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Setting Boundaries

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Francisco Díaz @fco_diaz

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3 iOS Devs 28 hours 1 project == Merge Conflicts

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What do we want? → Minimize duplication of code. → Develop independently without stepping on each other's toes.

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Feature verticals: → Big Panic button → Today widget → Knock

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Big Panic button:

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What needs to be done? → Create the button. → We need a way to create reports. → Make a backend call to save this information.

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Today widget:

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What needs to be done? → Create the extension button. → We need a way to create reports. → Make a backend call to save this information.

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What was it that we wanted? → Minimize duplication of code. → Develop independently without stepping on each other's toes.

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Let's try again!

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→ Create the button. → We need a way to create reports. → Make a backend call to save this information.

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UI / Presentation Create the button.

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Business logic We need a way to create reports.

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Backend connection Make a backend call to save this information.

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To recap: → Minimize duplication of code. → Develop independently without stepping on each other's toes.

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We can solve any problem by introducing an extra level of indirection — David Wheeler

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Dependency inversion

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struct ModelDataManager { let APIClient: APIType init(APIClient: APIType) { self.APIClient = APIClient } }

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protocol APIType { func createReport(completion: JSONDictionary? -> Void) } struct API { private let manager: Alamofire.Manager init() { manager = Alamofire.Manager() } } extension API: APIType { func createReport(completion: JSONDictionary? -> Void) { manager.request(.POST, "https://some.com/api/report") .responseJSON { response in completion(response) } } }

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struct ModelDataManager { let APIClient: APIType init(API: APIType) { self.APIClient = API } static func defaultManager() -> ModelDataManager { let APIClient = API() return ModelDataManager(API: APIClient) } func createReport(completionHandler completion: Report? -> Void) { APIClient.createReport() { jsonDictionary in let report = ... // Parse jsonDictionary into Report completion(report) } } }

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Benefits → Testable. → Decoupled. → Easy to fake our networking layer.

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struct FakeAPI: APIType { func createReport(completion: JSONDictionary? -> Void) { let dictionary = ["id": 12345] completion(dictionary) } }

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struct ModelDataManager { let APIClient: APIType init(API: APIType) { self.APIClient = API } static func defaultManager() -> ModelDataManager { // let APIClient = API() let APIClient = FakeAPI() return ModelDataManager(API: APIClient) } }

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Questions? Slides are available at: https://github.com/fdiaz/settings-boundaries-talk References: Architecture: The Lost Years The Clean Architecture