Decomposing Compose

on YouTube ↗59m

" summary

Shows how Jetpack Compose actually turns Kotlin UI functions into bytecode: the compiler plugin injects extra parameters (a Composer and an int), emits startRestartGroup/endRestartGroup calls and bitmask flags, and the runtime stores UI nodes in a gap buffer to skip or recompose only changed groups. Uses IntelliJ, javap -v -p and Kotlin compiler inspection to reproduce a button+counter example and explain why JaCoCo sees mysterious branches; investigation reproduces the issue but the JaCoCo ticket remains unfixed.

AI-written summary · about

" chapters (11)

1. 0:00Introduction
2. 4:26What is Compose
3. 12:54Jacoco issues with Compose
4. 21:55Compose components
5. 25:04Compose bytecode changes
6. 31:57Parameters and states in Compose
7. 39:46Default parameters in Compose
8. 44:18Lambdas and control flow in Compose
9. 47:50Compose redraw optimization
10. 51:01Bytecode analysis importance
11. 53:53Q&A

" related talks

• 19mJumping into Jetpack Compose way too early to see what's insideLouis Tsai · droidCon Berlin 2019
• 29mA Hitchhiker's Guide to Compose Compiler: Composers, Compiler Plugins, and SnapshotsAmanda Hinchman-Dominguez, Jossi Wolf · droidcon New York 2022
• 28mA Hitchhiker's Guide to Compose Compiler: Composers, Compiler Plugins, and SnapshotsAmanda Hinchman-Dominguez, Jossi Wolf · droidcon San Francisco 2022
• 40mJetpack Compose MechanismsJaewoong (skydoves) · DroidKaigi 2026
• 40mThe Compose Runtime, DemystifiedLeland Richardson · KotlinConf 2019
• 01h 00mJetpack Compose - Next Gen Kotlin UI Toolkit for AndroidRagunath Jawahar · Kotlin/Everywhere 'Namma' Bengaluru 2019
• 27mInside Jetpack Composetakahirom · DroidKaigi 2021
• 32mJetpack Compose — Next Gen Kotlin UI Toolkit for AndroidRagunath Jawahar · droidCon Berlin 2019