Set a default value for a property with defined getter and setter

Question

I have a very simple class

class SimpleClass {
    var simpleDescription: String {
    get {
        return self.simpleDescription
    }
    set {
        self.simpleDescription = newValue
    }
    }
}

What is the correct way to define a default value for the simpleDescription variable?

Answer 1

In Swift, getters and setters are used for computed properties - there is no storage for the property and thus, in your case, simpleDescription can't be set in a setter.

If you need a default value, use:

class SimpleClass {
  var simpleDescription: String = "default description"
}

if you want to initialize use:

class SimpleClass {
  var simpleDescription: String
  init (desc: String) {
    simpleDescription = desc
  }
}

Answer 2

If what you want is to perform an action each time a variable is set or just to check if the value is correct you can use Property Observers
From docs:

Property observers observe and respond to changes in a property’s value. Property observers are called every time a property’s value is set, even if the new value is the same as the property’s current value.

You can use them like this:

class StepCounter {
    var totalSteps: Int = 0 {
        willSet(newTotalSteps) {
            print("About to set totalSteps to \(newTotalSteps)")
        }
        didSet {
            if totalSteps > oldValue  {
                print("Added \(totalSteps - oldValue) steps")
            }
        }
    }
}

EDIT

Looks like this doesn't work when overriding inherited properties. Here is an example of what you can't do:

class StepWihtoutCounter {
    var totalSteps: Int = 0 
}

class StepCounter: StepWihtoutCounter {
    override var totalSteps: Int = 0 {
        willSet(newTotalSteps) {
            print("About to set totalSteps to \(newTotalSteps)")
        }
        didSet {
            if totalSteps > oldValue  {
                print("Added \(totalSteps - oldValue) steps")
            }
        }
    }