Playing around with enums and computed properties as a way to display formatted values in Swift. Usage: `let sek = Currency.Code(rawValue: "SEK"); print(sek.display("42.50")`

currencyDisplayAsEnum.swift

class Currency {

  static private let decimals: [Code: Int] = [
    Code.None: 0,
    Code.DKK: 2,
    Code.GBP: 2,
    Code.NOK: 2,
    Code.SEK: 2,
    Code.USD: 2,
    Code.XBT: 2
  ]
  
  static private let formatStrings: [Code: String] = [
    Code.None: "%@ Rupees",
    Code.DKK: "%@ DKK",
    Code.GBP: "%@ GBP",
    Code.NOK: "%@ NOK",
    Code.SEK: "%@ SEK",
    Code.USD: "$%@",
    Code.XBT: "%@ XBT"
  ]
  static private var formatters: [Code: NSNumberFormatter] = [
    Code.None: NSNumberFormatter()
  ]
  static private func makeFormatter(code: Code) -> NSNumberFormatter {
    let d = decimals[code]!
    // ensure decimals max length
    let nf = NSNumberFormatter()
    nf.numberStyle = NSNumberFormatterStyle.DecimalStyle
    nf.minimumFractionDigits = 0 // strip trailing zeros
    nf.maximumFractionDigits = d
    return nf
  }
  
  enum Code: String, CustomStringConvertible {
    case None = "_"
    case DKK  = "DKK" // Danish krone
    case GBP  = "GBP" // Pound sterling
    case NOK  = "NOK" // Norwegian krone
    case SEK  = "SEK" // Swedish krona/kronor
    case USD  = "USD" // United States dollar
    case XBT  = "XBT" // Bitcoin
    var description:  String { return self.rawValue }
    var formatString: String { return formatStrings[self]! }
    // Manually implement a lazy getter, since enums can't store properties
    var formatter: NSNumberFormatter {
      if let nf = formatters[self] {
        return nf
      } else {
        let nf = NSNumberFormatter()
        formatters[self] = nf
        return nf
      }
    }
    func display(amount: NSDecimalNumber) -> String {
      let strAmount = self.formatter.stringFromNumber(amount)
      return String(format: self.formatString, strAmount)
    }
  }
  
  func tryIt() {
    let sekCurrency = Code(rawValue: "SEK")!
    print(sekCurrency.display("42.50"))
  }
}