Swift enum as array index

Question

Maybe I misunderstand enums in swift, but in obj-c I was using enums like this (and using a lot):

class SomeObject;

typedef NS_ENUM(NSUInteger, SomeType) {
    Type1 = 0,
    Type2,       // = 1
    Type3,       // = 2
    TypeInvalid  // = 3
};

- (SomeType)getTypeOf(NSArray *a, SomeObject *o) {
    //for (int i = 0; i < a.count; ++i)
    //    if ([a[i] isEqual:o])
    //        return i;
    NUInteger result = [a indexOfObject:o];
    return result == NSNotFound ? TypeInvalid : result;
}

// Also I could use this:
a[Type3] = someObject;

How to do the same in Swift? Am I forced to use constants (let Type1 = 0), like in Java (public static final int Type1 = 0;)?

Rather than looping and calling isEqual:, just use indexOfObject:. — jscs
– jscs, Commented May 6, 2016 at 18:32

GoZoner · Accepted Answer · 2016-05-06 15:19:43Z

6

Simply:

enum SomeType : Int {
  case Type1, Type2, Type3, TypeInvalid
}

The Apple documentation states:

By default, Swift assigns the raw values starting at zero and incrementing by one each time

So you get Type1 with a rawValue of 0. For example:

  1> enum Suit : Int { case Heart, Spade, Diamond, Club }
  2> Suit.Heart.rawValue
$R0: Int = 0
  3> Suit.Club.rawValue
$R1: Int = 3

Note: In your example code, you'll need to replace return i with return SomeType(rawValue: i)! (although I don't quite understand the logic as apparently i is limited by a.count which might not correspond to a SomeType value)

edited May 6, 2016 at 15:19

answered May 6, 2016 at 15:14

GoZoner

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Comments

Community · Accepted Answer · 2017-05-23 12:17:14Z

In addition to Ed Gamble response, you can also set enum values manually:

enum SomeType : Int {
  case Type1 = 1
  case Type2 = 2
  case Type3 = 3
  case TypeInvalid = -1
}

Using Swift enums you are not limited to Int values:

enum SomeType : String {
  case Type1 = "Type 1"
  case Type2 = "Type 2"
  case Type3 = "Type 3"
  case TypeInvalid = "Invalid type"
}

To get the inner value, you call rawValue:

let foo = SomeType.Type2
foo.rawValue // returns "Type 2"

And you can construct enums from values using init(rawValue:) method:

let rawValue = "Type 2"
let foo = SomeType(rawValue: rawValue)

Note that this init returns an optional, because it may not found a valid enum associated to that value. Having a default value makes error handling much easier:

let foo = SomeType(rawValue: rawValue) ?? SomeType.TypeInvalid

?? is the nil coalescing operator. a ?? b unwraps the value of a if is not nil and returns b otherwise. It's equivalent to a != nil ? a! : b. In this case, SomeType(rawValue:) may not match and return nil and will return .TypeInvalid in that case.

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