Advanced and Practical Enum usage in Swift

Objective-C Support

released Fri, 01 Mar 2019

Objective-C Support

Integer-based enums such as can be bridged to Objective-c via the @objc attribute:

@objc enum Bit: Int { 

   case zero = 0 

   case one = 1


However once you venture away from integers (say String) or start using associated values you can't use enums from within Objective-C.

There is a manual way though. Add two methods to your enum, define a type replacement on the @objc side, and you can move enums back and forth just fine, without having to conform to private protocols:

enum Trade {

     case buy(stock: String, amount: Int)

     case sell(stock: String, amount: Int)


// This type could also exist in Objective-C code.

@objc class ObjcTrade: NSObject {

     var type: Int

     var stock: String

     var amount: Int

     init(type: Int, stock: String, amount: Int) {

         self.type = type

         self.stock = stock

         self.amount = amount



extension Trade  {

     func toObjc() -> ObjcTrade {

         switch self {

         case let .buy(stock, amount):

             return ObjcTrade(type: 0, stock: stock, amount: amount)

         case let .sell(stock, amount):

             return ObjcTrade(type: 1, stock: stock, amount: amount)



     static func fromObjc(source: ObjcTrade) -> Trade? {

         switch (source.type) {

         case 0: return source.stock, amount: source.amount)

         case 1: return Trade.sell(stock: source.stock, amount: source.amount)

         default: return nil




This still has the downside that you need to mirror your enum via an NSObject based type on the Objective-C side (or you could just go and use an NSDictionary), but if you ever end up in a situation where you need to access an enum with associated values from Objective-C, this is a way to do it.