Rewriting iOS apps in the wild

Rewriting apps is something that we all do at some point. Being able to ship your new code along with the existing one while the app keeps working is a tricky process that can be counterintuitive at some stages.

In this talk we will go through a set of recommendations, techniques and tips that might help you to rewrite your app without going crazy or spending a disproportioned amount of time in the process.

Transcript

1. Rewriting iOS apps in the wild
2. Alberto Gragera alberto@karumi.com Co-Founder and Technical Director @gragera_
3. We embark on every project with a commitment to create something elegant, enduring and effective. That is our heartbeat. Our approach is uniquely simple and honest, we are a small dedicated software studio, delivering outstanding work. Karumi is the Rock Solid code software development studio.
4. OPINIONS
5. I've seen things you people wouldn't believe
6. Refactor vs Rewrite
7. Two things to keep in mind before getting started
8. Reescribir una App es un proceso muy complicado y en cierta medida contraintuitivo con respecto a lo que nos enseñan las buenas prácticas del software Do not underestimate complexity
9. Think twice before rewriting from scratch
10. Why do we have to rewrite?
11. Because shit happens
12. “Ok, I have the time. Let’s do this right!”
13. I can build this cake!
16. Sooooo yeah, rewriting apps is something that we do every now and then ¯\_(ϑ)_/¯
17. Common sense
18. Write the tests before rewriting! Common sense
19. BUT it might come with significant tradeoffs The concept is "
20. If you are rewriting some SpaceX code, you might want to write the tests first, no matter how complex it is We are making mobile apps anyway
21. Replace layers transversally Common sense
22. TONS OF
23. AND DANGER
24. PROCESS
25. Think hard about your new architecture
26. Viper-ish
27. Design your APIs as you would love to use them
28. Use whatever the language offers to make your APIs shine
29. Evaluate how much would it cost to make the old code testable Probably days
30. Some tips that could help you
31. Protocol extensions to wrap existing models
32. protocol UserViewModel { var id: String { get } var userName: String { get } var email: String? { get } var memberSince: NSDate? { get } var isMe: Bool { get } }
33. extension User : UserViewModel { var id: String { return String(self.userId) } var userName: String { return self.name ?? NSLocalizedString( "NoUsername.DefaultName", comment: "Default name for users with no name”) } var memberSince: NSDate? { return DateParser.fromString(self.memberSinceDate) } var isMe: Bool { get { return String(User.ObtenerInstancia().userId) == id } } }
34. Inject presenters in existing ViewControllers so you can control the flow
35. Study the old code, thoroughly
36. Pick your first battle, don’t go all Chuck Norris on the old code
37. Implement the full architecture
38. Re implementa la feature elegida por completo en la nueva arquitectura No te preocupes por el código duplicado en este punto, es totalmente normal Reimplement the chosen feature in the new architecture
39. Add scaffolding and seams to connect the old with the new
40. Scaffolding?
41. Intermediate code to glue the old architecture with the new one
42. Make it super easy for the code reader to identify scaffolding code UserScaffolding
43. Centralize the scaffolding code per feature UserScaffolding
44. Seams?
45. A place in our code base where we can alter behaviour without being forced to edit it in that place
46. For example, if you don’t want to change the getInstance calls, add a setInstance method to alter that behavior from the outside
47. End of scaffolding and seams
49. One does not simply Put code in production One just
50. Release fast and release often
51. KAIZEN
52. New Old Old Scaffold Scaffold New Old Old New Old Old Scaffold Scaffold
53. If a smelly part is small enough, throw it away and rewrite it
54. It is easier to replace code that is barely used
55. SUMMARY
56. Strategist
57. +
58. Surgeon
59. +
60. Demolition ball
61. Thanks!
62. Questions?