A taste of the cake pattern

Scala provides a nice way to inject dependencies via a feature called self-annotation. This is useful to inject dependencies. Consider the giveInnoculation() method in Animal, as shown here:

object ScalaDepInj extends App {

  abstract class Animal(val rating: Int, var inoculated:
  Boolean = false) {
    def name(): String

    def alreadyInoculated() = inoculated

    def setInoculated(b: Boolean) = {
      inoculated = b
    }
  }

  trait Vet { // 1
    def name(): String

    def inoculate(animal: Animal) = {
      println(""Innoculating "" + animal.name)
    }
  }
  trait ChoosyVet extends Vet { // 2
    def alreadyInoculated(): Boolean

    abstract override def inoculate(animal: Animal) = {
      if (!alreadyInoculated()) // filter out already
      // inoculated animals
        println(""Innoculating "" + animal.name)
    }
  }

  trait Inoculate {
    this: Animal with Vet => // 3
    def setInoculated(b: Boolean)

    def giveInoculation() = {
 ...