SIP - Sealed Types

Scala Improvement Process
12

Very interesting idea.

Not sure if it’s a bug in the SIP example but you have:

given TypeTest[Int, Num] = (n: Int) => if ((n: Num).ordinal == -1) None else Some(n)

where as you’re proposing to synthesise:

extension (n: Num):
  def ordinal: Int = (n: Int) match {
    case 0          => 0
    case n if n > 0 => 1
    case _          => 2
  }

which will never return -1. Is this because the sugared declaration has a catch-all in it, and that a catch-all of -1 would be synthesised otherwise, or something?