add StateFlow<T>.mapState, combineStates(StateFlow<T>...)
#317
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## master #317 +/- ##
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- Coverage 88.38% 76.35% -12.04%
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Lines 801 939 +138
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Pull Request Overview
This PR adds new StateFlow utility functions to the FlowExt library, providing convenient methods for mapping and combining StateFlow instances while preserving their state characteristics.
- Adds
StateFlow<T>.mapState()extension function for transforming StateFlow values - Adds
combineStates()functions with 2-12 parameter overloads for combining multiple StateFlows - Includes comprehensive test coverage and API documentation
Reviewed Changes
Copilot reviewed 5 out of 8 changed files in this pull request and generated 11 comments.
Show a summary per file
| File | Description |
|---|---|
| src/commonMain/kotlin/com/hoc081098/flowext/StateFlows.kt | New file implementing mapState and combineStates functions with internal StateFlow implementations |
| src/commonTest/kotlin/com/hoc081098/flowext/MapStateTest.kt | Test file covering mapState functionality and readonly state flow validation |
| src/commonTest/kotlin/com/hoc081098/flowext/utils/BaseTest.kt | Added helper function for validating readonly StateFlow instances |
| api/FlowExt.api | Updated API dump reflecting new public functions |
| api/FlowExt.klib.api | Updated Kotlin library API dump |
Files not reviewed (2)
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| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, T4, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, T4, T5, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, T4, T5, T6, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, T4, T5, T6, T7, T8, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, T4, T5, T6, T7, T8, T9, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
| * @see mapState | ||
| */ | ||
| @FlowExtPreview | ||
| public fun <T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, R> combineStates( |
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There's an extra period at the end of the documentation comment. Remove the double period in 'transform function..'
|
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| @FlowExtPreview | ||
| public fun <T1, T2, R> combineStates( | ||
| flow1: StateFlow<T1>, | ||
| flow2: StateFlow<T2>, | ||
| transform: (T1, T2) -> R, | ||
| ): StateFlow<R> = | ||
| DerivedStateFlow( | ||
| source = combine(flow1, flow2, transform), | ||
| valueSupplier = { transform(flow1.value, flow2.value) }, | ||
| ) |
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[P2] Avoid emitting unchanged values in combineStates
mapState applies distinctUntilChanged() so derived state only notifies observers when the mapped value actually changes, but all combineStates overloads feed combine(...) directly into DerivedStateFlow without a deduplication step. When inputs change but transform evaluates to the same result (e.g., combining two StateFlow<Boolean> with || while each flow toggles), collectors will receive identical values repeatedly, causing unnecessary downstream work and breaking the typical StateFlow expectation that equal values are suppressed. Consider applying distinctUntilChanged() after combine(...) so only meaningful state changes propagate.
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