What should I be returning in a getter method in swift

Question

var userState: UserState {
    get {
        return userState
    }
    set {
        print("\(self.userState)")
    }
}

Returning userState causes an infinite loop. I'm not interested in the getter method and just want to return the value of the property in the getter. I would rather like to customise the setter method.

The answer depends on what you plan to do in the setter. Show your actual setter. — rmaddy, Mar 03 '17 at 16:08
If you absolutely need to override `set` and `get`, keep `userState` public and create a private store `_userState` which the getter and setter read from. — JAL, Mar 03 '17 at 16:11

score 8 · Accepted Answer · answered Mar 03 '17 at 16:12

8

If you would like to override a setter, but keep your property readable, then you need to make a variable to "back" the property:

private var storedUserState: UserState
var userState: UserState {
    get {
        return storedUserState
    }
    set {
        print("Before: \(self.storedUserState)")
        storedUserState = newValue
        print("After: \(self.storedUserState)")
    }
}

If you would like to customize a setter method, but would prefer the property to remain stored, use property observers instead of overriding the accessors:

var userState: UserState = nil {
    willSet(newState) {
        print("About to set userState: \(newState)")
    }
    didSet {
        print("Finished: new=\(userState), old=\(oldValue)")
    }
}

answered Mar 03 '17 at 16:12

Sergey Kalinichenko

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Ohh boy, this contrast is sooo great. I was always confused about these two. @others: the first way is also known as **computed** property – mfaani Mar 03 '17 at 16:34
@Honey I mean, let others use expressions like `if (obj.userState.someField > someValue)`, i.e. providing a getter that returns something useful. Another alternative is to let property getter throw an exception, creating an effectively "write-only" property (not a very good idea; one should go with a method at that point). – Sergey Kalinichenko Mar 03 '17 at 16:46
"property getter throw an exception, creating an effectively "write-only" property" you mean the `get` would look like: `get { fatalError()}` really don't understand where that could be used – mfaani Mar 03 '17 at 16:51
1

@Honey Yes, something like this: `user.password = "12345"` instead of `user.setPassword("12345")` You don't want an ability to write `"password: \(user.password)"` – Sergey Kalinichenko Mar 03 '17 at 16:51

score 3 · Answer 2 · answered Mar 03 '17 at 16:09

Instead of set, what you want is willSet or didSet, which get run before/after the value changes. Then you can omit get.

With willSet, since the variable hasn't changed yet, the new value is available in a parameter called newValue. Conversely, didSet has oldValue.

What should I be returning in a getter method in swift

2 Answers2