[swift-dev] New warning message while switching on an enum

[Robert Widmann]

We’ll warn if that kind of cast is a tautology, right?  That leaves only the dynamic casts, which can’t be assumed exhaustive.

~Robert Widmann

> On May 9, 2017, at 2:13 PM, Jordan Rose <jordan_rose at apple.com> wrote:
> 
> It's neither a variable binding nor an expression pattern, right? It has to be compared against the original type to know whether it's exhaustive or not. (Consider "let error as NSError" in a catch clause, which should be considered exhaustive.)
> 
> Jordan
> 
>> On May 9, 2017, at 11:12, Robert Widmann <devteam.codafi at gmail.com <mailto:devteam.codafi at gmail.com>> wrote:
>> 
>> It’s mine, yep.  It looks like it’s classifying the cast in the first pattern as a variable binding instead of an expression pattern.  I’ll push a fix later.
>> 
>> Thanks!
>> 
>>> On May 9, 2017, at 1:52 PM, Jordan Rose <jordan_rose at apple.com <mailto:jordan_rose at apple.com>> wrote:
>>> 
>>> That looks like a bug to me, since of course the first pattern won't always match. I suspect this is Robert's work on trying to make the exhaustive checks better, https://github.com/apple/swift/pull/8908 <https://github.com/apple/swift/pull/8908>. Thanks for catching this!
>>> 
>>> Jordan
>>> 
>>> 
>>>> On May 9, 2017, at 07:09, Pushkar N Kulkarni via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>>>> 
>>>> Hi there, 
>>>> 
>>>> I see a new warning message for switch statements on enums, like this one: 
>>>> 
>>>> enum Test {
>>>>     case one(Any)
>>>>     case two
>>>> }
>>>> 
>>>> let x: Test = .one("One")
>>>> switch x {
>>>>     case .one(let s as String): print(s)
>>>>     case .one: break
>>>>     case .two: break
>>>> }
>>>> 
>>>> enum.swift:9:10: warning: case is already handled by previous patterns; consider removing it
>>>>     case .one: break 
>>>> 
>>>> 
>>>> I do not see this warning with the 04-24 dev snapshot. 
>>>> 
>>>> The warning goes away with the use of the wildcard pattern in the second case:
>>>> 
>>>> switch x {
>>>>     case .one(let s as String): print(s)
>>>>     case .one(_): break
>>>>     case .two: break
>>>> }
>>>> 
>>>> 
>>>> I am wondering if this change is intentional, though it does make sense to me. Can someone please point me to the related commit?
>>>> 
>>>> Thanks in advance!
>>>> 
>>>> Pushkar N Kulkarni,
>>>> IBM Runtimes
>>>> 
>>>> Simplicity is prerequisite for reliability - Edsger W. Dijkstra
>>>> 
>>>> 
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>>> 
>> 
> 

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