Understand

Legacy Code

Change Messy Software Without Breaking It

💡 Latest articles

• Delete unused code (and how to retrieve it)

  Dead code adds noise to the codebase and should be deleted. Yet, deleted code feels harder to retrieve. Here's how to find such code easily with git!

• Can AI help me refactor legacy code?

  Can assistants like ChatGPT refactor existing code without introducing bugs? Let's figure it out with an actual codebase.

• Can AI help me write tests on legacy code?

  People are using tools like ChatGPT to write tests on existing code… But how reliable is this? Let's find out!

• Fake it until you automate it

  A pragmatic way for you to start automating deployments of a Legacy system.

• Comparing 2 approaches of refactoring untested code

  You need to change code that's not tested. How do you know you didn't break something? Let's compare 2 ways of doing that!

• If you want more, check all my published articles

🥋 Specific techniques

• Approval Testing

  A technique to quickly put tests on Legacy Code, so you can refactor safely.

• Behavioral Analysis

  A technique to get insights from large codebases, using VCS information.

• Draw Dependency Graphs

  A technique to understand the structure of a codebase.

📚 Useful books on Legacy Code

• The key points of The Programmer's Brain

  This book analyses how your brain works and gives concrete advice to help you work with Legacy Code. Here's my summary of its salient points.

• The key points of Re-Engineering Legacy Software

  Here's an interesting book on approaching Legacy Software. Here's my summary of its salient points.

• The key points of Beyond Legacy Code

  This book is filled with practical strategies to apply on Legacy systems. Here's my summary of its salient points.

• The key points of The Legacy Code Programmer's Toolbox

  This book is full of tips to get into an unfamiliar codebase. Here's my summary of its salient points.

• The key points of Software Design X-Rays

  This book is a gold mine. Yet, it's not a famous one. Here's my summary of its salient points that can help you deal with large codebases.

• The key points of Working Effectively with Legacy Code

  This book is a reference. Here's my summary of its salient points so you understand why it's so recommended.

📖 Helpful Guides

• Getting into a large codebase

  Diving into a large, undocumented codebase is overwhelming. Let's see some techniques to approach it.

• Best practice or a code smell?

  Not sure if a pattern will make the code more maintainable? Here are a few resources that will help.

• Changing untested code without breaking it

  Without tests, every code change is risky. But how to put tests on a code that wasn't design for it?

• Code feels impossible to maintain

  Sometimes, you seem to hit a point of no return and that the best strategy would be to burn it all and start over. Are there alternatives?

• Making others care about it

  What you can do when it seems that no-one cares about the technical debt that's piling up.

🎧 If you prefer podcasts

• Tips for Working with Legacy Code

  I talk with Jason Swett about working with legacy code, adding tests to legacy code, how to safely make changes to legacy applications, and more.

• Changing Messy Software Without Breaking It

  I talk with Robby Russell about practices like feature toggling or sustainability weeks to work on improving things. I also give advice for listeners who struggle to get stakeholder buy-in on dealing with technical debt challenges.

🎤 If you prefer talks

• 7 techniques to tame a Legacy Codebase

  You spend most of our time changing existing code that is not documented, nor tested! It's painful because you're always in a hurry to ship new features and bug fixes… What if you had a secret weapon to make things better as you go? Here are 7 concrete techniques that will help you regain control of your Legacy.

• 3 must-watch talks on Legacy Code

  I have hosted more than 37 speakers to talk about Legacy Code tips and tricks. Here is my top 3 of the talks you should probably watch!

• Testability, Empathy, and Safe Refactorings

  4 great talks on Legacy Code that I had the pleasure to host. This edition particularly focuses on testing and refactoring.

• DevOps, Living Documentation, and Hexagonal Architecture

  5 great talks on Legacy Code that I had the pleasure to host. This edition raises new topic such as documentation and legacy pipelines.

• Design Patterns, Empathy, and Reading Complex Code

  4 great talks on Legacy Code that I had the pleasure to host. A focus on empathy and getting into complex codebases.

• Technical Debt, Rewrites, and Refactoring

  5 great talks on Legacy Code that I had the pleasure to host. Learn how to prioritize Tech Debt and rewrite systems incrementally.

• Refactoring, Unit Tests, and Symmathesy

  5 great talks on Legacy Code that I had the pleasure to host. Learn how to progressively migrate existing codebase towards a better state.

• Approval Tests, TCR, and Menders

  5 great talks on Legacy Code that I had the pleasure to host. Learn how to test existing code and approach unfamiliar codebases.

• 5 talks on Legacy Code: The Legacy of SoCraTes, 1st edition

  Tips and advice on dealing with Legacy Code from 5 great speakers at this remote conference I organized for the community.

Written by Nicolas Carlo who lives and works in Montreal, Canada 🍁
He founded the Software Crafters Montreal community which cares about building maintainable softwares.