A talk by Ahmed Omran (@this_ahmed on Twitter) on working with legacy Rails apps, presented at the Ottawa Ruby June 2015 meetup.

1. Working With Legacy
Rails Apps
@this_ahmed

2. Working With Legacy
Rails Apps
@this_ahmed

3. legacy code
• untested code (Michael C. Feathers)
• code someone else wrote (old gems, outsourcing,
maintainers left)
• difficult to work with
• risky to change
• but serves a useful function

4. googling legacy code …

5. every project has
legacy code?

7. • learning & experimenting
• ambitious applications
• big project, developer churn, hiring outside help
• bad code … even with the best of intentions
• “Technical debt”

9. –Robert C. Martin
“Even the most disciplined development team,
knowing the best principles, using the best
patterns, and following the best practices will
create messes from time to time.”

10. in the face of legacy
code you can …

12. or…

14. Useful techniques

15. Rebuild Refactor

16. –Robert C. Martin
“…taking a tangled, opaque, convoluted
system and slowly, gradually, piece by piece,
step by step, turning it into a simple, nicely
structured, well-designed system.”

17. Boy Scout Rule
Clean up around you work area. Small fixes; small
refractors.

18. cover and modify
• add unit test
• test passes
• modify code
• test passes

19. use mock objects to
break dependencies

21. mock dependencies

22. break complicated
dependencies with
seams

24. seam => put in method + stub

25. first step to later
refactor

26. i don’t understand this
code…

27. Ask someone

28. code archeology

29. code archeology
git blame / Github

30. code archeology
search code
for context
git blame / Github

31. code archeology
project management
ticket
git blame / Github
search code
for context

32. code archeology
git blame / Github project management
ticket
commit message
search code
for context

33. review
• boy scout rule
• cover and modify
• break dependencies with mocks and seams
• understand code with archeology

34. some parting thoughts

35. unit test

38. • code review
• small git branches
• add lots of context in pull request / commit
message