The PDF provides a (page 34), showing how it tracks the Column -> Text -> Button hierarchy with positional indexes. Without this diagram, developers often wrongly assume Compose compares entire UI trees like a diffing algorithm (React). It does not. It uses positional memoization . Core Concept #2: The Compiler Transformation (The Magic) If you write:
Download the Jetpack Compose Internals PDF today and finally understand the framework you use every day. This article contains updated information based on Compose 1.6.8, Kotlin 2.0.20, and AGP 8.5.0. Last verified: October 2025.
A developer notices their LazyColumn recomposes every item when scrolling, even though data hasn’t changed. jetpack compose internals pdf download new
fun Greeting(name: String, composer: Composer, changed: Int) { composer.start(123) // Group ID for "Greeting" if (changed or 0b1 != 0) { Text("Hello $name", composer) } else { composer.skipToGroupEnd() } composer.end() } Every @Composable function receives a Composer parameter. The start and end calls mark groups in the Slot Table. The changed bitmask tells Compose whether the inputs ( name ) have changed since the last run.
val itemLambda = remember { @Composable { MessageItem(message) } } LazyColumn { items(count = messages.size) { index -> itemLambda() } } The PDF explains why this works: remember caches the composable lambda instance in the Slot Table. The parent recomposition passes a , triggering the skip path. How to Download the "Jetpack Compose Internals" PDF (New Version) Given that this is a sought-after resource, there are several ways to access the legitimate, updated PDF: Option 1: Official Publisher (Recommended) The completely updated "Jetpack Compose Internals: A Journey Through the Runtime, Compiler, and UI Layer" (3rd Edition) is now available for digital download from AndroidInternalsPress . The PDF is DRM-free, includes over 50 diagrams, and comes with sample code repositories. The PDF provides a (page 34), showing how
In Compose 1.6+, with Strong Skipping Mode enabled, the compiler generates even smarter code that skips entire functions if all parameters are stable (immutable or primitive). The PDF shows you how to enable this in your gradle.properties :
For years, developers have asked for a single, consolidated resource that explains the without forcing you to read thousands of lines of AOSP source code. That resource has finally arrived. It uses positional memoization
LazyColumn uses LazyListScope . Each item {} block is a restartable composable lambda . Without strong skipping, Compose compares lambda references, not content. If the lambda is recreated on every recomposition, all items recompose.