1. Legacy Code : Rehab
A Workshop with @johnnonolan
Friday, 26 April 13

2. • Spent a few years thinking about rewrites.
• Not an expert/guru.
• Written a load of crap.
Me
Friday, 26 April 13

3. What is legacy?
• Code without tests?
• Old tech?
• Not the latest thing?
• Not invented here?
Friday, 26 April 13

4. Is legacy so bad?
Outside of software, how do we see legacy?
Friday, 26 April 13

5. Theres no getting away with
it
Legacy is everywhere
Friday, 26 April 13

6. 2 choices
Rebuild or Renovate
Photo by John T Pilot
Friday, 26 April 13

7. • Estimates always wrong.
• New bugs.
• Secret knowledge in the code.
• Lengthy code freeze.
• Organisation needs to wait for new features.
Risks of Re-building
Friday, 26 April 13

8. But Renovating?
• The code is a mess.
• You don't know where to start.
• It has become poorly designed.
• It is typically untested.
Friday, 26 April 13

9. Botch it then?
• Just hack the change in.
• Code will be worse.
• Which leads to worse code.
Friday, 26 April 13

10. Right let's do it!
• Scratch refactor
• Tell the story of the system
• Sketches
• Characterization tests
• Golden Master technique
Friday, 26 April 13

11. Code Sample
Trivia Code base
https://github.com/jbrains/trivia
Friday, 26 April 13

12. Scratch refactor
• Start playing with the code.
• Throw away the changes.
Friday, 26 April 13

13. Telling the story?
• Just the essentials
• Then move on to more granular bits
• Rinse & repeat.
Friday, 26 April 13

14. Sketches
• Feature sketches
• Effect Sketches
• Effect analysis
Friday, 26 April 13

15. Characterization tests
• Fail
• Pass
• Sensing variables
• Inheritance
• change access modifier
• Throwaway?
Friday, 26 April 13

16. New Feature
Friday, 26 April 13

17. Thanks
• This session is all about understanding the impact of
change.
• Small safe steps.
• Vices.
Friday, 26 April 13

18. Feedback
Email : johnnonolan@gmail.com
Twitter: @johnnonolan
Friday, 26 April 13