Beware of the legacy! The one you inherit and the one you create

In this talk, we’re going to take a look at what problems we face when working with a legacy code base. We’ll explore and evaluate strategies that help you make changes with confidence and steps you can take to make the person who works with your legacy code not hate you! We show you tricks and tools so that you can find hidden dead code and references and will look at ways how you can work more efficiently with a grown codebase.

Transcript

1. BEWARE OF THE LEGACY! THE ONE YOU INHERIT AND THE ONE YOU CREATE
2. ! Videolabs " @_Caro_n # iOS Dev since 2012 $ worked on Apple Maps.
3. MOTIVATION: ▸ approaches to work with a grown codebase ▸ create a great legacy yourself ▸ talk about common pitfalls
4. WHAT IS LEGACY CODE?
5. [Legacy code] is code maintained by an administrator that did not develop the code George Olivetti
6. To me, legacy code is simply code without tests Michael C. Feathers, Working Effectively with Legacy Code
7. Code is legacy code as soon as it's written A Developer
9. Problems with Legacy Code
11. BRITTLE
12. SLOW DEVELOPMENT
13. DEMORALIZING
14. CREATING A GREAT LEGACY
15. ▸ easier understandable code ▸ robust ▸ speed up development ▸ codebase that is fun to work with
17. PROJECT SETUP ▸ work with Pullrequests ▸ setup a Continous Integration ▸ build all platforms with the lowest supported OS
18. DANGER ▸ Enforce CHANGELOGs ▸ Enforce links to Trello/JIRA in PR/MR bodies ▸ Enforce using descriptive labels ▸ Look out for common anti-patterns ▸ Highlight interesting build artifacts ▸ Give specific files extra focus
19. SWIFTLINT ▸ define rules for code style ▸ keeps code consistent ▸ restrict functions by number of lines
20. AUTOMATE LOCALIZABLE FILES ▸ update_string.py by Frédéric Sagnes ▸ extract strings
21. FASTLANE ▸ automates releases ▸ add project specific steps
22. CLEANING UP THE CODE
24. WHEN A REWRITE IS USEFUL ▸ you overhaul a big feature ▸ you switch programming languages
25. LEGACY CODE IS VALUABLE
26. INCREMENTAL CHANGE
27. IDENTIFYING PLACES FOR CHANGE ▸ find the code piece that causes the most pain ▸ that's being touched the most ▸ that causes the most regressions when being changed
29. WRITE TESTS!
30. BENEFITS OF WRITING TESTS ▸ you think about edgecases ▸ it gives you confidence when you touch that code ▸ speeds you up because even if you have it just partly tested you know where not to look
31. write a testsheet
33. ADDING A FEATURE
34. SPROUT METHOD & SPROUT CLASS ▸ write new code in methods ▸ pass needed parameters ▸ return what needs to be returned
36. WRAP METHOD & WRAP CLASSES ▸ adds functionality in new method ▸ calls the old code or old class
38. REFACTORING
39. UNDERSTAND
40. DOCUMENT
41. EXTRACTION METHOD ▸ goal: break up or separate big existing functions ▸ identifying well encapsulated blocks
43. EXTRACTING BOOLS if _repeatMode != VLCRepeatCurrentItem && mediaListCount > 2 && _shuffleMode { ... } to BOOL canShuffle = _repeatMode != VLCRepeatCurrentItem && mediaListCount > 2; if canShuffle && _shuffleMode { ... }
44. FEATURE FLAGS ▸ Used to turn on new features ▸ Can be used to switch between new and old implementations
45. FINDING DEAD CODE ▸ Grep is your friend ▸ cocoapods not removing references ▸ static analyzer to find code that never gets called
46. SUMMARY: ▸ Automate as much as you can ▸ How to incrementally add tests ▸ Add features without piling onto old code ▸ Refactor step by step
48. Resources: Working Effectively with Legacy Code - Michael Feathers Beyond Legacy Code - David Scott Bernstein Refactoring - Kent Beck and Martin Fowler http://samuelmullen.com/articles/legacy_isnt_a_bad_word/ https://www.objc.io/issues/1-view-controllers/lighter-view- controllers/
49. THANKS!