Wibble.scala

object T {
  implicit def XIntToInt(x: XInt): Int = x.n

  // isomorphism to Int
  case class XInt(n: Int)
 
  case class Wibble[A](a: A) {
    def wibble(implicit ev: A <:< Int) = a + 9

    def map[B](f: A => B) =
      Wibble(f(a))
  }
 
  object Wobble {
    def wobble[A](w: Wibble[A])(implicit ev: A => Int) =
      w.map(x => ev(x)).wibble

    implicit def wibblable[A](w: Wibble[A])(implicit ev: A => Int): Wibble[Int] =
      w.map(x => ev(x))
      
    val w1 = Wibble(3)
    // fine
    w1.wibble
    val w2 = Wibble(XInt(3))

    // one of:
    wobble(w2)
    (w2: Wibble[Int]).wibble
  }
 
}