swiftでenumを文字列に変換する

enum Environment {
    case Production
    case Staging
    case Development
    case Test

    var toString : String! {
        switch self {
        case Environment.Production:
            return "Production"
        case Environment.Staging:
            return "Staging"
        case Environment.Development:
            return "Development"
        case Environment.Test:
            return "Test"
        }
    }
}

上記のようなtoStringを作り

let env = Environment.Development
println("Now Environment is " + env.toString)

のようにできる。
最初から文字列のENUMでよいのなら、String型で指定し、

enum Environment : String {
    case Production = "Production"
    case Staging = "Staging"
    case Development = "Development"
    case Test = "Test"
}

とできる。