Multiple dispatch experiment

gistfile1.scala

class MMethod[M, A1, A2, R](f: (A1, A2) => R) {                                                                      
  def apply(a1: A1, a2: A2): R = f(a1, a2)
}

class MultiMethod {
  def apply[A1, A2, R](a1: A1, a2: A2)
                      (implicit mm: MMethod[this.type, A1, A2, R]): R =
    mm(a1, a2)

  // use a singleton type to attach the resulting implicit to our multimethod
  def add[A1, A2, R](f: (A1, A2) => R): MMethod[this.type, A1, A2, R] =
    new MMethod[this.type, A1, A2, R](f)
}

case class Asteroid()
case class Starship()

object Main {
  val collide = new MultiMethod

  implicit val mm1 = collide add {
    (a1: Asteroid, a2: Asteroid) => "Two asteroids collide"
  }

  implicit val mm2 = collide add {
    (s: Starship, a: Asteroid) =>  "Starship shoots asteroid"
  }

  // in soviet russia…
  val collideInSovietRussia = new MultiMethod

  // clojure likes mating bunnies
  implicit val mm3 = collideInSovietRussia add {
    (a1: Asteroid, a2: Asteroid) => "Two asteroids mate… WTF!?!?!?"
  }

  implicit val mm4 = collideInSovietRussia add {
    (s: Starship, a: Asteroid) =>  "Asteroid shoots starship… erm yeah… right"
  }

  def main(args: Array[String]) {
    println(collide(Asteroid(), Asteroid()))
    println(collide(Starship(), Asteroid()))
    println(collideInSovietRussia(Asteroid(), Asteroid()))
    println(collideInSovietRussia(Starship(), Asteroid()))
  }
}