SE-0192 — Non-Exhaustive Enums — review #2

Evolution Proposal Reviews
15

In addition, it was previously noted that if case pattern matching doesn't make sense when used with unknown pattern, as 'there is no way to prevent it from producing a warning'.

But if you treat switch as a sequence of if-else statements, it becomes clear that:

  1. it doesn't make sense to use the unknown pattern in the first case of a switch statement as well;
  2. it makes perfect sense to use the unknown pattern after all known cases were considered in the sequence of if-else statements.
struct Example {
  func inspect(paperSize newValue: PaperSize) {
    if newValue == .usLetter || newValue == .a4 {
      print("usLetter or a4")

      // use normal pattern matching for the known enum case
    } else if case .photo4x6 = newValue {
      print("photo4x6")

      // use new pattern matching for the unknown enum case
      // no warning produced, because all known enum cases have been matched
    } else if case ._(let rawValue) = newValue {
      print("an unknown case with an associated value \(rawValue)")
    }
  }
}