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

[Charlie Monroe]

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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto:swift-evolution at swift.org>
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>> 
>>> 
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>> 
>>> 
>> 
> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160526/d85d0c42/attachment.html>