struct User: Codable {
  let firstName: String
  let lastName: String?

  private enum CodingKeys: CodingKey {
    case firstName
    case lastName
  }

  init(from decoder: any Decoder) throws {
    let container: KeyedDecodingContainer<User.CodingKeys> = try decoder.container(keyedBy: User.CodingKeys.self)

    self.firstName = try container.decode(String.self, forKey: User.CodingKeys.firstName)
    self.lastName = try container.decodeIfPresent(String.self, forKey: User.CodingKeys.lastName)

  }

  func encode(to encoder: any Encoder) throws {
    var container = encoder.container(keyedBy: User.CodingKeys.self)

    try container.encode(self.firstName, forKey: User.CodingKeys.firstName)
    try container.encodeIfPresent(self.lastName, forKey: User.CodingKeys.lastName)
  }
}

struct User_D: Decodable {
  let firstName: String
  let lastName: String?
}

struct User_E: Encodable {
  let firstName: String
  let lastName: String?
}