Hands-On Swift 5 Microservices Development

Future enum cases

Imagine you have an enum :

enum ConnectionError: Error {    case timeout    case badRequest}

If you are checking an error from a result, you will do it like this:

switch (error) {    case .timeout:        print("timeout")    case .badRequest:        print("bad request")    default:        print("another request")

As frameworks and libraries develop, the ConnectionError enum could be extended by a future version of a framework or library. Adding another case to the enum could look like this:

enum ConnectionError: Error {    case timeout    case badRequest    case denied}

If a newer version of a framework updates this, it will cause your old code to select the default case, and you would not even notice that there is a new case. By adding a little attribute, @unkown ...