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

[Jordan Rose]

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 <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.
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