Enum associated value confusing - swift

Question

When I try use func obj func, I get the error:
Cannot invoke 'obj' with an argument list of type '(message: (QueueAddable))'
I'm confused with Swift types.
Obj func used to get concrete type for decode.
protocol QueueAddable: Encodable {
var playlistsCollection:String? { get }
var playlists: [String]? { get }
}
struct Playlist: QueueAddable {
var playlistsCollection:String? {
return "id"
}
var playlists: [String]? {
return ["id", "id2"]
}
private enum CodingKeys:String,CodingKey {
case playlistsCollection
case playlists
}
public func encode(to encoder: Encoder) throws {
var values = encoder.container(keyedBy: CodingKeys.self)
try values.encode(playlistsCollection, forKey: Playlist.CodingKeys.playlistsCollection)
try values.encode(playlists, forKey: .playlists)
}
}
func obj<Q>(message: Q) where Q: QueueAddable {
let encoder = JSONEncoder()
let data = try! encoder.encode(message)
}
enum SomeEnum {
case playlist(QueueAddable)
func doSome() throws -> Data {
switch self {
case .playlist(let queueAddable):
let encoder = JSONEncoder()
// Error on the following line:
obj(message: queueAddable)
return Data()
}
}
}
let playlist = Playlist()
let data = try SomeEnum.playlist(playlist).doSome()

Answer 1

I think the problem is that the function expects a type and not a protocol. If you make the enum generic using a type that implements the protocol it will work.
Change the enum's first two lines like this:
enum SomeEnum<Q : QueueAddable> {
case playlist(Q)
I tested in the following playground:
import Foundation
protocol QueueAddable: Encodable {
var playlistsCollection:String? { get }
var playlists: [String]? { get }
}
struct Playlist: QueueAddable {
var playlistsCollection:String? {
return "id"
}
var playlists: [String]? {
return ["id", "id2"]
}
private enum CodingKeys:String,CodingKey {
case playlistsCollection
case playlists
}
public func encode(to encoder: Encoder) throws {
var values = encoder.container(keyedBy: CodingKeys.self)
try values.encode(playlistsCollection, forKey: Playlist.CodingKeys.playlistsCollection)
try values.encode(playlists, forKey: .playlists)
}
}
func obj<Q>(message: Q) where Q: QueueAddable {
let encoder = JSONEncoder()
let data = try! encoder.encode(message)
}
enum SomeEnum<Q : QueueAddable> {
case playlist(Q)
func doSome() throws -> Data {
switch self {
case .playlist(let queueAddable):
let encoder = JSONEncoder()
// No longer error on the following line:
obj(message: queueAddable)
return Data()
}
}
}
let playlist = Playlist()
let data = try SomeEnum.playlist(playlist).doSome()
Hope it helps!