Kotlin at Trello: Mobile Development Best Practices
Article Summary
Vishnu Rajeevan from Trello shares how his team went from 0% to 30.8% Kotlin in just over a year. Their strategy? Start with tests, then make every new feature Kotlin-only.
Trello's Android team adopted Kotlin in October 2016, right after version 1.0.4 launched. This post documents their journey from cautious experimentation to full commitment, including the team mandate that drove adoption: all new features in Kotlin, and any old feature updates must be converted first.
Key Takeaways
- Started with tests as low-risk entry point before building production features
- Grew from 15% to 30.8% Kotlin in six months with aggressive adoption
- Team rule: convert old features to Kotlin before making any updates
- Compile speeds improved, Kotlin no longer causes major build slowdowns
Trello successfully scaled Kotlin adoption to nearly one-third of their codebase by starting small with tests, then enforcing Kotlin-first rules for all new work.
About This Article
Trello's Android team worried about how fast the Kotlin compiler would run and whether the language was ready for production. When version 1.2.0 came out, bugs in the standard library showed up within a day.
Vishnu Rajeevan's team started by writing tests in Kotlin to see if it would work for them before using it in actual features. After that worked out, they made a rule that any updates to old features had to be rewritten in Kotlin before the team could move forward.
Compilation times got much faster once they switched to Kotlin, and Kapt stopped slowing down their builds. This let them feel confident enough to use Kotlin everywhere in their workflow, including tests, new features, and updates.