CODESAMPLE

Command - Scala

Command Scala

The Command pattern encapsulates a request as an object, allowing for parameterization of clients with different requests, queueing or logging of requests, and support for undoable operations. This Scala example uses a functional style with traits and case classes to define the command interface and concrete commands. Order is the invoker, accepting and executing OrderCommands. The Command trait defines the execute method. Idiomatic Scala is used with immutability (case classes) and leveraging functional composition to represent actions. No mutable state is used within the commands themselves, enhancing testability and concurrency.

trait Command {
  def execute(): String
}

case class AddItemCommand(order: Order, item: String) extends Command {
  override def execute(): String = {
    order.addItem(item)
    s"Added $item to the order."
  }
}

case class RemoveItemCommand(order: Order, item: String) extends Command {
  override def execute(): String = {
    order.removeItem(item)
    s"Removed $item from the order."
  }
}

case class Order(items: List[String] = List.empty) {
  def addItem(item: String): Order = Order(item :: items)
  def removeItem(item: String): Order = Order(items.filter(_ != item))
  def listItems():String = items.mkString(", ")
}

object CommandExample {
  def main(args: Array[String]): Unit = {
    val myOrder = Order()
    val addItem1 = AddItemCommand(myOrder, "Shirt")
    val addItem2 = AddItemCommand(myOrder, "Pants")
    val removeItem = RemoveItemCommand(myOrder, "Shirt")

    println(addItem1.execute())
    println(addItem2.execute())
    println(removeItem.execute())
    println(s"Current order: ${myOrder.listItems()}")
  }
}