Check protocol conformance when protocol contains an enum in Swift?

Question

In Swift, in order to check protocol conformance with is or as? downcasting you must mark the protocol with the @objc attribute. Once you mark a protocol with that attribute it seems you can not have a protocol with an enum as a property because enums cannot be represented in Objective-C.

enum Language:String {
    case English = "English"
    case Spanish = "Spanish"
    case German = "German"
}

@objc protocol Humanizable {
    var language:Language { get set }
}

You'll get an error: error: property cannot be marked @objc because its type cannot be represented in Objective-C

Here is full example: http://swiftstub.com/475659213/

In the example if you change the Language to String then it works fine.

Thanks for the swiftstub.com link, very useful! An interesting problem too. — user887210
@Graff No prob. At least you can try it out and see the issue I am facing. — Johnston
Yep, I see it. I fooled around a bit but haven't come up with anything yet. Hopefully there's a good answer out there, the most I could come up with was using an Int or String in place of the enum. — user887210

ColinE ColinE · Accepted Answer · 2014-09-15T20:35:22

This is not an answer, but I did spot a compile error in your 'swift stub', Human should be defined as follows:

class Human:Humanizable {
  var name:String = "Frank"
  var language:Language = .English
}

You were trying to create an enum instance from a string literal.

I am a little surprised that protocol conformance checking requires @obj - that's just ugly!

Check protocol conformance when protocol contains an enum in Swift?

1 Answers