swift protocol conformance when same property name is optional - swift

Question

When a protocol declares a property as optional and a concrete type declares it as non-optional, how can I make the concrete type conform to the protocol?
Here's the problem:
protocol Track {
var trackNumber: Int? { get } // not all tracks have a track number
}
struct SpotifyTrack {
let trackNumber: Int // all SpotifyTrack are guaranteed to have a track number
}
extension SpotifyTrack: Track {
var trackNumber: Int? {
return self.trackNumber // WARNING: All paths through this function will call itself
}
}
I don't want to make trackNumber optional in SpotifyTrack because I know the value will always be there for SpotifyTracks. Are there are any solutions more elegant than just renaming the properties?

Answer 1

There is no elegant solution to your problem other than renaming the conflicting property on the conforming type.
Swift doesn't allow 2 properties of the same name to exist on a type even if their types are different. On the other hand, Int? and Int are completely different types, so you cannot have trackNumber: Int fulfil the protocol requirement of trackNumber: Int?.
The only solution (other than changing the type in either the protocol or the struct) is to rename the non-Optional property in SpotifyTrack and make an optional computed property of the same name returning the non-optional one.
protocol Track {
var trackNumber: Int? { get }
}
struct SpotifyTrack {
private let _trackNumber: Int
}
extension SpotifyTrack: Track {
var trackNumber: Int? { _trackNumber }
}

Answer 2

One way could be that you have a base track protocol and then have a second protocol which extend the base protocol. For example
protocol BaseTrackProtocol {
var title:String
var artist:String
}
protocol SpotifyTrackProtocol : BaseTrackProtocol {
var trackNumber:Int
}
struct SoptifyTrack: SpotifyTrackProtocol {
var title:String
var artist:String
var trackNumber:Int
}
other type of tracks could then follow different extensions of the base track protocol
hope it helps :)

Answer 3

You can have a second property that acts as backing for the first:
protocol Track {
var trackNumber: Int? { get }
}
struct SpotifyTrack {
var realTrackNumber: Int
}
extension SpotifyTrack: Track {
var trackNumber: Int? { self.realTrackNumber }
}
However, I have a feeling that that is what you mean by "renaming": you would prefer not to do that. Nevertheless, the "instructions" of a protocol are firm: you cannot adopt Track without declaring a trackNumber that is explicitly typed as Int?.
Objective-C has #optional protocol members, meaning you could have Track declare trackNumber Int but #optional, and then you could adopt Track without having a trackNumber at all. But if you wanted to take advantage of that, this could not be a struct.