How to decompose my own sequence ADT in Scala?

Asked Oct 16 '20 at 11:25

Active Oct 16 '20 at 11:25

Viewed 36 times

As an example I have a Sequence like this

  abstract class MySeq[+A] {
    def head: A = ???
    def tail: MySeq[A] = ???
  }
  case object EmptySeq extends MySeq[Nothing]
  case class Cons[+A](override val head: A, override val tail: MySeq[A]) extends MySeq[A]
  object MySeq {
    def unapply[A](arg: MySeq[A]): Option[Seq[A]] = ???
  }

and I wanted to do pattern matching in this ADT.

For instance

  val mySeq: MySeq[Int] = Cons(1, Cons(2, Cons(3, EmptySeq)))
  val decomposed = mySeq match {
    case MySeq(1, 2, _*) => "starting with 1, 2"
    case _ => "something else"
  }

  println(decomposed)

But this give an error: Wrong number of arguments for extractor found 3 expected 1

I miss something.

is it possible to do this?

asked Oct 16 '20 at 11:25

Chema

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What is that `_*` supposed to mean? – Tim Oct 16 '20 at 11:33
2

@Tim this is standard syntax https://scastie.scala-lang.org/DmytroMitin/TmvfxSTgSDONOA4agpcLAg – Dmytro Mitin Oct 16 '20 at 11:38
2

@Chema probably you want `unapplySeq` – Dmytro Mitin Oct 16 '20 at 11:38
2

https://stackoverflow.com/questions/8282277/what-is-the-difference-between-unapply-and-unapplyseq – Dmytro Mitin Oct 16 '20 at 11:40
@DmytroMitin, thanks a lot. You posted a link that answers my question. – Chema Oct 16 '20 at 11:55

How to decompose my own sequence ADT in Scala?

0 Answers0