swift - 覆盖在 Swift 的父类(super class)扩展中声明的类变量

Question

这是 Swift 5.0.1 或 Xcode 的错误吗？

这是在 Xcode 10.2.1 的 Playground 上。

代码是:

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)

playground 没有为 MyUIColor 类指示任何错误

输出是:

UIExtendedSRGBColorSpace 1 0.894 0.541 0.9

libc++abi.dylib:以 NSException 类型的未捕获异常终止

运行时错误说:

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

问题不是类变量重写，而是 self.init 和 super.init 的不当使用。您应该按如下方式更改代码:

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)