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

[Jordan Rose]

I think they'll all be IsPatterns, which means you can look at the CheckedCastKind.

Jordan


> On May 9, 2017, at 13:54, Robert Widmann <devteam.codafi at gmail.com> wrote:
> 
> Is there a catch-all to query for such casts (sorry, I'm away from my computer at the moment).
> 
> ~Robert Widmann
> 
> 2017/05/09 16:40、Jordan Rose <jordan_rose at apple.com <mailto:jordan_rose at apple.com>> のメッセージ:
> 
>> I think any bridging conversion or upcast would count.
>> 
>> enum Foo {
>>   case foo(NSFileManager)
>>   case bar(NSString)
>>   case baz(Int)
>> }
>> func test(x: Foo) {
>>   switch x {
>>   case .foo(let obj as NSObject):
>>     print("totally legal")
>>   case .bar(let obj as String):
>>     print("also cool")
>>   case .baz(let obj as Any):
>>     print("I'm not sure why, but sure")
>>   }
>> }
>> 
>> Jordan
>> 
>>> On May 9, 2017, at 11:29, Robert Widmann <devteam.codafi at gmail.com <mailto:devteam.codafi at gmail.com>> wrote:
>>> 
>>> Right.  I guess I should have asked: Are there any other kinds of patterns we consider exhaustive that have this structure?  
>>> 
>>> ~Robert Widmann
>>> 
>>>> On May 9, 2017, at 2:23 PM, Jordan Rose <jordan_rose at apple.com <mailto:jordan_rose at apple.com>> wrote:
>>>> 
>>>> "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 <mailto: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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