Externalizing configuration values using the Cake Pattern

cakeConfig.scala

/* Standard component trait a-la cake */
trait MessagePrinterComponent {

  def printer: MessagePrinter

  trait MessagePrinter{
    def printMessage(message: String)
  }
}

/* A trait to encapsulate implementation-specific configuration */
trait MessagePrinterConfig {
  val borderChar: String
}

/* The component implementation and trait wrapper a-la cake */
trait MyMessagePrinterComponent extends MessagePrinterComponent {
  this: MessagePrinterConfig =>

  def printer = new MyMessagePrinter
  
  class MyMessagePrinter extends MessagePrinter {
    def printMessage(message: String) = {
      val border = borderChar * (message.length + 4)
      println(border)
      println(borderChar + " " + message + " " + borderChar)
      println(border)
    }
  }
}

/* The actual configuration we'll use which could be put perhaps in a "config" package */
trait MyMessagePrinterConfig extends MessagePrinterConfig{
  val borderChar = "*"
}

/* The app which demonstrates using the component with its configuration */
object Cli extends App {  
  
  val printerComponent = new MyMessagePrinterComponent with MyMessagePrinterConfig

  printerComponent.printer.printMessage("foobar")
}