SCALA-601 Add code for stackable trait article

Author: Matteo Di Pirro

scala-core-modules/scala-core-8/src/main/scala/com/baeldung/scala/stackabletrait/DecoratorExample.scala

@@ -0,0 +1,43 @@
+package com.baeldung.scala.stackabletrait
+
+object DecoratorExample {
+  trait IntTransformation {
+    def transform(value: Int): Int = value
+  }
+
+  class TransformationDecorator(wrappee: IntTransformation)
+    extends IntTransformation {
+    override def transform(value: Int): Int = wrappee.transform(value)
+  }
+
+  class DoubleDecorator(wrappee: IntTransformation)
+    extends TransformationDecorator(wrappee) {
+    override def transform(value: Int): Int =
+      super.transform(value * 2)
+  }
+
+  class LogInt(wrappee: IntTransformation)
+    extends TransformationDecorator(wrappee) {
+    override def transform(value: Int): Int = {
+      println(s"Transforming value: $value")
+      super.transform(value)
+    }
+  }
+
+  class CustomDecorator(f: Int => Int, wrappee: IntTransformation)
+    extends TransformationDecorator(wrappee) {
+    override def transform(value: Int): Int =
+      super.transform(f(value))
+  }
+
+  @main
+  def mainDec(): Unit = {
+    val identity = new IntTransformation {}
+
+    val withLogging = new LogInt(identity)
+    val withDouble = new DoubleDecorator(withLogging)
+    val withCustom = new CustomDecorator(_ + 1, withDouble)
+
+    println(s"With increment, double, and logging: ${withCustom.transform(5)}")
+  }
+}

scala-core-modules/scala-core-8/src/main/scala/com/baeldung/scala/stackabletrait/MixinExample.scala

@@ -0,0 +1,24 @@
+package com.baeldung.scala.stackabletrait
+
+object MixinExample {
+  trait Person {
+    val name: String
+    val country: String
+  }
+
+  case class ItalianPerson(name: String) extends Person {
+    val country = "Italy"
+  }
+
+  trait WithPrettyPrinting extends Person {
+    def prettyPrint: String =
+      s"""Name: $name
+        |Country: $country""".stripMargin
+  }
+
+  @main
+  def main(): Unit =
+    val italian = new ItalianPerson("Mario") with WithPrettyPrinting
+    println(italian)
+    println(italian.prettyPrint)
+}

scala-core-modules/scala-core-8/src/main/scala/com/baeldung/scala/stackabletrait/StackableTraitExample.scala

@@ -0,0 +1,41 @@
+package com.baeldung.scala.stackabletrait
+
+object StackableTraitExample {
+  trait IntTransformation {
+    def transform(value: Int): Int = value
+  }
+
+  trait DoubleTransformation extends IntTransformation {
+    override def transform(value: Int): Int =
+      super.transform(value * 2)
+  }
+
+  trait LogInt extends IntTransformation {
+    override def transform(value: Int): Int = {
+      println(s"Transforming value: $value")
+      super.transform(value)
+    }
+  }
+
+  trait CustomTransformation(f: Int => Int) extends IntTransformation {
+    override def transform(value: Int): Int =
+      super.transform(f(value))
+  }
+
+  @main
+  def mainST(): Unit = {
+    val logAndDouble = new IntTransformation
+      with DoubleTransformation
+      with LogInt {}
+    val doubleAndLog = new IntTransformation
+      with LogInt
+      with DoubleTransformation {}
+    val logAndCustom = new IntTransformation
+      with CustomTransformation(_ + 1)
+      with LogInt {}
+
+    println(s"Log and double: ${logAndDouble.transform(5)}")
+    println(s"Double and log: ${doubleAndLog.transform(5)}")
+    println(s"Log and increment: ${logAndCustom.transform(5)}")
+  }
+}