Enum with localized string in swift

You can use any StringLiteralConvertible, Equatable type for RawValue type of enum.

So, how about:

import Foundation

struct LocalizedString: StringLiteralConvertible, Equatable {

    let v: String

    init(key: String) {
        self.v = NSLocalizedString(key, comment: "")
    }
    init(localized: String) {
        self.v = localized
    }
    init(stringLiteral value:String) {
        self.init(key: value)
    }
    init(extendedGraphemeClusterLiteral value: String) {
        self.init(key: value)
    }
    init(unicodeScalarLiteral value: String) {
        self.init(key: value)
    }
}

func ==(lhs:LocalizedString, rhs:LocalizedString) -> Bool {
    return lhs.v == rhs.v
}

enum DietWithoutResidueOption: LocalizedString {
    case NoDiet = "NoDiet"
    case ThreeDays = "ThreeDays"
    case FiveDays  = "FiveDays"

    var localizedString: String {
        return self.rawValue.v
    }

    init?(localizedString: String) {
        self.init(rawValue: LocalizedString(localized: localizedString))
    }
}

Using this, you can construct DietWithoutResidueOption by 3 ways:

let option1 = DietWithoutResidueOption.ThreeDays
let option2 = DietWithoutResidueOption(rawValue: "ThreeDays") // as Optional
let option3 = DietWithoutResidueOption(localizedString: "OUI, SUR 3 JOURS")  // as Optional

and extract the localized string with:

let localized = option1.localizedString

this is a late answer, but I just had a chat with Apple Engineers about that topic they recommend to do it that way:

    enum LocalizedStrings {
        case title

        var localized: String {
            switch self {
            case .title:
                return NSLocalizedString("My Title", comment: "My Comment")
            }
        }
    }

In your case the solution would be not much different from the original code:

    enum DietWithoutResidueOption {
        case NoDiet
        case ThreeDays
        case FiveDays

        var localizedString: String {
            switch self {
            case .NoDiet:
                return NSLocalizedString("NoDiet", comment: "Some comment")
            case .ThreeDays:
                return NSLocalizedString("ThreeDays", comment: "Some comment")
            case .FiveDays:
                return NSLocalizedString("FiveDays", comment: "Some comment")
            }
        }

        static func dietWithoutResidueOptionWith(localizedString: String) -> DietWithoutResidueOption {
            switch localizedString {
            case DietWithoutResidueOption.ThreeDays.localizedString:
                return DietWithoutResidueOption.ThreeDays
            case DietWithoutResidueOption.FiveDays.localizedString:
                return DietWithoutResidueOption.FiveDays
            default:
                return DietWithoutResidueOption.NoDiet
            }
        }
    }

The reason is that they don't want you to pass variables into NSLocalizedString(). This has something to do with optimization and parsing the strings. Imagine Xcode generating the localizable.strings file on it's own at some point, but it could not find the strings, because they are passed as variables.

Try this, it's pretty simple and straight forward:

enum ChoicesTitle: String {
    case choice1 = "Choice 1"
    case choice2 = "Choice 2"
    case choice3 = "Choice 3"
    case choice4 = "Choice 4"
    case choice5 = "Choice 5"
    case choice6 = "Choice 6"

    func localizedString() -> String {
        return NSLocalizedString(self.rawValue, comment: "")
    }

    static func getTitleFor(title:ChoicesTitle) -> String {
        return title.localizedString()
    }
}

And you could use it like this:

let stringOfChoice1: String = ChoicesTitle.getTitleFor(title: .choice1)

Hope this works for you