I don't understand the meaning of this error. This is what I am trying to do:
protocol P {
var testTitle: String? { get }
}
class MyViewController: UIViewController, P {
var testTitle: String? {
didSet {
self.title = testTitle
}
}
}
final class TestViewController: MyViewController {
var testTitle: String? { // Error occurs here
return "Test"
}
}
And I'm getting:
Cannot override mutable property with read-only property 'testTitle'
Could you help me understanding what's going on? Maybe it's trivial for some people but not for me.
Thanks for your help.
You cannot implement a subclass to be more restrictive than the base class (it would only work the other way round). So if the base class implements a read/write property, you cannot make it read only in your derived class.
Therefore:
final class TestViewController: MyViewController {
override var testTitle: String? { // No error occurs here
get {
return "Test"
}
set {
super.testTitle = newValue
}
}
}
The protocol requires that the adopting class implements a property testTitle with a getter but it does not forbid to declare the property with getter and setter.
To override a property you have to override the (entire) signature in the class, not the protocol requirement.
As testTitle is declared as read/write you cannot override it as read-only.