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persisting_state_of_components.md: Describe SerializablePersistentStateComponent

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topics/basics/persisting_state_of_components.md
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@ -34,24 +34,61 @@ If an extension needs to have a persistent state, define a separate service resp
<tabs group="languages">
<tab title="Kotlin" group-key="kotlin">
The easiest way to implement a persistent state component in Kotlin is extending [`SimplePersistentStateComponent`](%gh-ic%/platform/projectModel-api/src/com/intellij/openapi/components/SimplePersistentStateComponent.kt), which implements `PersistentStateComponent`.
The recommended approach to implementing a persistent state component in Kotlin is to extend one of the base classes:
1. [`SimplePersistentStateComponent`](#SimplePersistentStateComponent)
2. [`SerializablePersistentStateComponent`](#SerializablePersistentStateComponent) (available since 2022.2)
`SimplePersistentStateComponent` is parameterized by a subclass of [`BaseState`](%gh-ic%/platform/projectModel-api/src/com/intellij/openapi/components/BaseState.kt).
<chapter title="SimplePersistentStateComponent" id="SimplePersistentStateComponent">
[`SimplePersistentStateComponent`](%gh-ic%/platform/projectModel-api/src/com/intellij/openapi/components/SimplePersistentStateComponent.kt) is parameterized by a subclass of [`BaseState`](%gh-ic%/platform/projectModel-api/src/com/intellij/openapi/components/BaseState.kt).
`BaseState` provides a set of handy [property delegates](https://kotlinlang.org/docs/delegated-properties.html), which make it easy to create properties with default values.
In addition, delegates track property modifications internally, which helps decrease calling `PersistentStateComponent.getState()` by the platform.
It is recommended to create separate classes for a component and its state:
Example:
```kotlin
@Service
@State(...)
class MySettings : SimplePersistentStateComponent<MyState>(MyState())
class MyState : BaseState() {
var value by string()
class MySettings : SimplePersistentStateComponent<MySettings.State>(State()) {
class State : BaseState() {
var value by string("default value")
}
}
```
</chapter>
<chapter title="SerializablePersistentStateComponent" id="SerializablePersistentStateComponent">
<primary-label ref="2022.2"/>
[`SerializablePersistentStateComponent`](%gh-ic%/platform/projectModel-api/src/com/intellij/openapi/components/SerializablePersistentStateComponent.kt) is parameterized with a state data class.
State properties are exposed via persistent state component class' properties.
The state properties are modified by copying the state and overwriting a modified value within `SerializablePersistentStateComponent.updateState()`, which ensures atomic modification.
Example:
```kotlin
@Service
@State(...)
class MySettings : SerializablePersistentStateComponent<MySettings.State>(State()) {
var stringValue: String
get() = state.stringValue
set(value) {
updateState {
it.copy(stringValue = value)
}
}
data class State (
@JvmField val stringValue: String = "default value"
)
}
```
</chapter>
</tab>
<tab title="Java" group-key="java">