AutoboxingStateCreation.md.html

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(#) `State<T>` will autobox values assigned to this state. Use a specialized state type instead.

!!! Tip: `State<T>` will autobox values assigned to this state. Use a specialized state type instead.
   Advice from this check is just a tip.

Id
:   `AutoboxingStateCreation`
Summary
:   `State<T>` will autobox values assigned to this state. Use a specialized state type instead.
Severity
:   Information
Category
:   Performance
Platform
:   Any
Vendor
:   Jetpack Compose
Identifier
:   androidx.compose.runtime
Feedback
:   https://issuetracker.google.com/issues/new?component=612128
Min
:   Lint 8.0 and 8.1
Compiled
:   Lint 8.0 and 8.1
Artifact
:   [androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-android.md.html)

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<T>()` 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&lt;&gt;()
                --------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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:1.7.0-rc01")

// build.gradle
implementation 'androidx.compose.runtime:runtime-android:1.7.0-rc01'

// build.gradle.kts with version catalogs:
implementation(libs.runtime.android)

# libs.versions.toml
[versions]
runtime-android = "1.7.0-rc01"
[libraries]
runtime-android = {
    module = "androidx.compose.runtime:runtime-android",
    version.ref = "runtime-android"
}
```

1.7.0-rc01 is the version this documentation was generated from;
there may be newer versions available.

[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
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="AutoboxingStateCreation" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  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).

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