How the Medium iOS team works effectively with legacy code

Medium's iOS codebase is over 10 years old with code from 2013 still running in production. Instead of rewriting, they wear it as a badge of honor.

Zouhair Mahieddine from Medium's iOS team shares how they effectively work with legacy code using techniques from Michael Feathers' classic book. The team manages a decade-old codebase while continuously shipping new features without massive rewrites.

Key Takeaways

• Use Sprout methods to add SwiftUI features without touching legacy UIKit code
• Sketch diagrams when confused: they refactored Dark mode by mapping the system first
• Preserve signatures and lean on compiler errors to safely remove dependencies
• Modularize incrementally: SPM modules naturally discourage writing in the monolith
• Extract responsibilities before refactoring: identify what code does, then restructure step by step

The article reveals how they removed an entire Objective-C async library by letting the compiler guide them through every necessary change.