medium-codable-strategy.swift

struct UserSettings: Codable {
  let someBool: Bool
  let someDate: Date

  enum CodingKeys: String, CodingKey {
    case someBool = "someDifferentKeyBool"
    case someDate = "someDifferentKeyDate"
  }
}

extension JSONDecoder {
  static var snakeCaseISO8601Date: JSONDecoder = {
    let decoder = JSONDecoder()
    decoder.keyDecodingStrategy = .convertFromSnakeCase
    decoder.dateDecodingStrategy = .iso8601
    return decoder
  }()
}

let data = """
{
  "some_different_key_bool": true,
  "some_different_key_date": "2019-02-06T00:35:01Z"
}
""".data(using: .utf8)!

let obj = try JSONDecoder.snakeCaseISO8601Date.decode(UserSettings.self, from: data)
print(obj) // UserSettings(someBool: true, someDate: 2019-02-06 00:35:01 +0000)