Feature Enum

Feature.swift

enum Feature<T: Decodable>: Decodable {
    case disabled
    case enabled(configuration: T)

    init(from decoder: Decoder) throws {
        if let _ = try? EmptyObject.init(from: decoder) {
            self = .disabled
            return
        }

        let parsed = try T.init(from: decoder)
        self = .enabled(configuration: parsed)
    }
}

struct EmptyConfiguration: Decodable {}

typealias ToggleFeature = Feature<EmptyConfiguration>

struct EmptyObject: Decodable {

    enum Errors: Error {
        case containsUnexpected(keys: [String])
    }

    init(from decoder: Decoder) throws {
        let stringKeys = try decoder.container(keyedBy: StringCodingKey.self).allKeys
        if !stringKeys.isEmpty {
            throw Errors.containsUnexpected(keys: stringKeys.map { $0.stringValue })
        }
    }

    private struct StringCodingKey: CodingKey {
        var stringValue: String

        init?(stringValue: String) {
            self.stringValue = stringValue
        }

        var intValue: Int?
        init?(intValue: Int) {
            return nil
        }
    }
}

struct AccountsConfig: Decodable {
    var countryCode: String
}

struct FeatureConfig: Decodable {
    var interac: ToggleFeature
    var accounts: Feature<AccountsConfig> 
}


// Example: interac disabled, accounts enabled with configuration
let interacDisabledAccountsEnabled = """
{
    "interac": {},
    "accounts": { "countryCode": "CA" }
}
"""

let config = try JSONDecoder().decode(FeatureConfig.self, from: json.data(using: .utf8)!)
config.interac // disabled
if case .enabled(let accountConfig) = config.accounts {
    accountConfig.countryCode // CA
}