Swift Codable multiple types

You can try

struct Root: Codable {
    let description,id: String
    let group,groupDescription: String?
    let name: String
    let value: MyValue

    enum CodingKeys: String, CodingKey {
        case description = "Description"
        case group = "Group"
        case groupDescription = "GroupDescription"
        case id = "Id"
        case name = "Name"
        case value = "Value"
    }
}

enum MyValue: Codable {
    case string(String)
    case innerItem(InnerItem)

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        if let x = try? container.decode(String.self) {
            self = .string(x)
            return
        }
        if let x = try? container.decode(InnerItem.self) {
            self = .innerItem(x)
            return
        }
        throw DecodingError.typeMismatch(MyValue.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for MyValue"))
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        switch self {
        case .string(let x):
            try container.encode(x)
        case .innerItem(let x):
            try container.encode(x)
        }
    }
}

struct InnerItem: Codable {
    let type, id, name: String

    enum CodingKeys: String, CodingKey {
        case type = "__type"
        case id = "Id"
        case name = "Name"
    }
}

---

do {
  let result = try JSONDecoder().decode([Root].self,from:data)
  print(result)
}
catch {
  print(error)
}

Building on the answer of @Sh_Khan and to answer the question of @Nikhi in the comments (how can you access the values) I like to do add this to the enum declaration:

var innerItemValue: InnerItem? {
    switch self {
    case .innerItem(let ii):
        return ii
    default:
        return nil
    }
}

var stringValue: String? {
    switch self {
    case .string(let s):
        return s
    default:
        return nil
    }
}