structuraltypes.scala

type Quackable = {
  def quack(): Unit
}

def listenToSomeQuacking(x: Quackable){
  println("Gosh I love the sound of quacks")
  x.quack()
}

class Duck{
  def quack(){
    println("Quack!")
  }
}

class Dog{
  def bark(){
    println("Woof!")
  }
}

listenToSomeQuacking(new Duck)

listenToSomeQuacking(new Dog) // compile error