a.swift

// WARNING: Does not compile
extension Storage {
  func save(object: Any, forKey: String) {
    switch object {
    case let image as Image:
      let data = UIImagePNGRepresentation(image)
    case let object as Codable:
      let encoder = JSONEncoder()
      try? encoder.encode(object) // Cannot invoke 'encode' with an argument list of type '(Codable)'
    default:
      break
    }
  }
}

storage.save(15, forKey: "number")
storage.save(image, forKey: "image")