Can an enum contain another enum values in Swift?

Question

I'd like to share some enum properties. Something like:

enum State {
  case started
  case succeeded
  case failed
}

enum ActionState {
  include State // what could that be?
  case cancelled
}

class Action {
  var state: ActionState = .started

  func set(state: State) {
    self.state = state
  }

  func cancel() {
    self.state = .cancelled
  }
}

I see why ActionState can not inherit from State (because the state cancelled has no representation in State) but I want to still be able to say "ActionState is like State with more options, and ActionState can get inputs that are of type State, because they are also of type ActionState"

I see how I could get the above logic to work with copying the cases in ActionState and having a switch in the set function. But I'm looking for a better way.

I know enum can't inherit in Swift, and I've read the protocol answer of swift-enum-inheritance. It doesn't address the need for "inheriting" or including cases from another enum, but only properties and variables.

Answer 1

Details

• Swift 4, 3
• Xcode 10.2.1 (10E1001), Swift 5 (Last revision of this post)

Solution

enum State {
    case started, succeeded, failed
}

enum ActionState {
    case state(value: State), cancelled
}

class Action {
    var state: ActionState = .state(value: .started)
    func set(state: State) { self.state = .state(value: state) }
    func cancel() { state = .cancelled }
}

Full Sample

Do not to forget to paste the solution code

import Foundation

extension Action: CustomStringConvertible {
    var description: String {
        var result = "Action - "
        switch state {
            case .state(let value): result += "State.\(value)"
            case .cancelled: result += "cancelled"
        }
        return result
    }
}

let obj = Action()
print(obj)
obj.set(state: .failed)
print(obj)
obj.set(state: .succeeded)
print(obj)
obj.cancel()
print(obj)

Result

//Action - State.started
//Action - State.failed
//Action - State.succeeded
//Action - cancelled