enum of non-literal values in Swift

Question

Is there any way to map a non-literal value like tuple of dictionary to enums? Following code will throw Raw value for enum must be literal.

enum FileType {
    case VIDEO = ["name": "Video", "contentTypeMatcher": "video/"]
    case IMAGE = ["name": "Image", "contentTypeMatcher": "image/"]
    case AUDIO = ["name": "Audio", "contentTypeMatcher": "aduio/"]
    case PDF   = ["name": "PDF", "contentTypeMatcher":"application/pdf"]
    case TEXT  = ["name": "Text", "contentTypeMatcher": "text/"]
    case FOLDER= ["name": "Folder", "contentTypeMatcher" :"application/x-directory"]
    case PLAIN = ["name": "Plain", "contentTypeMatcher": ""]
}

It's the same when I use tuples:

enum FileType {
    case VIDEO  = (name: "Video", contentTypeMatcher: "video/")
    case IMAGE  = (name: "Image", contentTypeMatcher: "image/")
    case AUDIO  = (name: "Audio", contentTypeMatcher: "aduio/")
    case PDF    = (name: "PDF", contentTypeMatcher:"application/pdf")
    case TEXT   = (name: "Text", contentTypeMatcher: "text/")
    case FOLDER = (name: "Folder", contentTypeMatcher :"application/x-directory")
    case PLAIN  = (name: "Plain", contentTypeMatcher: "")
}

Answer 1

@Antonio gives workaround but does not answer the actual question.

Define your enum.

enum FileType {

    case Image, Video
}

Give cases non-literal values, whatever type you want with conforming to RawRepresentable protocol. Do it by enum extension to have cleaner code.

extension FileType: RawRepresentable {

    typealias Tuple = (name: String, contentTypeMatcher: String)

    private static let allCases = [FileType.Image, .Video]

    // MARK: RawRepresentable

    typealias RawValue = Tuple

    init?(rawValue: Tuple) {

        guard let c = { () -> FileType? in

            for iCase in FileType.allCases {
                if rawValue == iCase.rawValue {
                    return iCase
                }
            }
            return nil

        }() else { return nil }
        self = c
    }

    var rawValue: Tuple {

        switch self {
        case .Image: return Tuple("Image", "image/")
        case .Video: return Tuple("Video", "video/")
        }
    }
}

To be able to match Tuple in switch, implement pattern matching operator.

private func ~= (lhs: FileType.Tuple, rhs: FileType.Tuple) -> Bool {

    return lhs.contentTypeMatcher == rhs.contentTypeMatcher && lhs.name == rhs.name
}

And thats it...

let a = FileType.Image
print(a.rawValue.name) // "Image"
let b = FileType(rawValue: a.rawValue)!
print(a == b) // "true"
print(b.rawValue.contentTypeMatcher) // "image/"

Let's say I answered the question without questioning. Now... Enums (in Swift at least) are designed to have unique cases. Caveat to this workaround is that you can (I hope by accident) hold same rawValue for more cases. Generally your example code smells to me. Unless you (for very reasonable reason) need to create new enum value from tuple, consider redesign. If you want go with this workaround, I suggest (depends on project) to implement some check if all case raw values are unique. If not, consider this:

enum FileType {

    case Video, Image

    var name: String {
        switch self {
        case .Image: return "Image"
        case .Video: return "Video"
    }

    var contentTypeMatcher: String {
        switch self {
        case .Image: return "image/"
        case .Video: return "video/"
    }
}

Answer 2

The language reference, when talking about Enumeration Declaration, clearly states that:

the raw-value type must conform to the Equatable protocol and one of the following literal-convertible protocols: IntegerLiteralConvertible for integer literals, FloatingPointLiteralConvertible for floating-point literals, StringLiteralConvertible for string literals that contain any number of characters, and ExtendedGraphemeClusterLiteralConvertible for string literals that contain only a single character.

So nothing else but literals can be used as raw values.

A possible workaround is to represent the dictionary as a string - for example, you can separate elements with commas, and key from value with colon:

enum FileType : String {
    case VIDEO = "name:Video,contentTypeMatcher:video/"
    case IMAGE = "name:Image,contentTypeMatcher:image/"
    ...
}

Then, using a computed property (or a method if you prefer), reconstruct the dictionary:

var dictValue: [String : String] {
    var dict = [String : String]()

    var elements = self.rawValue.componentsSeparatedByString(",")
    for element in elements {
        var parts = element.componentsSeparatedByString(":")
        if parts.count == 2 {
            dict[parts[0]] = parts[1]
        }
    }

    return dict
}