Mix-ins – rich interfaces

Let's add a funny twist to the tale. We will now remove the NameIt trait and change both the traits, as shown in the following code:

   trait Walks {
    def name : String
    def walk() =
      println(name + "" is having a stroll now"")
  }
  trait GoodsMover {
    def name : String
    def moveGoods() =
      println(name + "" busy moving heavy stuff"")
  }

The name() method, referred to by the traits, must be defined somewhere. As long as Horse and Donkey define the name() method, it works.

Writing a rating comparison algorithm for our animals illustrates one major use of the traits. Our rating is a simple number. Try the following snippet to implement the compare method:

object CompareAnimals extends App {
  // traits Walks and GoodsMover not shown
  abstract class Animal(val rating: Int) extends Ordered[Animal]

  class Horse(rating: Int) extends Animal(rating) with Walks { // 1
    override def name(): String = ""Horse""
    override def compare(that: Animal...