Swift enum raw value: not working with CGFloat = -1.0

问题

What does this not work?

enum Aspect : CGFloat {
    case Clockwise = 1.0
    case Anticlockwise = -1.0
}

On Anticlockwise line I'm told that 'raw value for enum case must be a literal'

回答1:

That sounds like a bug. However it seems to work if you omit the decimal part:

enum Aspect : CGFloat {
    case Clockwise = 1
    case Anticlockwise = -1
}

回答2:

The weird thing is that a float with a minus is not a literal, but an expression. So the error message is correct.

From the Swift programming language:

Unlike with integer literals, negative floating-point numbers are expressed by applying the unary minus operator (-) to a floating-point literal, as in -42.0. The result is an expression, not a floating-point literal.

回答3:

This has been fixed in Swift 1.2 (Xcode 6.3 beta). From the release notes:

Negative floating-point literals are now accepted as raw values in enums.

So your code now compiles and works without problems, and you can now also define non-integral negative enumeration values, which was not possible before:

enum Aspect : CGFloat {
    case Clockwise = 1.0
    case Anticlockwise = -1.0
    case Strange = -1.25
}

来源：https://stackoverflow.com/questions/27044476/swift-enum-raw-value-not-working-with-cgfloat-1-0