The Journey to Compose Hot Reload 1.0.0
Article Summary
Sebastian Sellmair and Azat Abdullin from JetBrains reveal how they built Compose Hot Reload 1.0.0—a zero-config tool that lets you update Kotlin UI code instantly while preserving app state. The engineering behind it is wild.
Compose Hot Reload 1.0.0 just shipped with Compose Multiplatform 1.10, enabling developers to see code changes reflected in running apps without restarts. This deep dive from the JetBrains team unpacks the technical architecture: DCEVM for dynamic code reloading, bytecode analysis for UI invalidation, and a custom orchestration protocol connecting IDE, build system, and runtime.
Key Takeaways
- DCEVM in JetBrains Runtime enables unrestricted class redefinition beyond standard JVM limits
- Custom Java agent analyzes Compose bytecode to track UI groups and invalidate only changed code
- Zero configuration: Gradle plugin auto generates hot reload tasks and manages incremental compilation
- Orchestration protocol coordinates IDE, build system, and app without external dependencies
- Team fixed compiler lambda naming issues causing reload failures across Kotlin versions
Compose Hot Reload combines JetBrains Runtime's DCEVM, bytecode analysis, and build system integration to deliver instant UI updates with state preservation and zero developer configuration.
