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

[Jordan Rose]

"as NSError" isn't a tautology, though—the original type is 'Error'. Additionally, the presence or absence of a warning shouldn't affect exhaustiveness analysis, which is currently an error when you get it wrong. Warnings are things you can build with and fix later.

Jordan


> On May 9, 2017, at 11:22, Robert Widmann <devteam.codafi at gmail.com> wrote:
> 
> 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 <mailto: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
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> swift-dev mailing list
>>>>> swift-dev at swift.org <mailto:swift-dev at swift.org>
>>>>> https://lists.swift.org/mailman/listinfo/swift-dev <https://lists.swift.org/mailman/listinfo/swift-dev>
>>>> 
>>> 
>> 
> 

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