Scala example source code file (unapplyNeedsMemberType.scala)

This example Scala source code file (unapplyNeedsMemberType.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

any, any, app, app, cons, gunk, join, joinseq, joinseq, option, seq, seq, some

The Scala unapplyNeedsMemberType.scala source code

// error with -Xunapply, (because of missing call to memberType?)

trait Gunk[a] {

  type Seq

  object Cons {
    def unapply(s: Seq) = unapply_Cons(s)
  }
  def unapply_Cons(s: Any): Option[Tuple2[a, Seq]]
}  

class Join[a] extends Gunk[a] {
  type Seq = JoinSeq

  abstract class JoinSeq
  case class App(xs: Seq, ys: Seq) extends JoinSeq

  def append(s1: Seq, s2: Seq): Seq = s1 // mock implementation

  def unapply_Cons(s: Any) = s match {
    case App(Cons(x, xs), ys) => Some(Pair(x, append(xs, ys)))
    case _ => null
  }
}