Swift Switch case “not”

Question

I\'ve got two enums:

public enum ServerState {
  case Connecting
  case Open
  case LoggedIn
  case Closed
  case Error(NSError)
}

enum TransportLayerState          


        

Answer 1

One possible answer I found was to make TransportLayerState equatable. In that case I could do this:

switch serverState {
case .Connecting where tlState != .Connecting: return false
case .Closed where tlState != .Disconnected(nil): return false
case let .Error(err) where tlState != .Diconnected(err): return false
...
default: return true
}

I do end up having to write a bit of code in TransportLayerState enum to make it equatable, so not sure if it's worth the effort, but it does work.

Answer 2

Since all patterns are checked sequentially (and the first match "wins"), you could do the following:

switch (serverState, tlState) {

case (.Connecting, .Connecting): return true // Both connecting 
case (.Connecting, _): return false  // First connecting, second something else

case (.Closed, .Disconnected(.None)): return true
case (.Closed, _): return false

// and so on ...

So generally, matching a case where one of the state is not a specific state can be done with two patterns: The first matches the state, and the second is the wildcard pattern (_) which then matches all other cases.