swift enum is ignoring CodingKeys

Question

I have a some nested swift classes that are automatically decoded from JSON using the Decodable protocol. Everything works except this one enum.

The json data is a capitalised string of either Open or Fulfilled.

If I use this enum, everything decodes perfectly fine:

enum Status: String, Codable {
    case Open, Fulfilled
}

however i'm trying to get the cases to not use capitalized like this:

enum Status: String, Codable {
    
    case open, fulfilled
    
    private enum CodingKeys: String, CodingKey {
        case open       = "Open"
        case fulfilled  = "Fulfilled"
    }
}

This gives me a decoding error saying:

debugDescription: "Cannot initialize Status from invalid String value Open"

Do CodingKeys not work like this for enums?

Do CodingKeys not work like this for enums? Joakim covers what to do here, but to answer this: there is a default Codable implementation for things which are RawRepresentable by each of the "base" Codable types (String, Int, Bool, etc.). The one for String encodes the raw value directly, and CodingKeys are not involved at all — because you get this default implementation, your CodingKeys enum has no influence over the effective behavior. — Itai Ferber
– Itai Ferber, Commented Feb 22, 2023 at 16:54

Joakim Danielson · Accepted Answer · 2023-02-22 14:25:56Z

4

Since the raw value type of your enum is String you can assign the correct strings directly to your enum items

enum Status: String, Codable {
    case open = "Open"
    case fulfilled = "Fulfilled"
}

If you for some reason do not want to do it this way then you need to implement a custom init(from:)

enum Status: String, Codable {
    case open, fulfilled

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let value = try container.decode(String.self)
        switch value {
        case "Open":
            self = .open
        case "Fulfilled":
            self = .fulfilled
        default:
            // throw an error or use fatalError()
        }
    }
}

edited Feb 22, 2023 at 14:25

answered Feb 22, 2023 at 14:19

Joakim Danielson

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1 Comment

Darren Over a year ago

Wow, I never thought to directly assign them 🙈 thanks

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