How we used Macros to Promote MVVM architecture adoption

Duolingo's iOS team turned a boilerplate problem into a Swift Macros showcase. Their codebase grew, but developer friction didn't have to.

As Duolingo's iOS team scaled, they standardized on MVVM architecture but hit a wall with repetitive DataSource code. Carter Levin shares how they used Swift Macros to generate boilerplate automatically while keeping build times in check.

Key Takeaways

• 4,300 lines of code now auto-generated, never written, reviewed, or tested
• Macros operate on AST at compile time, fully integrated into Swift compiler
• Manual binary linking via S3 cache avoided 10-20 second build time hits
• DataSources were ideal: consistent patterns but hard to abstract with generics
• Generated code is standardized, tested, and less prone to manual errors

The build time optimization strategy involving S3 caching and manual binary linking is worth the read alone.