Asteroid vs. Spaceship

gistfile1.scala

class Asteroid
class Spaceship

trait Collidable[A, B] {
	def collideWith(a: A, b: B): String
}

implicit object CollidableAsteroidWithAsteroid extends Collidable[Asteroid, Asteroid] {
	def collideWith(a: Asteroid, b: Asteroid) =
		"what happens when an asteroid collides with an asteroid"
}

implicit object CollidableAsteroidWithSpaceship extends Collidable[Asteroid, Spaceship] {
	def collideWith(a: Asteroid, b: Spaceship) =
		"what happens when an asteroid collides with a spaceship"
}

implicit object CollidableSpaceshipWithAsteroid extends Collidable[Spaceship, Asteroid] {
	def collideWith(a: Spaceship, b: Asteroid) =
		"what happens when a spaceship collides with an asteroid"
}

implicit object CollidableSpaceshipWithSpaceship extends Collidable[Spaceship, Spaceship] {
	def collideWith(a: Spaceship, b: Spaceship) =
		"what happens when a spaceship collides with a spaceship"
}

def collideWith[A, B](a: A, b: B)(implicit ev: Collidable[A, B]): String =
	ev.collideWith(a, b)

val a1 = new Asteroid
val a2 = new Asteroid
val s1 = new Spaceship
val s2 = new Spaceship

// Static dispatch only

println(collideWith(a1, s1))
println(collideWith(s2, s1))

class BlueAsteroid extends Asteroid

// leads to an error: could not find implicit value for parameter ev
println(collideWith(new BlueAsteroid, s1))