> On Apr 2, 2017, at 11:17 PM, Daniel Duan via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>> On Apr 2, 2017, at 11:10 PM, Xiaodi Wu <xiaodi...@gmail.com
>> <mailto:xiaodi...@gmail.com>> wrote:
>>
>> This rule cannot hold. You cannot have the shorthand syntax you propose,
>> disallow mixing of shorthand syntax and the longer form, *and* allow `_` to
>> substitute for any pattern without a label.
>>
>> ```
>> enum E {
>> case foo(a: Int, b: Int, c: Int)
>> case foo(a: String, c: String, e: String)
>> }
>>
>> let e = /* instance of E */
>>
>> switch e {
>> case foo(let a, _, _):
>> // what type is `a` here?
>> break
>> default:
>> fatalError()
>> }
>> ```
>
> That seems like straight up ambiguity with or without restriction on the
> label though? This kind of usability problem should and is discouraged by the
> proposed solution.
Let's make it a little more reasonable:
enum Color {
case color(red: CGFloat, green: CGFloat, blue: CGFloat, alpha:
CGFloat)
case color(hue: CGFloat, saturation: CGFloat, value: CGFloat,
alpha: CGFloat)
}
let c: Color = …
switch c {
case .color(_, _, _, let alpha):
…
}
Interestingly, in this example it would probably be appropriate to match both
cases. I wonder if that's true in the general case.
--
Brent Royal-Gordon
Architechies
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