MutableSharedFlow

interface MutableSharedFlow<T> : 
    SharedFlow<T>,
    FlowCollector<T>
(source)

A mutable SharedFlow that provides functions to emit values to the flow. An instance of MutableSharedFlow with the given configuration parameters can be created using MutableSharedFlow(...) constructor function.

See the SharedFlow documentation for details on shared flows.

MutableSharedFlow is a SharedFlow that also provides the abilities to emit a value, to tryEmit without suspension if possible, to track the subscriptionCount, and to resetReplayCache.

Concurrency

All methods of shared flow are thread-safe and can be safely invoked from concurrent coroutines without external synchronization.

Not stable for inheritance

The MutableSharedFlow interface is not stable for inheritance in 3rd party libraries, as new methods might be added to this interface in the future, but is stable for use. Use the MutableSharedFlow(...) constructor function to create an implementation.

Properties

subscriptionCount

abstract val subscriptionCount: StateFlow<Int>

The number of subscribers (active collectors) to this shared flow.

Inherited Properties

replayCache

abstract val replayCache: List<T>

A snapshot of the replay cache.

Functions

emit

abstract suspend fun emit(value: T): Unit

Emits a value to this shared flow, suspending on buffer overflow if the shared flow was created with the default BufferOverflow.SUSPEND strategy.

resetReplayCache

abstract fun resetReplayCache(): Unit

Resets the replayCache of this shared flow to an empty state. New subscribers will be receiving only the values that were emitted after this call, while old subscribers will still be receiving previously buffered values. To reset a shared flow to an initial value, emit the value after this call.

tryEmit

abstract fun tryEmit(value: T): Boolean

Tries to emit a value to this shared flow without suspending. It returns true if the value was emitted successfully. When this function returns false, it means that the call to a plain emit function will suspend until there is a buffer space available.

Extension Properties

coroutineContext

val FlowCollector<*>.coroutineContext: CoroutineContext

isActive

val FlowCollector<*>.isActive: Boolean

Extension Functions

asSharedFlow

fun <T> MutableSharedFlow<T>.asSharedFlow(): SharedFlow<T>

Represents this mutable shared flow as a read-only shared flow.

broadcastIn

fun <T> Flow<T>.broadcastIn(
    scope: CoroutineScope,
    start: CoroutineStart = CoroutineStart.LAZY
): BroadcastChannel<T>

Creates a broadcast coroutine that collects the given flow.

buffer

fun <T> Flow<T>.buffer(
    capacity: Int = BUFFERED,
    onBufferOverflow: BufferOverflow = BufferOverflow.SUSPEND
): Flow<T>

Buffers flow emissions via channel of a specified capacity and runs collector in a separate coroutine.

fun <T> Flow<T>.buffer(capacity: Int = BUFFERED): Flow<T>

cache

fun <T> Flow<T>.cache(): Flow<T>

cancel

fun FlowCollector<*>.cancel(
    cause: CancellationException? = null
): Unit

catch

fun <T> Flow<T>.catch(
    action: suspend FlowCollector<T>.(cause: Throwable) -> Unit
): Flow<T>

Catches exceptions in the flow completion and calls a specified action with the caught exception. This operator is transparent to exceptions that occur in downstream flow and does not catch exceptions that are thrown to cancel the flow.

fun <T> SharedFlow<T>.catch(
    action: suspend FlowCollector<T>.(cause: Throwable) -> Unit
): Flow<T>

collect

suspend fun Flow<*>.collect(): Unit

Terminal flow operator that collects the given flow but ignores all emitted values. If any exception occurs during collect or in the provided flow, this exception is rethrown from this method.

suspend fun <T> Flow<T>.collect(
    action: suspend (value: T) -> Unit
): Unit

Terminal flow operator that collects the given flow with a provided action. If any exception occurs during collect or in the provided flow, this exception is rethrown from this method.

collectIndexed

suspend fun <T> Flow<T>.collectIndexed(
    action: suspend (index: Int, value: T) -> Unit
): Unit

Terminal flow operator that collects the given flow with a provided action that takes the index of an element (zero-based) and the element. If any exception occurs during collect or in the provided flow, this exception is rethrown from this method.

collectLatest

suspend fun <T> Flow<T>.collectLatest(
    action: suspend (value: T) -> Unit
): Unit

Terminal flow operator that collects the given flow with a provided action. The crucial difference from collect is that when the original flow emits a new value, action block for previous value is cancelled.

combine

fun <T1, T2, R> Flow<T1>.combine(
    flow: Flow<T2>,
    transform: suspend (a: T1, b: T2) -> R
): Flow<R>

Returns a Flow whose values are generated with transform function by combining the most recently emitted values by each flow.

combineLatest

fun <T1, T2, R> Flow<T1>.combineLatest(
    other: Flow<T2>,
    transform: suspend (T1, T2) -> R
): Flow<R>
fun <T1, T2, T3, R> Flow<T1>.combineLatest(
    other: Flow<T2>,
    other2: Flow<T3>,
    transform: suspend (T1, T2, T3) -> R
): Flow<R>
fun <T1, T2, T3, T4, R> Flow<T1>.combineLatest(
    other: Flow<T2>,
    other2: Flow<T3>,
    other3: Flow<T4>,
    transform: suspend (T1, T2, T3, T4) -> R
): Flow<R>
fun <T1, T2, T3, T4, T5, R> Flow<T1>.combineLatest(
    other: Flow<T2>,
    other2: Flow<T3>,
    other3: Flow<T4>,
    other4: Flow<T5>,
    transform: suspend (T1, T2, T3, T4, T5) -> R
): Flow<R>

combineTransform

fun <T1, T2, R> Flow<T1>.combineTransform(
    flow: Flow<T2>,
    transform: suspend FlowCollector<R>.(a: T1, b: T2) -> Unit
): Flow<R>

Returns a Flow whose values are generated by transform function that process the most recently emitted values by each flow.

conflate

fun <T> Flow<T>.conflate(): Flow<T>

Conflates flow emissions via conflated channel and runs collector in a separate coroutine. The effect of this is that emitter is never suspended due to a slow collector, but collector always gets the most recent value emitted.

count

suspend fun <T> Flow<T>.count(
    predicate: suspend (T) -> Boolean
): Int

Returns the number of elements matching the given predicate.

debounce

fun <T> Flow<T>.debounce(timeoutMillis: Long): Flow<T>
fun <T> Flow<T>.debounce(timeoutMillis: (T) -> Long): Flow<T>

Returns a flow that mirrors the original flow, but filters out values that are followed by the newer values within the given timeout. The latest value is always emitted.

fun <T> Flow<T>.debounce(timeout: <ERROR CLASS>): Flow<T>
fun <T> Flow<T>.debounce(
    timeout: (T) -> <ERROR CLASS>
): Flow<T>

Returns a flow that mirrors the original flow, but filters out values that are followed by the newer values within the given timeout. The latest value is always emitted.

distinctUntilChanged

fun <T> Flow<T>.distinctUntilChanged(): Flow<T>

Returns flow where all subsequent repetitions of the same value are filtered out.

fun <T> Flow<T>.distinctUntilChanged(
    areEquivalent: (old: T, new: T) -> Boolean
): Flow<T>

Returns flow where all subsequent repetitions of the same value are filtered out, when compared with each other via the provided areEquivalent function.

distinctUntilChangedBy

fun <T, K> Flow<T>.distinctUntilChangedBy(
    keySelector: (T) -> K
): Flow<T>

Returns flow where all subsequent repetitions of the same key are filtered out, where key is extracted with keySelector function.

drop

fun <T> Flow<T>.drop(count: Int): Flow<T>

Returns a flow that ignores first count elements. Throws IllegalArgumentException if count is negative.

dropWhile

fun <T> Flow<T>.dropWhile(
    predicate: suspend (T) -> Boolean
): Flow<T>

Returns a flow containing all elements except first elements that satisfy the given predicate.

emitAll

suspend fun <T> FlowCollector<T>.emitAll(
    channel: ReceiveChannel<T>
): Unit

Emits all elements from the given channel to this flow collector and cancels (consumes) the channel afterwards. If you need to iterate over the channel without consuming it, a regular for loop should be used instead.

suspend fun <T> FlowCollector<T>.emitAll(flow: Flow<T>): Unit

Collects all the values from the given flow and emits them to the collector. It is a shorthand for flow.collect { value -> emit(value) }.

filter

fun <T> Flow<T>.filter(
    predicate: suspend (T) -> Boolean
): Flow<T>

Returns a flow containing only values of the original flow that matches the given predicate.

filterIsInstance

fun <R> Flow<*>.filterIsInstance(): Flow<R>

Returns a flow containing only values that are instances of specified type R.

filterNot

fun <T> Flow<T>.filterNot(
    predicate: suspend (T) -> Boolean
): Flow<T>

Returns a flow containing only values of the original flow that do not match the given predicate.

filterNotNull

fun <T : Any> Flow<T?>.filterNotNull(): Flow<T>

Returns a flow containing only values of the original flow that are not null.

first

suspend fun <T> Flow<T>.first(): T

The terminal operator that returns the first element emitted by the flow and then cancels flow’s collection. Throws NoSuchElementException if the flow was empty.

suspend fun <T> Flow<T>.first(
    predicate: suspend (T) -> Boolean
): T

The terminal operator that returns the first element emitted by the flow matching the given predicate and then cancels flow’s collection. Throws NoSuchElementException if the flow has not contained elements matching the predicate.

firstOrNull

suspend fun <T> Flow<T>.firstOrNull(): T?

The terminal operator that returns the first element emitted by the flow and then cancels flow’s collection. Returns null if the flow was empty.

suspend fun <T> Flow<T>.firstOrNull(
    predicate: suspend (T) -> Boolean
): T?

The terminal operator that returns the first element emitted by the flow matching the given predicate and then cancels flow’s collection. Returns null if the flow did not contain an element matching the predicate.

flatMapConcat

fun <T, R> Flow<T>.flatMapConcat(
    transform: suspend (value: T) -> Flow<R>
): Flow<R>

Transforms elements emitted by the original flow by applying transform, that returns another flow, and then concatenating and flattening these flows.

flatMapLatest

fun <T, R> Flow<T>.flatMapLatest(
    transform: suspend (value: T) -> Flow<R>
): Flow<R>

Returns a flow that switches to a new flow produced by transform function every time the original flow emits a value. When the original flow emits a new value, the previous flow produced by transform block is cancelled.

flatMapMerge

fun <T, R> Flow<T>.flatMapMerge(
    concurrency: Int = DEFAULT_CONCURRENCY,
    transform: suspend (value: T) -> Flow<R>
): Flow<R>

Transforms elements emitted by the original flow by applying transform, that returns another flow, and then merging and flattening these flows.

flowWith

fun <T, R> Flow<T>.flowWith(
    flowContext: CoroutineContext,
    bufferSize: Int = BUFFERED,
    builder: Flow<T>.() -> Flow<R>
): Flow<R>

The operator that changes the context where all transformations applied to the given flow within a builder are executed. This operator is context preserving and does not affect the context of the preceding and subsequent operations.

fold

suspend fun <T, R> Flow<T>.fold(
    initial: R,
    operation: suspend (acc: R, value: T) -> R
): R

Accumulates value starting with initial value and applying operation current accumulator value and each element

launchIn

fun <T> Flow<T>.launchIn(scope: CoroutineScope): Job

Terminal flow operator that launches the collection of the given flow in the scope. It is a shorthand for scope.launch { flow.collect() }.

map

fun <T, R> Flow<T>.map(
    transform: suspend (value: T) -> R
): Flow<R>

Returns a flow containing the results of applying the given transform function to each value of the original flow.

mapLatest

fun <T, R> Flow<T>.mapLatest(
    transform: suspend (value: T) -> R
): Flow<R>

Returns a flow that emits elements from the original flow transformed by transform function. When the original flow emits a new value, computation of the transform block for previous value is cancelled.

mapNotNull

fun <T, R : Any> Flow<T>.mapNotNull(
    transform: suspend (value: T) -> R?
): Flow<R>

Returns a flow that contains only non-null results of applying the given transform function to each value of the original flow.

onCompletion

fun <T> Flow<T>.onCompletion(
    action: suspend FlowCollector<T>.(cause: Throwable?) -> Unit
): Flow<T>

Returns a flow that invokes the given action after the flow is completed or cancelled, passing the cancellation exception or failure as cause parameter of action.

onEach

fun <T> Flow<T>.onEach(action: suspend (T) -> Unit): Flow<T>

Returns a flow that invokes the given action before each value of the upstream flow is emitted downstream.

onEmpty

fun <T> Flow<T>.onEmpty(
    action: suspend FlowCollector<T>.() -> Unit
): Flow<T>

Invokes the given action when this flow completes without emitting any elements. The receiver of the action is FlowCollector, so onEmpty can emit additional elements. For example:

onStart

fun <T> Flow<T>.onStart(
    action: suspend FlowCollector<T>.() -> Unit
): Flow<T>

Returns a flow that invokes the given action before this flow starts to be collected.

onSubscription

fun <T> SharedFlow<T>.onSubscription(
    action: suspend FlowCollector<T>.() -> Unit
): SharedFlow<T>

Returns a flow that invokes the given action after this shared flow starts to be collected (after the subscription is registered).

produceIn

fun <T> Flow<T>.produceIn(
    scope: CoroutineScope
): ReceiveChannel<T>

Creates a produce coroutine that collects the given flow.

publish

fun <T> Flow<T>.publish(): Flow<T>
fun <T> Flow<T>.publish(bufferSize: Int): Flow<T>

reduce

suspend fun <S, T : S> Flow<T>.reduce(
    operation: suspend (accumulator: S, value: T) -> S
): S

Accumulates value starting with the first element and applying operation to current accumulator value and each element. Throws NoSuchElementException if flow was empty.

replay

fun <T> Flow<T>.replay(): Flow<T>
fun <T> Flow<T>.replay(bufferSize: Int): Flow<T>

retry

fun <T> Flow<T>.retry(
    retries: Int = Int.MAX_VALUE,
    predicate: (Throwable) -> Boolean = { true }
): Flow<T>

retryWhen

fun <T> Flow<T>.retryWhen(
    predicate: suspend FlowCollector<T>.(cause: Throwable, attempt: Long) -> Boolean
): Flow<T>

Retries collection of the given flow when an exception occurs in the upstream flow and the predicate returns true. The predicate also receives an attempt number as parameter, starting from zero on the initial call. This operator is transparent to exceptions that occur in downstream flow and does not retry on exceptions that are thrown to cancel the flow.

fun <T> SharedFlow<T>.retryWhen(
    predicate: suspend FlowCollector<T>.(cause: Throwable, attempt: Long) -> Boolean
): Flow<T>

runningReduce

fun <T> Flow<T>.runningReduce(
    operation: suspend (accumulator: T, value: T) -> T
): Flow<T>

Reduces the given flow with operation, emitting every intermediate result, including initial value. The first element is taken as initial value for operation accumulator. This operator has a sibling with initial value – scan.

sample

fun <T> Flow<T>.sample(periodMillis: Long): Flow<T>

Returns a flow that emits only the latest value emitted by the original flow during the given sampling period.

fun <T> Flow<T>.sample(period: <ERROR CLASS>): Flow<T>

Returns a flow that emits only the latest value emitted by the original flow during the given sampling period.

scan

fun <T, R> Flow<T>.scan(
    initial: R,
    operation: suspend (accumulator: R, value: T) -> R
): Flow<R>

Folds the given flow with operation, emitting every intermediate result, including initial value. Note that initial value should be immutable (or should not be mutated) as it is shared between different collectors. For example:

scanReduce

fun <T> Flow<T>.scanReduce(
    operation: suspend (accumulator: T, value: T) -> T
): Flow<T>

shareIn

fun <T> Flow<T>.shareIn(
    scope: CoroutineScope,
    started: SharingStarted,
    replay: Int = 0
): SharedFlow<T>

Converts a cold Flow into a hot SharedFlow that is started in the given coroutine scope, sharing emissions from a single running instance of the upstream flow with multiple downstream subscribers, and replaying a specified number of replay values to new subscribers. See the SharedFlow documentation for the general concepts of shared flows.

single

suspend fun <T> Flow<T>.single(): T

The terminal operator that awaits for one and only one value to be emitted. Throws NoSuchElementException for empty flow and IllegalStateException for flow that contains more than one element.

singleOrNull

suspend fun <T> Flow<T>.singleOrNull(): T?

The terminal operator that awaits for one and only one value to be emitted. Returns the single value or null, if the flow was empty or emitted more than one value.

stateIn

fun <T> Flow<T>.stateIn(
    scope: CoroutineScope,
    started: SharingStarted,
    initialValue: T
): StateFlow<T>

Converts a cold Flow into a hot StateFlow that is started in the given coroutine scope, sharing the most recently emitted value from a single running instance of the upstream flow with multiple downstream subscribers. See the StateFlow documentation for the general concepts of state flows.

suspend fun <T> Flow<T>.stateIn(
    scope: CoroutineScope
): StateFlow<T>

Starts the upstream flow in a given scope, suspends until the first value is emitted, and returns a hot StateFlow of future emissions, sharing the most recently emitted value from this running instance of the upstream flow with multiple downstream subscribers. See the StateFlow documentation for the general concepts of state flows.

switchMap

fun <T, R> Flow<T>.switchMap(
    transform: suspend (value: T) -> Flow<R>
): Flow<R>

take

fun <T> Flow<T>.take(count: Int): Flow<T>

Returns a flow that contains first count elements. When count elements are consumed, the original flow is cancelled. Throws IllegalArgumentException if count is not positive.

takeWhile

fun <T> Flow<T>.takeWhile(
    predicate: suspend (T) -> Boolean
): Flow<T>

Returns a flow that contains first elements satisfying the given predicate.

toCollection

suspend fun <T, C : MutableCollection<in T>> Flow<T>.toCollection(
    destination: C
): C

Collects given flow into a destination

toList

suspend fun <T> SharedFlow<T>.toList(): List<T>
suspend fun <T> Flow<T>.toList(
    destination: MutableList<T> = ArrayList()
): List<T>

Collects given flow into a destination

toSet

suspend fun <T> SharedFlow<T>.toSet(): Set<T>
suspend fun <T> Flow<T>.toSet(
    destination: MutableSet<T> = LinkedHashSet()
): Set<T>

Collects given flow into a destination

transform

fun <T, R> Flow<T>.transform(
    transform: suspend FlowCollector<R>.(value: T) -> Unit
): Flow<R>

Applies transform function to each value of the given flow.

transformLatest

fun <T, R> Flow<T>.transformLatest(
    transform: suspend FlowCollector<R>.(value: T) -> Unit
): Flow<R>

Returns a flow that produces element by transform function every time the original flow emits a value. When the original flow emits a new value, the previous transform block is cancelled, thus the name transformLatest.

transformWhile

fun <T, R> Flow<T>.transformWhile(
    transform: suspend FlowCollector<R>.(value: T) -> Boolean
): Flow<R>

Applies transform function to each value of the given flow while this function returns true.

withIndex

fun <T> Flow<T>.withIndex(): Flow<IndexedValue<T>>

Returns a flow that wraps each element into IndexedValue, containing value and its index (starting from zero).

zip

fun <T1, T2, R> Flow<T1>.zip(
    other: Flow<T2>,
    transform: suspend (T1, T2) -> R
): Flow<R>

Zips values from the current flow (this) with other flow using provided transform function applied to each pair of values. The resulting flow completes as soon as one of the flows completes and cancel is called on the remaining flow.

Inheritors

MutableStateFlow

interface MutableStateFlow<T> : 
    StateFlow<T>,
    MutableSharedFlow<T>

A mutable StateFlow that provides a setter for value. An instance of MutableStateFlow with the given initial value can be created using MutableStateFlow(value) constructor function.