In didSet for an enum property in Swift is it possible to check if the new value is the same as the old one?

Question

Given the following example:

enum ViewState {
    case idle
    case loading
    case caseWithAssociatedValue(String)    
}

class View {
    private var state: ViewState = .idle

    func setState(to state: ViewState) {
        guard state != self.state else { return }
        self.state = state
    }
}

I can't compare two properties of type ViewState and I can't use a raw value to compare as one of my cases has an associated value.

What I'm looking for is a way to check if the new value for state a new value or the same as the current value. Is this possible?

Why the method take state type "State" and the class var state type "ViewState"? — Moayad Al kouz, Apr 22 '18 at 13:56

Joakim Danielson · Accepted Answer · 2018-04-22T14:27:28.980

1

Use willSet and do something like this

enum State : Equatable {
  case idle
  case active
  case done(String)
}

class test {
  var x: State {  
    willSet {
      if x != newValue {
        print("\(x) -> \(newValue)")
      }
    }
  }

  init(_ x: State) {
    self.x = x
  }
}

let t = test(State.idle)
t.x = State.active
t.x = State.done("We're done")

Output is
idle -> active
active -> done("We\'re done")

edited Apr 22 '18 at 14:27

answered Apr 22 '18 at 13:44

Joakim Danielson

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I am curious why this was down voted? Is it wrong or inefficient or what? – Joakim Danielson Apr 22 '18 at 14:09
Your answer did not answer the question, which was how to compare two enums. – mike Apr 22 '18 at 14:18
Ok, got it. I thought the question was about comparing the old vs the new value and not specifically how to do it for an enum. – Joakim Danielson Apr 22 '18 at 14:20
No worries, looking back I could have been a bit clearer in my final sentence. I'll make sure to be less ambiguous in future questions. – mike Apr 22 '18 at 14:22
1

My code works with an enum if it implements Equatable so I'll update it. – Joakim Danielson Apr 22 '18 at 14:24

In didSet for an enum property in Swift is it possible to check if the new value is the same as the old one?

1 Answers1