Understand

Legacy Code

Change Messy Software Without Breaking It

💡 Latest articles

• The key points of Refactoring at Scale

  Maude Lemaire wrote a great book rooted from her experience in the trenches, at Slack. Let's see how it may help you lead large-scale refactoring projects.

• The key points of Refactoring

  This book is a catalog of the bread-and-butter moves that can improve your coding game. Let's see what makes it a reference for any professional developer.

• The key points of Kill It with Fire

  Let's rewrite the whole thing on a modern stack! Or should we? Marianne Bellotti offers a lot of wisdom in her book. Here are some examples…

• How to efficiently practice refactoring katas

  How to best learn out of refactoring exercises, depending on your level of experience.

• It's like coding in the dark!

  A look into Catherine Hicks' white paper "It’s Like Coding in the Dark: The need for learning cultures within coding teams" (Catharsis Consulting).

• 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

Few books dig into the challenges of working with legacy systems. These ones do.

Here is my personal bookshelf. For each book, I've written a high-level overview of what you can expect from it. Their salient points, according to me.

Click the ones that intrigue you to get more details. I put the ones that were the most insightful to me first.

Working Effectively with Legacy Code

Refactoring: Improving the Design of Existing Code

Software Design X-Rays

Legacy Code: First Aid Kit

The Programmer's Brain

Refactoring at Scale

Kill It with Fire

Beyond Legacy Code

The Legacy Code Programmer's Toolbox

Re-Engineering Legacy Software

📖 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.

• AI Support

  Can you leverage AI to tame legacy codebases? Let's explore…

🎧 If you prefer podcasts

• Improving Legacy Code

  I discuss with Sam Taggart about my book, Legacy Code: First Aid Kit. We cover the tools and examples that I find most useful when working with legacy code. We briefly touch on the role of AI and other tools I've discovered since I wrote the book.

• 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.