Developing modular apps on iOS

Slides from my talk at NSPresenter Madrid on February 28th

Transcript

1. Developing modular apps on iOS NSPresenter Madrid - February 28th @pepibumur 1
2. About me — Production Engineer at Shopify. — Building tools for mobile developers. — Born and raised in the ❤ Murcia. — Suffering the ☔ in Berlin. — # ppinera.es — $ @pepibumur — % pedro.pinera@shopify.com 2
3. What/why/how should I modularize my app? @pepibumur 3
4. What @pepibumur 4
5. "Modularizing an app consists on organising your app code and resources in multiple modules" @pepibumur 5
6. A module can be — A library: If it doesn't have resources. — A framework: If it has them. — Static: If it's linked at compile time. — Dynamic: If it's linked at startup time. @pepibumur 6
7. Static linking - Compilation time Dynamic linking - Startup time @pepibumur 7
8. Dynamic modules need to be copied into the product for dylib to link them @pepibumur 8
9. Static modules not properly linked might lead to duplicated symbols @pepibumur 9
10. Carthage & CocoaPods are two examples of tools that modularise your dependencies Carthage: Dynamic linking CocoaPods: Static & dynamic linking @pepibumur 10
11. Most of apps are usually built and grown as monoliths 1 target with the app source 1 target with the tests (And maybe some extensions) @pepibumur 11
12. Why @pepibumur 12
13. If you are a freelancer You might want to reuse code @pepibumur 13
14. If you have multiple products !⌚# You might want to reuse code (e.g. Shopify has 5 iOS apps) @pepibumur 14
15. If you want to write weakly coupled components You can leverage modules interfaces (internal by default in Swift) @pepibumur 15
16. If you want to speed up your workflow ⏰ And spend less time waiting for the compiler @pepibumur 16
17. The compile time is proportional to the size of the codebase @pepibumur 17
18. But... Apple is improving the Swi! compiler The compiler builds incrementally (only clean builds should take more time) @pepibumur 18
19. — ⌘ + B (10 minutes) — Change code + (⌘ + B) (4 Seconds) — Change something + (⌘ + B) - (Error) — ⌘ + K (I'm sure this helps) — ⌘ + B (10 minutes) @pepibumur 19
20. — 30 developers. — 10 clean builds per day. — 10 minutes per clean build. 1000 hours spent per month 6.25 engineers @pepibumur 20
21. ! Fortunately, there's something you can do to avoid this @pepibumur 21
22. How @pepibumur 22
23. This is just one approach That works in my experience @pepibumur 23
24. Layers Project Downsides @pepibumur 24
25. Before anyone asks... @pepibumur 25
26. Yes, to avoid the hassle of dealing with versioning or git submodules, all the modules in the same repository @pepibumur 26
27. Microfeatures github.com/pepibumur/microfeatures-guidelines @pepibumur 27
28. @pepibumur 28
29. App module Navigation App lifecycle events Dependency injector @pepibumur 29
30. // App import Core class Registry { static let client = Client(url: "https://shopify.com") static let analytics = Tracker(providers: [.firebase]) static let logger = Logger() } @pepibumur 30
31. import Product import Home // Module: App class HomeCoordinator: HomeDelegate { let navigationController: UINavigationController! // HomeDelegate func didSelectProduct(id: String) { let vc = ProductFeature(id: id, client: Registry.client, analytics: Registry.analytics) .viewController navigationController.pushViewController(productViewController) } } @pepibumur 31
32. Features modules Can be product or service features @pepibumur 32
33. import Core // Module: Product public class ProductFeature { public init(id: String, client: Client, analytics: Analytics) { // Initialization } // !! We just expose UIKit classes public var viewController: UIViewController { // Initialization & dependency injection } } @pepibumur 33
34. import Core // Module: BackgroundSync public class BackgroundSyncer { public init(client: Client, store: Store) { /* Init */ } public func sync(completion: @escaping (Error?) -> Void) } // Module: App @UIApplicationMain class AppDelegate: UIResponder, UIApplicationDelegate { func application(_ application: UIApplication, performFetchWithCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) { Registry.backgroundSyncer.sync { error in // Notify completionHandler } } } @pepibumur 34
35. Shared components are extracted into foundation modules @pepibumur 35
36. // Module: Core public class Client: Clienting {} public class Logger: Logging {} public class Store: Storing {} public class SecureStore: SecureStoring {} // Module: CoreTesting public class MockClient: Clienting { public var executeCount: UInt! public var executeRequest: URLRequest! public var executeStub: (Any?, Error?)! } @pepibumur 36
37. import XCTest import Core import CoreTesting // ! @testable import BackgroundSync final class BackgroundSyncerTests: XCTestCase { var client: MockClient! Var store: MockStore! var subject: BackgroundSyncer! override func setUp() { super.setUp() client = MockClient() store = MockStore() subject = BackgroundSyncer(client: client, store: store) } } @pepibumur 37
38. // Module: Testing import XCTest public extension XCTestCase { public func XCTAssertTapa(_ tapa: Tapa, identifier: String? = nil, tolerance: CGFloat = 0, file: StaticString = #file, line: UInt = #line) { // Asserts the quality of the tapa } } @pepibumur 38
39. // Module: UI public class Color {} public class Font {} public class CustomView {} @pepibumur 39
40. @pepibumur 40
41. Examples app Allow developers to try out the features that they build @pepibumur 41
42. 1 Workspace Multiple projects (fewer git conflicts per project) @pepibumur 42
43. There are not so cool features that I didn't mention (until now) @pepibumur 43
44. From the monolith to modules ! @pepibumur 44
45. 1. Extract build se!ings into config files. 2. Extract foundation components/extensions. 3. Build new features in modules. 4. Gradually extract the existing features. ⚠ Extracting is not easy ⚠ @pepibumur 45
46. Maintaining more than one Xcode project @pepibumur 46
47. Tips to ease maintenance 1. Extract settings into .xcconfig files (a reusable single source of truth). 2. Automate the generation of Xcode projects (e.g. using XcodeGen). 3. Just Debug and Release configurations. @pepibumur 47
48. Continuous integration (Usually clean builds) @pepibumur 48
49. Tips to speed up CI builds 1. Enable parallelize builds on your schemes. 2. Selective builds on CI. Modules: - name: Search path: Search/Sources/** build: xcodebuild -workspace Search.xcworkspace -scheme Search dependencies: - Core - name: Core path: Core/Sources/** build: xcodebuild -workspace Core.xcworkspace -scheme Core @pepibumur 49
50. Catalisis (coming soon) — Command line tool. — Generates workspaces and projects for the module you are working on. — Caches modules to save time on CI and locally. — Offers an API to build/test modules. @pepibumur 50
51. # Examples catalisis generate-xcodeproj App catalisis build Core catalisis test Orders @pepibumur 51
52. Conclusions — Do it of you really need it. — (reuse or decouple code, save time) — More independent and productive teams. — Apple is also improving things. — It comes with some costs and lack of tooling (tools are optimized for monoliths) — A transition into modules is tough. @pepibumur 52
53. Thanks! Slides: h!ps://goo.gl/KAC1EJ @pepibumur 53