50 Matching generic types

The two Box cases distinguish Box<Integer> from Box<String> at runtime and expose an appropriately typed item inside each branch.

class Box<T> {
  T item
}

String describe(Any candidate) {
  return switch candidate {
    case Box<Integer> box { break "number: ${box.item}" }
    case Box<String> box { break "text: ${box.item}" }
    case _ { break "other" }
  }
}

main() {
  Any number = Box<Integer>(item: 7)
  Any text = Box<String>(item: "Norm")
  printLine(describe(candidate: number))
  printLine(describe(candidate: text))
}

Expected output:

number: 7
text: Norm

Try it: Add a Box<Boolean> candidate and predict the final branch.

Precise rules: Reference.