(#) `State` will autobox values assigned to this state. Use a specialized state type instead. !!! Tip: `State` will autobox values assigned to this state. Use a specialized state type instead. Advice from this check is just a hint; it's a "weak" warning. Id : `AutoboxingStateCreation` Summary : `State` will autobox values assigned to this state. Use a specialized state type instead. Severity : Hint Category : Performance Platform : Any Vendor : Jetpack Compose Identifier : androidx.compose.runtime Feedback : https://issuetracker.google.com/issues/new?component=612128 Min : Lint 8.7+ Compiled : Lint 8.7+ Artifact : [androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-android.md.html) Since : 1.5.0 Affects : Kotlin and Java files Editing : This check runs on the fly in the IDE editor Implementation : [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/main/java/androidx/compose/runtime/lint/AutoboxingStateCreationDetector.kt) Tests : [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/test/java/androidx/compose/runtime/lint/AutoboxingStateCreationDetectorTest.kt) Copyright Year : 2023 Calling `mutableStateOf()` when `T` is either backed by a primitive type on the JVM or is a value class results in a state implementation that requires all state values to be boxed. This usually causes an additional allocation for each state write, and adds some additional work to auto-unbox values when reading the value of the state. Instead, prefer to use a specialized primitive state implementation for `Int`, `Long`, `Float`, and `Double` when the state does not need to track null values and does not override the default `SnapshotMutationPolicy`. See `mutableIntStateOf()`, `mutableLongStateOf()`, `mutableFloatStateOf()`, and `mutableDoubleStateOf()` for more information. !!! Tip This lint check has an associated quickfix available in the IDE. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/androidx/compose/runtime/lint/test/test.kt:8:Information: Prefer mutableStateOf instead of mutableStateOf [AutoboxingStateCreation] val state = mutableStateOf<>() -------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/androidx/compose/runtime/lint/test/test.kt`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers package androidx.compose.runtime.lint.test import androidx.compose.runtime.* import fun valueAssignment() { val state = mutableStateOf<>() state.value = } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/test/java/androidx/compose/runtime/lint/AutoboxingStateCreationDetectorTest.kt) for the unit tests for this check to see additional scenarios. The above example was automatically extracted from the first unit test found for this lint check, `AutoboxingStateCreationDetector.testTrivialMutableStateOf_thatCouldBeMutablePrimitiveStateOf`. To report a problem with this extracted sample, visit https://issuetracker.google.com/issues/new?component=612128. (##) Including !!! This is not a built-in check. To include it, add the below dependency to your project. ``` // build.gradle.kts implementation("androidx.compose.runtime:runtime-android:1.9.0-alpha01") // build.gradle implementation 'androidx.compose.runtime:runtime-android:1.9.0-alpha01' // build.gradle.kts with version catalogs: implementation(libs.runtime.android) # libs.versions.toml [versions] runtime-android = "1.9.0-alpha01" [libraries] # For clarity and text wrapping purposes the following declaration is # shown split up across lines, but in TOML it needs to be on a single # line (see https://github.com/toml-lang/toml/issues/516) so adjust # when pasting into libs.versions.toml: runtime-android = { module = "androidx.compose.runtime:runtime-android", version.ref = "runtime-android" } ``` 1.9.0-alpha01 is the version this documentation was generated from; there may be newer versions available. NOTE: These lint checks are **also** made available separate from the main library. You can also use `androidx.compose.runtime:runtime-lint:1.9.0-alpha01`. [Additional details about androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-android.md.html). (##) Suppressing You can suppress false positives using one of the following mechanisms: * Using a suppression annotation like this on the enclosing element: ```kt // Kotlin @Suppress("AutoboxingStateCreation") fun method() { mutableStateOf(...) } ``` or ```java // Java @SuppressWarnings("AutoboxingStateCreation") void method() { mutableStateOf(...); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection AutoboxingStateCreation problematicStatement() ``` * Using a special `lint.xml` file in the source tree which turns off the check in that folder and any sub folder. A simple file might look like this: ```xml <?xml version="1.0" encoding="UTF-8"?> <lint> <issue id="AutoboxingStateCreation" severity="ignore" /> </lint> ``` Instead of `ignore` you can also change the severity here, for example from `error` to `warning`. You can find additional documentation on how to filter issues by path, regular expression and so on [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html). * In Gradle projects, using the DSL syntax to configure lint. For example, you can use something like ```gradle lintOptions { disable 'AutoboxingStateCreation' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore AutoboxingStateCreation ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).