39 Switch results

switch can produce a result while extracting an enum variant's payload.

enum Result {
  Success(Integer count),
  Failure(String reason)
}

String describe(Result result) {
  return switch result {
    case Success(Integer count) { break "${count} items" }
    case Failure(String reason) { break reason }
  }
}

main() {
  printLine(describe(result: Result.Success(count: 3)))
  printLine(describe(result: Result.Failure(reason: "empty")))
}

Expected output:

3 items
empty

Each case binds the matching payload and exits with break followed by a string. The function returns that switch result; a statement switch would not need a result value.

Try it: Change the Success branch to include a label before the count.

Precise rules: Reference.