[swift-evolution] Discussion: Enforce usage of @available on enum cases

[Stuart Breckenridge]

I'll put together a draft in a new thread. 

Sent from my iPhone

> On 26 May 2016, at 13:37, Charlie Monroe <charlie at charliemonroe.net> wrote:
> 
> Personally, I'd support splitting the @available attribute into:
> 
> @available - indicating that the identifier is available since some version.
> @unavailable - indicating that it's unavailable for certain.
> @deprecated - indicating deprecation.
> 
> +
> 
> @restricted as Stuart suggests, which seems very useful.
> 
> @available (iOS, unavailable, message="Not available on iOS.")
> 
> vs.
> 
> @unavailable (iOS, message="Not available on iOS.")
> 
> 
> IMHO removes some unnecessary boilerplate.
> 
> Charlie
> 
>> On May 26, 2016, at 6:36 AM, Stuart Breckenridge via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> Taking the long form approach:
>> 
>> enum Things:String {
>>     @available (iOS 9.0, tvOS 9.0, watchOS 2.0, *)
>>     @available (OSX, unavailable, message="Not available on OS X.")
>>     case MobileThing = "com.example.mobile"
>>     
>>     @available (iOS, unavailable, message="Not available on iOS.")
>>     @available (tvOS, unavailable, message="Not available on tvOS.")
>>     @available (watchOS, unavailable, message="Not available on watchOS.")
>>     @available (OSX 10.11, *)
>>     case DesktopThing = "com.example.desktop"
>> }
>> 
>> This yields the expected result in a tvOS app:
>> 
>> func that(thing:Things) -> () {
>>         print(thing)
>> }
>> that(.DesktopThing) // 'DesktopThing' is unavailable. Not available on tvOS.
>> 
>> A limited availability attribute does have some merit, perhaps using a different keyword (so you know you are choosing it), for example:
>> 
>>     	@restricted (OSX 10.11, *, message="Only available on OS X.")
>>     	case DesktopThing = "com.example.desktop"
>> 	
>> 	func that(thing:Things) -> () {
>>         	print(thing)
>> 	}
>> 	that(.DesktopThing) // 'DesktopThing' is unavailable. Only available on OS X.
>> 
>> 
>> ...but this is outside the scope of the original topic.
>> 
>> Stuart
>> 
>> 
>>> On 26 May 2016, at 11:23, Jordan Rose <jordan_rose at apple.com> wrote:
>>> 
>>> This was deliberate, and came from the pain of bringing up tvOS (and watchOS). Clang actually had a hack to treat “available on iOS” as “available on tvOS” for a while because of this. When you port something to a new platform, presumably everything that’s been introduced so far should be available from the start.
>>> 
>>> If we introduced a limited availability attribute, I think we’d want to make it more verbose than the normal one, so that you know you’re choosing it.
>>> 
>>> Jordan
>>> 
>>> 
>>>> On May 25, 2016, at 20:18, Jacob Bandes-Storch <jtbandes at gmail.com> wrote:
>>>> 
>>>> Was this an intentional choice, or is it just a temporary limitation? Would a proposal to allow something like "@available(OS X 10.11)" be welcomed?
>>>> 
>>>> 
>>>>> On Wed, May 25, 2016 at 8:17 PM, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
>>>>> The “*” in @available means “all other platforms”. If you want to mark something unavailable on a particular platform, you’ll have to use the long form of the @available attribute. There’s currently no way to mark something “only available on these platforms”.
>>>>> 
>>>>> Jordan
>>>>> 
>>>>>> On May 25, 2016, at 18:48, Stuart Breckenridge via swift-evolution <swift-evolution at swift.org> wrote:
>>>>>> 
>>>>>> Presently, you can mark enum cases as @available but it has no impact. Take the following example:
>>>>>> 
>>>>>> enum Things:String {
>>>>>> 	@available (iOS 9.3, *) case MobileThing = "com.example.mobilething"
>>>>>> 	@available (OSX 10.11, *) case DesktopThing = "com.example.desktopthing"
>>>>>> }
>>>>>> 
>>>>>> Despite the above compiling, the following code will run iOS with no warnings:
>>>>>> 
>>>>>> func takesA(thing:Things) {
>>>>>> 	print(thing)
>>>>>> }
>>>>>> 
>>>>>> takesA(.DesktopThing)
>>>>>> 
>>>>>> 
>>>>>> Are there enough compelling use-cases for @available on enum cases to be considered? At the very least, if @available doesn't do anything on cases, it shouldn't be permitted.
>>>>>> _______________________________________________
>>>>>> swift-evolution mailing list
>>>>>> swift-evolution at swift.org
>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>> 
>>>>> 
>>>>> _______________________________________________
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>> 
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> 
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