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

[Kevin Ballard]

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