Experiences with dealing with legacy code while delivering value. Key points: 1) Legacy code costs a lot. 2) Design must be maintained & evolved. 3) Continous refactoring during each task is a way to achieve 2.

1. An Agile Approach to
Technical Debt
Is The Only Way
Jakub Holý @ iterate no

2. Origins

3. by Jon Baldock nz @ flickr
We've all been there - mess of code

4. by Ignaz Wiradi @ wikimedia
What we would like to have
- clean, structured, fitting

5. by cotallo-nonocot @ flickr
What we do have. It (likely) started with st. small & clean but requirements evolved
while the design of the code did not - only hacked & patched

6. God class
● 15 kLOC
● 300 properties
● 320 methods
● 50 constants
● used everywhere
by mandalinarossa @ flickr
Example of legacy - a typical monstrous god class that we were confronted with.

7. The pain!
It was pain!

8. True cost of legacy
Pain <= Time wasted in code archeology, money & time wasted due to bugs being
introduced.
Legacy code matters to business for real money are wasted there.

9. Escape???

10. Refactor!
The only way out is to improve the design

11. ?
How do we get from L to R? The sad answer is we don't.
It took centuries to build R. We can never get from L to R in a reasonable time. There
is too much mess, too much to fix.

12. Code Churn
Michael Feathers: Getting Empirical about Refactoring
Code-churn driven refactoring: improve where it matters & pays off most - complex &
changed often

13. => Boy Scout Refactoring
● Only task-related
● Time-boxed
● Always
● (+ TDD)
Refactoring can go on forever => focus, time-box. Task related => in code that
matters most now/in near future. (We: 1/3 every task devoted to refactoring.)

14. Refactoring: Improving the Design of Existing
Code
Martin Fowler
Working Effectively with Legacy Code
Michael Feathers
Behead Your Legacy Beast: The Mikado
Method
D. Brolund, O. Ellnestam

15. It worked!

16. Required:
Management endorsement

17. True cost of legacy
Show to your management; Legacy code = lot of money lost.

18. Challenge
Large-scale refactorings
● risky => avoid
● sometimes necessary
● boy scout rule doesn't help

19. Summary
● Design needs love
● Continuous, focused, time-boxed refactoring
● True cost of legacy

20. You too can do it!

21. Recommended
Retrospectives: Group code reviews:
改 Observe
Evaluate
Teach
Learn
善 Adjust Unify
Something that worked great for us

22. Questions?
@HolyJak
jakub.holy@iterate.no
theholyjava.wordpress.com