Duck typing example..

DuckTyping.scala

class Program {
  def run(): Unit = println("I pass a Turing test.")
}

class Person {
  def run(): Unit = println("But I don't.")
}

class Engine {
  def run(): String = "I run in a totally different way"
}

object DuckTyping {
  def makeRun(runner: { def run(): Unit }): Unit = runner.run
  
  val a = new Program
  val b = new Person
  val c = new Engine
  val d = new Object
  
  makeRun(a)
  makeRun(b)
  //makeRun(c) //Won't compile
  //makeRun(d) //Won't compile
}

DuckTyping2.scala

class Program {
  def run(): Unit = println("I pass a Turing test.")
}

class Person {
  def run(): Unit = println("But I don't.")
}

class Engine {
  def run(): String = "I run in a totally different way"
}

object DuckTyping {
  type CanRun = {
    def run(): Unit
  }
  def makeRun(runner: CanRun): Unit = runner.run
  
  val a = new Program
  val b = new Person
  val c = new Engine
  val d = new Object
  
  makeRun(a)
  makeRun(b)
  //makeRun(c) //Won't compile
  //makeRun(d) //Won't compile
}