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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.
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An Agile Approach to Technical Debt
Is The Only Way
Jakub Holý @ iterate no
Origins
by Jon Baldock nz @ flickr
We've all been there - mess of code
by Ignaz Wiradi @ wikimedia
What we would like to have- clean, structured, fitting
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
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.
The pain!
It was pain!
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.
Escape???
Refactor!
The only way out is to improve the design
?
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.
Code Churn
Michael Feathers: Getting Empirical about Refactoring
Code-churn driven refactoring: improve where it matters & pays off most - complex & changed often
=> 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.)
Refactoring: Improving the Design of Existing CodeMartin Fowler
Working Effectively with Legacy CodeMichael Feathers
Behead Your Legacy Beast: The Mikado MethodD. Brolund, O. Ellnestam
It worked!
Required:
Management endorsement
True cost of legacy
Show to your management; Legacy code = lot of money lost.
Challenge
Large-scale refactorings● risky => avoid● sometimes necessary● boy scout rule doesn't help
Summary
● Design needs love● Continuous, focused, time-boxed refactoring● True cost of legacy
You too can do it!
TeachLearnUnify
ObserveEvaluateAdjust
改善
Recommended
Retrospectives: Group code reviews:
Something that worked great for us
