Tell Me Quando - Implementing Feature Flags
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Feature flags allow software developers to experiment with new features or changes by hiding or exposing functionality while the software is in development. The document discusses implementing feature flags by using build configurations and conditional compilation to produce different versions from the same codebase. It provides examples of using feature flags for minor UI changes like changing colors or text, and major UI changes like using different views. Tests should test both the original code with feature flags disabled and new code with them enabled.
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Developer Hub:
https://developer.mongodb.com
YouTube Channel:
https://www.youtube.com/mongodb
Podcast:
https://www.mongodb.com/podcast
https://linktr.ee/unicodeu00d1
Twitter [Me]:
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Tell Me Quando - Implementing Feature Flags
- 1. Jorge D. Ortiz Fuentes Mobile Developer Advocate, MongoDB WELCOME Implementing Feature Flags Tell Me Quando
- 2. Agenda What are Feature Flags? Why using Feature Flags? Implementing Feature Flags Three Common Scenarios Recap
- 3. What are Feature Flags? Why using them?
- 4. A set of constants that hide or expose functionality while it is on development
- 5. It is all about features Feature: a characteristic of your product (has/is) User Story: a feature from the perspective of the end-user Display list of items Receive notifications about data changes Add a new item to the list Persist data locally New look and feel Sync with other devices Animations and eye-candy …
- 6. New Feature
- 7. Let s Code Then! git branch
- 8. No! 🙅
- 9. It is all about branching Git Flow: • Main, develop, feature, release, hot-fix… • Long-lived branches • Feature code reviews GitHub Flow: • Main & feature branches • Long-lived branches still possible • Feature code reviews (Scaled) Trunk-Based Development: • Trunk/main, releases • Daily/very frequent • Smaller code reviews (WIP)
- 10. Why not JUST Coding? Features need time and most likely several steps to complete adding the required code Fixes might be needed while developing the feature Some features get discarded after being implemented Even if they get accepted, they may require • Some process and • Waiting for the next version You need to address your different target audiences: your tests, QA, beta tester production
- 11. One Codebase to Rule them all
- 13. Make Simple Things Simple #if THIS_ENABLED { // New code #else // Previous behavior implementation, if any #endif
- 14. Put the logic in the code Different configuration ≠ Feature flags Use booleans instead of configuration
- 15. But where do I set those flags?
- 16. Requirements for the Flag Variables • Produce different builds for the different audiences from the same codebase • A feature starts being developed in alpha and it is disabled for any other build • It is enabled for the next stage when the previous stage is completed
- 17. Building with Xcode List of files (code & resources) to generate a product Target A set of settings applied to targets Build Configurations Defines actions combining target and configuration Scheme SWIFT_ACTIVE_COMPILATION_CONDITIONS
- 18. Evolution of a Feature Flag Release Beta QA Alpha Release Debug ❌ ✅ ❌ ❌ Development Clean up ➖ Internal test ✅ ❌ ❌ ✅ External test ✅ ❌ ✅ ✅ Release ✅ ✅ ✅ ✅ ➖ ➖ ➖
- 19. Xcode Trickery Don’t use targets to have different files for the flags Use build configurations for each development stage Use xcconfig files for each stage, to enable the flags and use include for other settings Configurations can be tuned exposing $(CONFIGURATION) in Info.plist Use Product Bundle Identifier if you want more than one version running on the same device
- 21. Static vs Dynamic Static • Removes unused code • Fully controlled by development • Defined in the project Dynamic • All code paths are in the binary • Behavior can be changed without rebuilding • Controlled from elsewhere
- 23. Three Common Scenarios Change some logic or how a layer is implemented Logic or layer impl. Change color, text, position, but keep the “same” UI structure Minor View Change Increase or reduce the number of views used to interact with the user Mayor View Change
- 24. Let s Code Together CODE REPOSITORY AVAILABLE LATER
- 26. Minor UI Change struct MoodButton: View { let mood: Mood var body: some View { Text(String("(mood)")) .font(Font.system(size: 40)) .padding() #if NEW_UI .background(Color.red) #else .background(Color.accentColor) #endif .cornerRadius(10) } }
- 27. Major UI Change @main struct MoodLoggerApp: App { var body: some Scene { WindowGroup { NavigationView { #if NEW_UI NewEntriesListView(viewModel: NewEntriesListViewModel(repository: InMemoryEntryRepository())) #else EntriesListView(viewModel: EntriesListViewModel(repository: InMemoryEntryRepository())) #endif } } } }
- 28. Do I Need to have Tests in Place? No! You don’t need to But it does help a lot Love your future self and your team HINT
- 29. How do the tests change? Test your old code: feature flag disabled Test your new code: feature flag enabled
- 30. Recap
- 31. Summary Feature flags allow to be agile • Evolve your code without causing disruptions • Change priorities on the fly • Tune up deployment Implementation is easy • Build configurations • xcconfig for each of the configuration • If expression to choose between old and new implementation Use feature flags not just for domain logic, but alternative implementations, and different UIs
- 32. Thank you!
- 33. Q&A
- 34. Resources Developer Hub: https://developer.mongodb.com YouTube Channel: https://www.youtube.com/mongodb Podcast: https://www.mongodb.com/podcast https://linktr.ee/unicodeu00d1 Twitter [Me]: https://www.twitter.com/jdortiz