Some playing around Scala's type classes

typeclasses.scala

def foo[A](a: A)(implicit ma: HasSize[A]) = {
  ma.size(a)
}

def boo[A : HasSize](a: A) = {
  implicitly[HasSize[A]].size(a)
}

trait HasSize[-A] { def size(a: A): Int }

class Shoe { def size = 5 }

implicit object ShoeSize extends HasSize[Shoe] {
  def size(s: Shoe) = s.size + 1
}

implicit object ListSize extends HasSize[List[_]] {
  def size(a: List[_]) = a.size
}

val l = foo(List(1, 2, 3, 4))
val bb = boo(List(1,2,3))

val s = new Shoe
val s1 = ShoeSize

val x = foo(s)(s1)
val x2 = foo(s)