Override class variable declared in the superclass's extension in Swift - swift

Question

Is it a bug of Swift 5.0.1 or Xcode?
This is in the playground with Xcode 10.2.1.
The codes are:
extension UIColor {
#objc class var myGolden: UIColor {
return self.init(red: 1.000, green: 0.894, blue: 0.541, alpha: 0.900)
}
}
print(UIColor.myGolden)
class MyUIColor: UIColor {
override class var myGolden: UIColor {
return super.init(red: 1.000, green: 0.894, blue: 0.541, alpha: 0.750)
}
}
print(MyUIColor.myGolden)
The playground does not indicate any error for the class MyUIColor
The output is:
UIExtendedSRGBColorSpace 1 0.894 0.541 0.9
libc++abi.dylib: terminating with uncaught exception of type NSException
and the runtime error says:
error: Execution was interrupted, reason: signal SIGABRT. The process
has been left at the point where it was interrupted, use "thread
return -x" to return to the state before expression evaluation.

Answer 1

The problem isn't the class variable override, is instead the improper use of self.init and super.init. You should change the code as follows:
extension UIColor {
#objc class var myGolden: UIColor {
return UIColor(red: 1.000, green: 0.894, blue: 0.541, alpha: 0.900)
}
}
print(UIColor.myGolden)
class MyUIColor: UIColor {
override class var myGolden: UIColor {
return UIColor(red: 1.000, green: 0.894, blue: 0.541, alpha: 0.750)
}
}
print(MyUIColor.myGolden)

Answer 2

Changing the self.init and super.init calls to UIColor.init fixes the issue. You should only call self.init and super.init from convenience initialisers or subclass initialisers respectively, when creating an instance of your class in a computed property or any other functions, you should be calling the init methods using the type name rather than self or super.
extension UIColor {
#objc class var myGolden: UIColor {
return UIColor(red: 1.000, green: 0.894, blue: 0.541, alpha: 0.9)
}
}
print(UIColor.myGolden)
class MyUIColor: UIColor {
override class var myGolden: UIColor {
return UIColor(red: 1.000, green: 0.894, blue: 0.541, alpha: 0.75)
}
}
print(MyUIColor.myGolden)