Scala example source code file (typesafecons.scala)

This example Scala source code file (typesafecons.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

cons, cons, doesn't, end, end, first, nothing, pair, pair, second, t, t1, t2, t2

The Scala typesafecons.scala source code

object Pair {
 sealed trait Pair {
   type First
   type Second <: Pair
 }

 class End extends Pair {
   type First = Nothing
   type Second = End

   def ::[T](v : T) : Cons[T, End] = Cons(v, this)
 }

 case object End extends End

 final case class Cons[T1, T2 <: Pair](_1 : T1, _2 : T2) extends Pair {
   type First = T1
   type Second = T2

   def ::[T](v : T) : Cons[T, Cons[T1, T2]] = Cons(v, this)
   def find[T](implicit finder : Cons[T1, T2] => T) = finder(this)
 }

 implicit def findFirst[T1, T2 <: Pair] : Cons[T1, T2] => T1 = (p : Cons[T1, T2]) => p._1
 implicit def findSecond[T, T1, T2 <: Pair](implicit finder : T2 => T) : Cons[T1, T2] => T = (p : Cons[T1, T2]) => finder(p._2)

 val p : Cons[Int, Cons[Boolean, End]] = 10 :: false :: End
// val x : Boolean = p.find[Boolean](findSecond(findFirst))
 val x2 : Boolean = p.find[Boolean]  // Doesn't compile
}