Presented at Chester Devs 06/02/2013

1. L egacy Cod e : Rehab
lan
A Workshop with @johnnono

2. Me
● Spent a few years thinking about rewrites.
● Not an expert/guru.
● Written a load of crap.

3. What is legacy?
● Code without tests?
● Old tech?
● Not the latest thing?
● Not invented here?

4. Is lega cy so bad?
Outside of software, how do we see legacy?

5. getting aw ay with it
Theres no
Legacy is everywhere

6. 2 choices
Photo by John T Pilot
Rebuild or Renovate

7. Risks of R e-building
● Estimates always wrong.
● New bugs.
● Secret knowledge in the code.
● Lengthy code freeze.
● Organisation needs to wait for new
features.

8. But Renovating?
● The code is a mess.
● You don't know where to start.
● It has become poorly designed.
● It is typically untested.

9. Bot ch it then?
● Just hack the change in.
● Code will be worse.
● Which leads to worse code.

10. Right let's do it!
● Scratch refactor
● Tell the story of the system
● Sketches
● Characterization tests

11. Cod e Sample
Trivia Code base
https://github.com/jbrains/trivia

12. Scratch refactor
● Start playing with the code.
● Throw away the changes.

13. Telling the story?
● Just the essentials
● Then move on to more granular bits
● Rinse & repeat.

14. Sketches
● Feature sketches
● Effect Sketches
● Effect analysis

15. C haracteriz ation tests
● Fail
● Pass
● Sensing variables
● Inheritance
● change access modifier
● Throwaway?

16. New Feature

17. Thanks
● This session is all about understanding the
impact of change.
● Small safe steps.
● Vices.

18. Feedback
Email : johnnonolan@gmail.com
Twitter: @johnnonolan