Union type subtyping in Scala

Question

I can do following easily with Dotty:

trait Ex {type T <: Int | Seq[Int]; def f:T}

trait Ex2 extends Ex {override type T = Seq[Int]; override def f = Seq(2)}

trait Ex3 extends Ex {override type T = Int; override def f = 2}

How can I do union type subtyping without Dotty?

My question is quite different from "how to implement everything you can do with dotty without dotty". — Alexander Chepurnoy, Jul 06 '16 at 17:35
Type disjunctions are already hard, but I imagine you could make subtypes work if you hated yourself enough: http://stackoverflow.com/questions/3508077/how-to-define-type-disjunction-union-types/21054507 — J Cracknell, Jul 07 '16 at 05:56

score 1 · Answer 1 · answered Jul 06 '16 at 16:02

1

The simple solution is the upper bound type:

trait Ex {type T >: Int with Seq[Int]; def f:T}

trait Ex2 extends Ex {override type T = Seq[Int]; override def f = Seq(2)}

trait Ex3 extends Ex {override type T = Int; override def f = 2}

answered Jul 06 '16 at 16:02

Alexander Chepurnoy

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Union type subtyping in Scala

1 Answers1