CODESAMPLE

Mediator - Scala

Mediator Scala

The Mediator pattern defines an object that encapsulates how a set of objects interact. This promotes loose coupling by preventing objects from referring to each other explicitly, and it lets you vary their interactions independently. In this Scala example, ChatMediator mediates communication between User objects. Each user registers with the mediator and sends messages to the mediator, which then distributes them to the appropriate recipients. Scala’s case classes and traits are well-suited for defining the components. Using an abstract Mediator allows flexibility for different mediation strategies, and is a common functional approach to structuring interactions.

trait Mediator {
  def sendMessage(message: String, user: User): Unit
}

case class User(name: String, mediator: Mediator) {
  def send(message: String): Unit = {
    mediator.sendMessage(message, this)
  }

  def receive(message: String): Unit = {
    println(s"${name} received: ${message}")
  }
}

class ChatMediator extends Mediator {
  private var users: List[User] = List.empty

  override def sendMessage(message: String, user: User): Unit = {
    println(s"${user.name} sends: ${message}")
    users.filter(_ != user).foreach(_.receive(message))
  }

  def addUser(user: User): Unit = {
    users = user :: users
  }
}

object MediatorExample extends App {
  val mediator = new ChatMediator()
  val alice = User("Alice", mediator)
  val bob = User("Bob", mediator)
  val charlie = User("Charlie", mediator)

  mediator.addUser(alice)
  mediator.addUser(bob)
  mediator.addUser(charlie)

  alice.send("Hello everyone!")
  bob.send("Hi Alice!")
  charlie.send("What's up?")
}