medium-codable-dynamic-type.swift

struct AnimalContainer: Decodable {
  let animal: Animal

  enum AnimalType: String, Decodable {
    case cat
    case dog
  }

  enum CodingKeys: String, CodingKey {
    case type
  }

  init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    let animalType = try container.decode(AnimalType.self, forKey: .type)

    switch animalType {
    case .cat:
      self.animal = try Cat(from: decoder)
    case .dog:
      self.animal = try Dog(from: decoder)
    }
  }
}

// Usage example
let animals = try JSONDecoder()
  .decode([AnimalContainer].self, from: exampleData)
  .map { $0.animal }
print(animals) // [Cat name: Kitty, Dog name: Doggy]