[swift-evolution] Proposal: Allow @objc(name) on enum declarations

[Harlan Haskins]

An error seems reasonable here.

Error: Ambiguous Objective-C case name for ‘.Two’.

And then the Fix-It is just to put the second case on a new line and provide the @objc(<#name#>) completion.

> On Dec 10, 2015, at 1:56 AM, Kevin Ballard via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Does it make sense to put @objc(name) on enum cases? Such as
> 
> @objc enum Foo: Int {
>    @objc(kFooOne) case One
>    @objc(kFooTwo) case Two
> }
> 
> The only real problem here is what do we do if you say
> 
> @objc(kFooOne) case One, Two
> 
> Either we just apply it to the One variant and ignore the Two variant, possibly with a warning, or we emit an error.
> 
> -Kevin
> 
> On Wed, Dec 9, 2015, at 06:01 PM, Jordan Rose wrote:
>> 
>>> On Dec 9, 2015, at 15:18, Kevin Ballard via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> Swift allows for placing @objc on an enum that has an Int raw type in order to expose it to Obj-C. But it doesn't currently let you rename the enum when exposing it to Obj-C. This is particularly problematic when exposing a Swift enum that's nested in a struct/class, as the nesting resolves ambiguity in Swift but is not present in Obj-C.
>>> 
>>> Example:
>>> 
>>> import Foundation
>>> 
>>> class Foo: NSObject {
>>>   @objc enum Bar: Int {
>>>       case One, Two
>>>   }
>>> }
>>> 
>>> This generates the following:
>>> 
>>> SWIFT_CLASS("_TtC7unnamed3Foo")
>>> @interface Foo : NSObject
>>> - (nonnull instancetype)init OBJC_DESIGNATED_INITIALIZER;
>>> @end
>>> 
>>> typedef SWIFT_ENUM(NSInteger, Bar) {
>>> BarOne = 0,
>>> BarTwo = 1,
>>> };
>>> 
>>> I'd like to resolve this by saying @objc(FooBar) but that emits an error.
>>> 
>>> I'm also going to submit a separate proposal saying we should change the default naming here so the enum is named FooBar, but these two proposals go hand-in-hand (there are cases where you might want to rename a root-level enum, to add a prefix for disambiguation in Obj-C, or you may want to selectively opt out of the proposed renaming rules by forcing your nested enum to use just its name in Obj-C).
>> 
>> +1 to being able to rename @objc enums. I'm a little surprised we even allow exposing nested types to Objective-C, and am not at all sure the printer is set up to handle that correctly, but the renaming is independently useful.
>> 
>> Jordan
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