Remark on listing 20.26 and exhaustiveness

Not only the compiler requires a default case for both switch and catch but it imposes this default case to be the last case. For switch, if a case: occurs after default:, the compiler raises an error whereas for catch it only raises a warning telling that the next catch will be never executed.
The following code works but the case “division by 1” is never executed.

enum Error: Swift.Error {
    case divisionBy0
    case divisionBy1
func div(num: Int, den: Int) throws-> Double {
    guard den != 0 else {
        throw Error.divisionBy0
    guard den != 1 else {
        throw Error.divisionBy1
    return Double(num/den)
do {
    let x = try div(num:16, den:1)
    print("Result: \(x)")
} catch Error.divisionBy0 {
    print("Division by 0")
} catch {
    print("General error")
} catch Error.divisionBy1 {
    print("Division by 1 is useless")