Assign a value to an enum case during initalization in Swift

Question

I'm decoding a JSON API to a struct, with a CodingKey enum in order to map the language key from the response to the name property of the struct:

{
  id: "1",
  english: "United States",
  french: "États Unis",
  spanish: "Estados Unidos"
}

struct Country: Codable, Hashable, Identifiable {
  let id: String
  let name: String
  
  enum CodingKeys : String, CodingKey {
    case id
    case name = "french" 
  }
}

I want to be able to control programmatically the assigned name value in the CodingKeys enum so it'll be based on the user device locale.

// English user
country.name // "United States"

// French user
country.name // "États Unis"

I have the function getUserLocale() that checks for the user's locale and returns the string value of it ( english , french , etc...).
How can I make it run during the enum initalization so it'll assign the locale value to the name property?

Answer 1

Implementing custom decoding should work. Here's an example.

let sampleJSON = """
{
  "id": "1",
  "english": "United States",
  "french": "États Unis",
  "spanish": "Estados Unidos"
}
"""

var userLocale = "english"

struct Country: Decodable, Hashable, Identifiable {
    let id: String
    let name: String

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        id = try values.decode(String.self, forKey: .id)
        name = try values.decode(String.self, forKey: CodingKeys(rawValue: userLocale)!)
    }

    enum CodingKeys : String, CodingKey {
        case id
        case english
        case french
        case spanish
    }
}

let decoder = JSONDecoder()
let country = try decoder.decode(Country.self, from: sampleJSON.data(using: .utf8)!)

debugPrint(country)


userLocale = "french"
let anotherCountry = try decoder.decode(Country.self, from: sampleJSON.data(using: .utf8)!)
debugPrint(anotherCountry)

Answer 2

Regardless of the current language you have to decode the entire JSON anyway.

My suggestion is to add a function to return the localized name.

First create another enum for the supported languages

enum CountryCode : String {
    case en, fr, es
}

struct Country: Codable, Hashable, Identifiable {
  let id: String
  let english, french, spanish : String

  func name(for countryCode: CountryCode) -> String {
      switch countryCode {
          case .en: return english
          case .fr: return french
          case .es: return spanish
      }
  }
}

CountryCode is declared with a raw value to be able to initialize a value from the 2-letter country code.