Copying ENUM hash and raw values into a dictionary

Question

Is there any way to copy all the values of an enumeration into a dictionary without polling them in any FOR loop?

For example, from this enumeration:

enum FruitPriority: String {
    case PEARS
    case ORANGES
    case APPLES
}

to call some single function from within the ENUM, something like this:

var fruitPriorityArray: [String : Int] = FruitPriority.someFunction()

and get this result (sorted according to hash value):

["PEARS": 0, "ORANGES": 1, "APPLES": 2]

The preference would be to make only a single call to the ENUM.

Thank you.

An “associative array” is called *dictionary* in Swift. A dictionary is an *unordered* collection of key/value pairs. — Martin R, Dec 01 '18 at 14:06
@MartinR Thank you for your prompt answer. You're right. So, would it be possible to accomplish this *unordered?* — iSofia, Dec 01 '18 at 14:08
Why would you need it like that? Why not just change the raw value to an `Int` and use the raw value instead? — Rakesha Shastri, Dec 01 '18 at 14:09

Vyacheslav · Accepted Answer · 2018-12-01T14:36:24.197

2

enum FruitPriority: String, CaseIterable {
    case PEARS
    case ORANGES
    case APPLES
}

let result = FruitPriority.allCases.enumerated().reduce([String: Int]()) { dict, fruit in
    var dict = dict
    dict[fruit.element.rawValue] = fruit.offset
    return dict
}

print(result)

The result is:

["PEARS": 0, "ORANGES": 1, "APPLES": 2]

For version Swift 4.1 and earlier the implementation of CaseIterable:

#if swift(>=4.2)
#else
public protocol CaseIterable {
    associatedtype AllCases: Collection where AllCases.Element == Self
    static var allCases: AllCases { get }
}
extension CaseIterable where Self: Hashable {
    static var allCases: [Self] {
        return [Self](AnySequence { () -> AnyIterator<Self> in
            var raw = 0
            return AnyIterator {
                let current = withUnsafeBytes(of: &raw) { $0.load(as: Self.self) }
                guard current.hashValue == raw else {
                    return nil
                }
                raw += 1
                return current
            }
        })
    }
}
#endif

Original post of CaseIterable implementation.

edited Dec 01 '18 at 14:36

answered Dec 01 '18 at 14:07

Vyacheslav

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Thank you. But I'm sorry that I didn't mention that I'm not able to use Swift 4.2, as my dev machine is stuck on High Sierra. Xcode 10 requires Mojave. Could this be done without ***CaseIterable***? – iSofia Dec 01 '18 at 14:10
@iSofia You can implement CaseIterable in version earlier – Vyacheslav Dec 01 '18 at 14:11
Really!? I wasn't aware. I'll give it a try. Thanks again Vyacheslav. – iSofia Dec 01 '18 at 14:12
Don't forget to add a link to the original implementation of the CaseIterable implementation, for proper attribution. – Martin R Dec 01 '18 at 14:20
@MartinR I found it several months ago at StackOverflow. Now I've just copied from my own code. I don't really remember the source. But I'll try – Vyacheslav Dec 01 '18 at 14:22
It works! Thank you, Vyacheslav. Especially for the Swift 4.1 workaround. – iSofia Dec 01 '18 at 14:24
I found the original implementation here: https://stackoverflow.com/a/49588446/1630618 – vacawama Dec 01 '18 at 14:32
@vacawama added Thanks. – Vyacheslav Dec 01 '18 at 14:36

Robert Dresler · Answer 2 · 2018-12-01T14:25:58.160

If you need just single call to the enum:

Add CaseIterable to your enum and then just create function getDictionary in enum which returns you dictionary (for each enum case will be rawValue assigned as key and hashValue as value )

enum FruitPriority: String, CaseIterable {

    case PEARS
    case ORANGES
    case APPLES

    func getDictionary() -> [String: Int] {
        var dictionary = [String: Int]()
        FruitPriority.allCases.forEach {
            dictionary[$0.rawValue] = $0.hashValue
        }
        return dictionary
    }

}

then you can just call

var fruitPriorityArray: [String : Int] = FruitPriority.getDictionary()

Note: if you're using earlier versions of Swift you can see this to create CaseIterable protocol

Thank you, Robert Dresler. I'll try to implement the protocol you'd recommended. — iSofia, Dec 01 '18 at 14:28

vacawama · Answer 3 · 2018-12-01T14:29:38.077

1

If you make your enum CaseIterable, you can construct a dictionary using reduce(into:). Since the hashValue can now change from run to run, I would recommend using enumerated() to number the cases in order:

enum FruitPriority: String, CaseIterable {
    case PEARS
    case ORANGES
    case APPLES
}

let result = FruitPriority.allCases.enumerated().reduce(into: [:]) { $0[$1.element.rawValue] = $1.offset }

print(result)

// ["ORANGES": 1, "APPLES": 2, "PEARS": 0]

edited Dec 01 '18 at 14:29

answered Dec 01 '18 at 14:12

vacawama

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Thank you, vacawama, for the tip on ***reduce into.*** I'm trying to implement it as it seems so much simpler. – iSofia Dec 01 '18 at 14:26

Copying ENUM hash and raw values into a dictionary

3 Answers3