Enums with data in swift

Question

I would like to use java-like enums, where you can have enum instances with custom data. For instance:

enum Country {
    case Moldova(capital: "Chișinău", flagColors: [Color.Blue, Color.Yellow, Color.Red]);
    case Botswana(capital: "Gaborone", flagColors: [Color.Blue, Color.White, Color.Black]);
}

I could later write:

Country.Moldova.capital;

It seems that I can indicate the variables, but not the values, and I can only assign the values when using the enum, not declaring. Which would be the best way to mimic this behaviour?

holex · Accepted Answer · 2014-07-09 09:41:58Z

16

you can do something like this, which may be helpful: (that is a very generic example only)

enum Country : Int {
    case Moldova, Botwana;

    //

    func capital() -> String {
        switch (self) {
        case .Moldova:
            return "Chișinău"
        case .Botwana:
            return "Gaborone"
        default:
            return ""
        }
    }

    //

    func flagColours() -> Array<UIColor> {
        switch (self) {
        case .Moldova:
            return [UIColor.blueColor(), UIColor.yellowColor(), UIColor.redColor()]
        case .Botwana:
            return [UIColor.blueColor(), UIColor.whiteColor(), UIColor.blackColor()]
        default:
            return []
        }
    }

    //

    func all() -> (capital: String, flagColours: Array<UIColor>) {
        return (capital(), flagColours())
    }

    //

    var capitolName: String {
    get {
        return capital()
    }
    }

    //

    var flagColoursArray: Array<UIColor> {
    get {
        return flagColours()
    }
    }

}

then you can access to the details like this:

let country: Country = Country.Botwana

get the capital

that way:

let capital: String = country.capital()

or another:

let capital: String = country.all().capital

or a third one:

let capital: String = country.capitolName

get the flag's colours:

that way:

let flagColours: Array<UIColor> = country.flagColours()

or another:

let flagColours: Array<UIColor> = country.all().flagColours

or a third one:

let flagColours: Array<UIColor> = country.flagColoursArray

edited Jul 9, 2014 at 9:41

answered Jul 9, 2014 at 9:30

holex

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1 Comment

André Fratelli Over a year ago

This is what I ended up doing, although I don't think that it's ideal, it does mimmic the behaviour I was looking for.

Matthew Gharrity · Accepted Answer · 2014-11-02 19:38:26Z

3

Here is another generic example that is similar to the one posted by holex, but a bit closer to how it looks in Java. (I like it because all of the custom data is in one place). Instead of switching on 'self' in separate methods, I simply create a static dictionary that maps each case to a tuple containing the appropriate data. Then, I have convenience var's to get at the data easily.

enum TestEnum {
    case One
    case Two
    case Three

    private static let associatedValues = [
        One:    (int: 1, double: 1.0, string: "One"),
        Two:    (int: 2, double: 2.0, string: "Two"),
        Three:  (int: 3, double: 3.0, string: "Three")
    ]

    var int: Int {
        return TestEnum.associatedValues[self]!.int;
    }

    var double: Double {
        return TestEnum.associatedValues[self]!.double;
    }

    var string: String {
        return TestEnum.associatedValues[self]!.string;
    }
}

You can access the custom data like so:

println(TestEnum.One.int)      // 1
println(TestEnum.Two.double)   // 2.0
println(TestEnum.Three.string) // Three

answered Nov 2, 2014 at 19:38

Matthew Gharrity

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1 Comment

Andres Riofrio Over a year ago

I really like this solution because it keeps each enum data in a single line. Have you figured out how to get the compiler to check that all the cases are covered in associatedValues?

jtbandes · Accepted Answer · 2015-09-17 04:03:57Z

2

Unfortunately it seems like enums with raw values are limited to literal values. You may want to file a bug.

As an alternative, you could do something like this:

let Country = (
    Moldova: (capital: "Chișinău", flagColors: [Color.Blue, Color.Yellow, Color.Red]),
    Botswana: (capital: "Gaborone", flagColors: [Color.Blue, Color.White, Color.Black])
)

or this:

struct Country {
    let capital: String
    let flagColors: [Color]
}

let Countries = (
    Moldova: Country(capital: "Chișinău", flagColors: [.Blue, .Yellow, .Red]),
    Botswana: Country(capital: "Gaborone", flagColors: [.Blue, .White, .Black])
)

edited Sep 17, 2015 at 4:03

answered Jul 9, 2014 at 8:54

jtbandes

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Enums with data in swift

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get the capital

get the flag's colours:

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