Legacy Code : Rehab

A Workshop with @johnnonolan

Friday, 26 April 13

• Spent a few years thinking about rewrites.

• Not an expert/guru.

• Written a load of crap.

Me

Friday, 26 April 13

What is legacy?• Code without tests?

• Old tech?

• Not the latest thing?

• Not invented here?

Friday, 26 April 13

Is legacy so bad?Outside of software, how do we see legacy?

Friday, 26 April 13

Theres no getting away with it

Legacy is everywhere

Friday, 26 April 13

2 choices

Rebuild or RenovatePhoto by John T Pilot

Friday, 26 April 13

• 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

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

Botch it then?• Just hack the change in.

• Code will be worse.

• Which leads to worse code.

Friday, 26 April 13

Right let's do it!• Scratch refactor

• Tell the story of the system

• Sketches

• Characterization tests

• Golden Master technique

Friday, 26 April 13

Code SampleTrivia Code base

https://github.com/jbrains/trivia

Friday, 26 April 13

Scratch refactor• Start playing with the code.

• Throw away the changes.

Friday, 26 April 13

Telling the story?• Just the essentials

• Then move on to more granular bits

• Rinse & repeat.

Friday, 26 April 13

Sketches• Feature sketches

• Effect Sketches

• Effect analysis

Friday, 26 April 13

Characterization tests• Fail

• Pass

• Sensing variables

• Inheritance

• change access modifier

• Throwaway?

Friday, 26 April 13

New Feature

Friday, 26 April 13

Thanks• This session is all about understanding the impact of

change.

• Small safe steps.

• Vices.

Friday, 26 April 13

FeedbackEmail : johnnonolan@gmail.com

Twitter: @johnnonolan

Friday, 26 April 13