFunSpec
 

src/test/scala/introcourse/level04/OptionExercises1Test.scala

@@ -1,6 +1,7 @@
 package introcourse.level04
 
-import introcourse.level04.OptionExercises1._
+import introcourse.level04.OptionExercises1.*
+import introcourse.level04.TrafficLight.*
 import org.scalactic.TypeCheckedTripleEquals
 import org.scalatest.funspec.AnyFunSpec
 

src/test/scala/introcourse/level05/EitherExercisesTest.scala

@@ -1,6 +1,7 @@
 package introcourse.level05
 
-import introcourse.level05.EitherExercises._
+import introcourse.level05.EitherExercises.*
+import introcourse.level05.EitherExercises.AppError.*
 import org.scalactic.TypeCheckedTripleEquals
 import org.scalatest.funspec.AnyFunSpec