Overriding properties in swift

Question

For example a have a first class

public class MyBaseButton: UIButton {      public var weight: Double = 1.0      public var text: String? {         get {             return self.titleForState(.Normal)         }         set {             return self.setTitle(newValue, forState: .Normal)         }     } } 

And inherited class:

public class SomeButton: SomeBaseButton {      override public var text: String? = "text"     override public var weight: Double = 2.0 } 

So, the logic is that SomeClass define own text and weight. But I'm getting an errors:

For text: "Cannot override with a stored property 'text'"

For weight: "Cannot override with a stored property 'weight'"

Answer 1

Interestingly this works just fine in pure Swift classes. For example, this works as expected:

public class FooButton {     public var weight: Double = 1.0 }  public class BarButton: FooButton {     override public var weight: Double = 2.0 } 

The reason it does not work for you is because you are working with Objective-C classes: since UIButton is an Objective-C class, all its subclasses will be too. Because of that, the rules seem to be a bit different.

Xcode 6.3 is actually a bit more informative. It shows the following two errors:

Getter for "weight" overrides Objective-C method "weight" from superclass "FooButton" Setter for "weight" overrides Objective-C method "setWeight:" from superclass "Foobutton"

Since the following does work ...

public class BarButton: FooButton {     override public var weight: Double {         get {             return 2.0         }         set {             // Do Nothing         }     } } 

... my guess is that these methods are simply not synthesized correctly.

I wonder if this is a compiler bug. Or a shortcoming. Because I think it could handle the case.

Maybe the Swift designers thought that in case of overriding weight you could also simply set it to a different value in your initializer. Hm.

Answer 2

In addition, if someone wants to override property to have dynamic effect, see KVO

class MyClass: NSObject {     var date = NSDate() }  class MyChildClass: MyClass {     dynamic override var date: NSDate {         get { return super.date }         set { super.date = newValue }     } }