How to use Objective-C enum in Swift

Question

I have 2 enum definition in Objective-C file and Swift file.

Japanese.h

typedef enum {
  JapaneseFoodType_Sushi = 1,
  JapaneseFoodType_Tempura = 2,
} JapaneseFoodType;

US.swift

enum USFoodType {
  case HUMBERGER;
  case STEAK;
}

as we know, I can use Objective-C enum like following;

Japanese.m

- (void)method {
  JapaneseFoodType type1 = JapaneseFoodType_Sushi;
  JapaneseFoodType type2 = JapaneseFoodType_Tempura;
  if (type1 == type2) {// this is no problem
  }
}

But I can not use Objective-C enum in Swift file like following;

  func method() {
    var type1: USFoodType = USFoodType.HUMBERGER// no problem
    var type2: USFoodType = USFoodType.HUMBERGER// no problem
    if type1 == type2 {

    }

    var type3: JapaneseFoodType = JapaneseFoodType_Sushi// no problem
    var type4: JapaneseFoodType = JapaneseFoodType_Tempura// no problem
    if type3 == type4 {// 'JapaneseFoodType' is not convertible to 'Selector'

    }
  }

Is this a bug of Swift? And how can I use Objective-C (C) enum in Swift file?

score 78 · Accepted Answer · answered Aug 01 '14 at 10:45

78

I think this is a bug because Swift should define == for C enums or an "to Int" conversion but it doesn't.

The simplest workaround is redefining your C enum as:

typedef NS_ENUM(NSUInteger, JapaneseFoodType) {
    JapaneseFoodType_Sushi = 1,
    JapaneseFoodType_Tempura = 2,
};

which will allow LLVM to process the enum and convert it to a Swift enum (NS_ENUM also improves your Obj-C code!).

Another option is to define the equality using reinterpret hack:

public func ==(lhs: JapaneseFoodType, rhs: JapaneseFoodType) -> Bool {
    var leftValue: UInt32 = reinterpretCast(lhs)
    var rightValue: UInt32 = reinterpretCast(rhs)

    return (leftValue == rightValue)
}

answered Aug 01 '14 at 10:45

Sulthan

128,090
22
218
270

Thank you for your solution! I'll use NS_ENUM to solve this problem (or wait to the apple's bugfix) I didn't know that we can override operator like C++. – Mitsuaki Ishimoto Aug 01 '14 at 11:01
thank you my problem solved. – Ramkumar chintala Aug 01 '16 at 10:37
1

my `Objective C` `enum` is defined with `NS_ENUM`, but still having problem with the call of enum. – Shamsiddin Saidov Apr 14 '17 at 11:08
@Sulthan what is `reinterpretCast`? – Vyachaslav Gerchicov Mar 09 '20 at 09:47
@VyachaslavGerchicov Something that doesn't exist in Swift any more, I guess. This was an answer for Swift 1.x. Nowadays, you would probably use `withMemoryRebound`. – Sulthan Mar 09 '20 at 10:00

score 24 · Answer 2 · answered Aug 01 '14 at 10:44

24

You should use NS_ENUM macro to make your enums Swift-compatible.

Also note that your enum literals should be accessed like JapaneseFoodType._Sushi, so it's probably a good idea to remove the underscore.

answered Aug 01 '14 at 10:44

Nikolay Kasyanov

897
5
14

How to use Objective-C enum in Swift

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