CODESAMPLE

Decorator - Scala

Decorator Scala

The Decorator pattern dynamically adds responsibilities to an object. It provides a flexible alternative to subclassing for extending functionality. Here, we define a base Beverage trait and concrete implementations like Espresso. Decorators, also traits, wrap a Beverage and add cost and description. MilkDecorator and SoyDecorator are examples. The main method demonstrates how to compose decorators to create a beverage with varying additions. This implementation is idiomatic Scala due to its use of traits for defining types and composition over inheritance, aligning with Scala’s functional and object-oriented strengths.

trait Beverage {
  val cost: Double
  val description: String
}

class Espresso extends Beverage {
  val cost = 2.0
  val description = "Espresso"
}

trait BeverageDecorator extends Beverage {
  protected var decoratedBeverage: Beverage
  def this(beverage: Beverage) = {
    this.decoratedBeverage = beverage
    this
  }
}

class MilkDecorator(beverage: Beverage) extends BeverageDecorator {
  val cost = beverage.cost + 0.5
  val description = beverage.description + ", Milk"
}

class SoyDecorator(beverage: Beverage) extends BeverageDecorator {
  val cost = beverage.cost + 0.7
  val description = beverage.description + ", Soy"
}

object Main {
  def main(args: Array[String]): Unit = {
    val espresso = new Espresso()
    val milkEspresso = new MilkDecorator(espresso)
    val soyMilkEspresso = new SoyDecorator(milkEspresso)

    println(s"Description: ${soyMilkEspresso.description}")
    println(s"Cost: $${soyMilkEspresso.cost}")
  }
}