FlowExt | Kotlinx Coroutines Flow Extensions | Kotlinx Coroutines Flow Extensions. Extensions to the Kotlin Flow library | kotlin-flow-extensions | Coroutines Flow Extensions | Kotlin Flow extensions | kotlin flow extensions | Flow extensions
Kotlinx Coroutines Flow Extensions. Extensions to the Kotlin Flow library. Kotlin Flow extensions. Multiplatform Kotlinx Coroutines Flow Extensions. Multiplatform Extensions to the Kotlin Flow library. Multiplatform Kotlin Flow extensions. RxJS Kotlin Coroutines Flow. RxSwift Kotlin Coroutines Flow. RxJava Kotlin Coroutines Flow. RxJS Kotlin Flow. RxSwift Kotlin Flow. RxJava Kotlin Flow. RxJS Coroutines Flow. RxSwift Coroutines Flow. RxJava Coroutines Flow. Kotlin Flow operators. Coroutines Flow operators.
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android
.jvm
.js
(IR
).wasmJs
.iosArm64
, iosX64
, iosSimulatorArm64
.watchosArm32
, watchosArm64
, watchosX64
, watchosSimulatorArm64
, watchosDeviceArm64
.tvosX64
, tvosSimulatorArm64
, tvosArm64
.macosX64
, macosArm64
.mingwX64
linuxX64
, linuxArm64
.androidNativeArm32
, androidNativeArm64
, androidNativeX86
, androidNativeX64
.Note: This is still a relatively early version of FlowExt, with much more to be desired. I gladly accept PRs, ideas, opinions, or improvements. Thank you! :)
allprojects {
repositories {
...
mavenCentral()
}
}
implementation("io.github.hoc081098:FlowExt:0.8.1-Beta")
allprojects {
repositories {
...
maven(url = "https://s01.oss.sonatype.org/content/repositories/snapshots/")
}
}
dependencies {
implementation("io.github.hoc081098:FlowExt:0.8.2-SNAPSHOT")
}
allprojects {
repositories {
...
maven { url "https://s01.oss.sonatype.org/content/repositories/snapshots/" }
}
}
dependencies {
implementation("io.github.hoc081098:FlowExt:0.8.2-SNAPSHOT")
}
Create
Intermediate operators
bufferCount
combine
cast
castNotNull
castNullable
catchAndReturn
, catchAndResume
chunked
safeCast
concatWith
startWith
flatMapFirst
exhaustMap
flattenFirst
flatMapConcatEager
mapEager
flattenEager
exhaustAll
groupBy
ignoreElements
mapIndexed
mapTo
mapToUnit
mapToResult
mapResultCatching
throwFailure
materialize
dematerialize
raceWith
ambWith
pairwise
repeat
retryWhenWithDelayStrategy
retryWhenWithExponentialBackoff
retryWithExponentialBackoff
scanWith
select
skipUntil
dropUntil
takeUntil
throttleTime
withLatestFrom
zipWithNext
plus
Buffers the source Flow
values until the size hits the maximum bufferSize
given.
Note, chunked
is an alias to bufferCount
.
range(start = 0, count = 10)
.bufferCount(bufferSize = 3)
.collect { println("bufferCount: $it") }
println("---")
range(start = 0, count = 10)
.bufferCount(bufferSize = 3, startBufferEvery = 2)
.collect { println("bufferCount: $it") }
Output:
bufferCount: [0, 1, 2]
bufferCount: [3, 4, 5]
bufferCount: [6, 7, 8]
bufferCount: [9]
---
bufferCount: [0, 1, 2]
bufferCount: [2, 3, 4]
bufferCount: [4, 5, 6]
bufferCount: [6, 7, 8]
bufferCount: [8, 9]
Creates an output Flow
which sequentially emits all values from the first given Flow
and then moves on to the next.
concat(
flow1 = flowOf(1, 2, 3),
flow2 = flowOf(4, 5, 6)
).collect { println("concat: $it") }
Output:
concat: 1
concat: 2
concat: 3
concat: 4
concat: 5
concat: 6
Creates a Flow
that, on collection, calls a Flow
factory to make a Flow
for each new FlowCollector
.
In some circumstances, waiting until the last minute (that is, until collection time)
to generate the Flow
can ensure that collectors receive the freshest data.
var count = 0L
val flow = defer {
delay(count)
flowOf(count++)
}
flow.collect { println("defer: $it") }
println("---")
flow.collect { println("defer: $it") }
println("---")
flow.collect { println("defer: $it") }
Output:
defer: 0
---
defer: 1
---
defer: 2
Creates a cold flow that produces a single value from the given function
.
It calls the function for each new FlowCollector
.
See also flowFromSuspend for the suspend version.
var count = 0L
val flow = flowFromNonSuspend { count++ }
flow.collect { println("flowFromNonSuspend: $it") }
println("---")
flow.collect { println("flowFromNonSuspend: $it") }
println("---")
flow.collect { println("flowFromNonSuspend: $it") }
Output:
flowFromNonSuspend: 0
---
flowFromNonSuspend: 1
---
flowFromNonSuspend: 2
Creates a cold flow that produces a single value from the given function
.
It calls the function for each new FlowCollector
.
See also flowFromNonSuspend for the non-suspend version.
var count = 0L
val flow = flowFromSuspend {
delay(count)
count++
}
flow.collect { println("flowFromSuspend: $it") }
println("---")
flow.collect { println("flowFromSuspend: $it") }
println("---")
flow.collect { println("flowFromSuspend: $it") }
Output:
flowFromSuspend: 0
---
flowFromSuspend: 1
---
flowFromSuspend: 2
Returns a Flow
that emits a 0L
after the initialDelay
and ever-increasing numbers
after each period
of time thereafter.
interval(initialDelay = 100.milliseconds, period = 1.seconds)
.take(5)
.collect { println("interval: $it") }
Output:
interval: 0
interval: 1
interval: 2
interval: 3
interval: 4
Returns a NeverFlow
that never emits any values to the FlowCollector
and never completes.
neverFlow()
.startWith(7)
.collect { println("neverFlow: $it") }
println("Completed!")
Output:
neverFlow: 7
// Never prints "Completed!"
Mirrors the one Flow
in an Iterable
of several Flow
s that first either emits a value
or sends a termination event (error or complete event).
When you pass a number of source Flow
s to race
, it will pass through the emissions
and events of exactly one of these Flow
s: the first one that sends an event to race
,
either by emitting a value or sending an error or complete event.
race
will cancel the emissions and events of all of the other source Flow
s.
race(
flow {
delay(100)
emit(1)
emit(2)
emit(3)
},
flow {
delay(200)
emit(2)
emit(3)
emit(4)
}
).collect { println("race: $it") }
Output:
race: 1
race: 2
race: 3
Creates a Flow
that emits a sequence of numbers within a specified range.
range(start = 0, count = 5)
.collect { println("range: $it") }
Output:
range: 1
range: 2
range: 3
range: 4
Creates a Flow
that will wait for a given duration
, before emitting the value
.
timer(value = Unit, duration = 1.seconds)
.collect { println("timer: $it") }
Output:
// After 1 second
timer: kotlin.Unit
combine
versions for 6 - 12
Flow
s.Catches exceptions in the flow completion, and emits a single item or resumes with another flow.
Similar to
flowOf(1, 2)
.concatWith(flow { throw RuntimeException("original error") })
.catchAndReturn(3)
.collect { v: Int -> println("catchAndReturn: $v") }
println("---")
flowOf(1, 2)
.concatWith(flow { throw RuntimeException("original error") })
.catchAndReturn { e: Throwable -> e.message?.length ?: 0 }
.collect { v: Int -> println("catchAndReturn: $v") }
println("---")
flowOf(1, 2)
.concatWith(flow { throw RuntimeException("original error") })
.catchAndResume(flowOf(3, 4))
.collect { v: Int -> println("catchAndResume: $v") }
println("---")
flowOf(1, 2)
.concatWith(flow { throw RuntimeException("original error") })
.catchAndResume { e: Throwable -> flowOf(e.message?.length ?: 0) }
.collect { v: Int -> println("catchAndResume: $v") }
Output:
catchAndReturn: 1
catchAndReturn: 2
catchAndReturn: 3
---
catchAndReturn: 1
catchAndReturn: 2
catchAndReturn: 14
---
catchAndResume: 1
catchAndResume: 2
catchAndResume: 3
catchAndResume: 4
---
catchAndResume: 1
catchAndResume: 2
catchAndResume: 14
Adapt this Flow
to be a Flow<R>
.
This Flow
is wrapped as a Flow<R>
which checks at run-time that each value event emitted
by this Flow is also an instance of R
.
At the collection time, if this Flow
has any value that is not an instance of R
,
a ClassCastException
will be thrown.
flowOf<Any?>(1, 2, 3)
.cast<Int>()
.collect { v: Int -> println("cast: $v") }
Output:
cast: 1
cast: 2
cast: 3
Adapt this Flow<T?>
to be a Flow<T>
.
At the collection time, if this Flow
has any null
value,
a NullPointerException
will be thrown.
flowOf<Int?>(1, 2, 3)
.castNotNull()
.collect { v: Int -> println("castNotNull: $v") }
Output:
castNotNull: 1
castNotNull: 2
castNotNull: 3
Adapt this Flow<*>
to be a Flow<R?>
.
At the collection time, if this Flow
has any value that is not an instance of R, null will be emitted.
flowOf<Any?>(1, 2, 3, "Kotlin", null)
.safeCast<Int?>()
.collect { v: Int? -> println("safeCast: $v") }
Output:
safeCast: 1
safeCast: 2
safeCast: 3
safeCast: null
safeCast: null
Returns a Flow
that emits the items emitted from the current Flow
, then the next, one after the other, without interleaving them.
Note, plus
is an alias to concatWith
.
flowOf(1, 2, 3)
.concatWith(flowOf(4, 5, 6))
.collect { println("concatWith: $it") }
println("---")
val flow1 = flowOf(1, 2, 3)
val flow2 = flowOf(4, 5, 6)
(flow1 + flow2).collect { println("plus: $it") }
Output:
concatWith: 1
concatWith: 2
concatWith: 3
concatWith: 4
concatWith: 5
concatWith: 6
---
plus: 1
plus: 2
plus: 3
plus: 4
plus: 5
plus: 6
Returns a Flow
that emits a specified item (or many items) before it begins to emit items emitted by the current Flow
.
flowOf(1, 2, 3)
.startWith(0)
.collect { println("startWith: $i") }
Output:
startWith: 0
startWith: 1
startWith: 2
startWith: 3
Projects each source value to a Flow
which is merged in the output Flow
only if the previous projected Flow
has completed.
If value is received while there is some projected Flow
sequence being merged, it will simply be ignored.
This method is a shortcut for map(transform).flattenFirst()
.
range(1, 5)
.onEach { delay(100) }
.flatMapFirst { timer(it, 130) }
.collect { println("flatMapFirst: $it") }
Output:
flatMapFirst: 1
flatMapFirst: 3
flatMapFirst: 5
Converts a higher-order Flow
into a first-order Flow
by dropping inner Flow
while the previous inner Flow
has not yet completed.
range(1, 5)
.onEach { delay(100) }
.map { timer(it, 130) }
.flattenFirst()
.collect { println("flattenFirst: $it") }
Output:
flattenFirst: 1
flattenFirst: 3
flattenFirst: 5
Groups the items emitted by the current Flow
according to a specified criterion,
and emits these grouped items as GroupedFlow
s.
range(1, 10)
.groupBy { it % 2 }
.flatMapMerge { groupedFlow ->
groupedFlow
.map { groupedFlow.key to it }
}
.collect { println("groupBy: $it") }
Output:
groupBy: (1, 1)
groupBy: (0, 2)
groupBy: (1, 3)
groupBy: (0, 4)
groupBy: (1, 5)
groupBy: (0, 6)
groupBy: (1, 7)
groupBy: (0, 8)
groupBy: (1, 9)
groupBy: (0, 10)
Ignores all elements emitted by the source Flow
, only passes calls of complete
or error
.
flowOf("you", "talking", "to", "me")
.ignoreElements()
.materialize()
.collect { println("ignoreElements: $it") }
Output:
ignoreElements: Event.Complete
Transforms elements emitted by the original Flow
by applying transform
, that returns another flow
,
and then merging and flattening these flows.
This operator calls transform
sequentially and then concatenates the resulting flows with a concurrency
limit on the number of concurrently collected flows.
It is a shortcut for map(transform).flattenConcatEager(concurrency)
.
range(1, 5)
.onEach { delay(100) }
.flatMapConcatEager(concurrency = 2) { v ->
timer(v, 130)
.onStart { println("flatMapConcatEager: onStart $v") }
.onCompletion { println("flatMapConcatEager: onCompletion $v") }
}
.collect { println("flatMapConcatEager: $it") }
Output:
flatMapConcatEager: onStart 1
flatMapConcatEager: onStart 2
flatMapConcatEager: 1
flatMapConcatEager: onCompletion 1
flatMapConcatEager: onStart 3
flatMapConcatEager: 2
flatMapConcatEager: onCompletion 2
flatMapConcatEager: onStart 4
flatMapConcatEager: 3
flatMapConcatEager: onCompletion 3
flatMapConcatEager: onStart 5
flatMapConcatEager: 4
flatMapConcatEager: onCompletion 4
flatMapConcatEager: 5
flatMapConcatEager: onCompletion 5
Returns a flow containing the results of applying the given transform
function
to each value and its index in the original flow.
range(1, 3)
.mapIndexed { index, value -> index to value }
.collect { println("mapIndexed: $it") }
Output:
mapIndexed: (0, 1)
mapIndexed: (1, 2)
mapIndexed: (2, 3)
Emits the given constant value on the output Flow
every time the source Flow
emits a value.
range(1, 3)
.mapTo("Value")
.collect { println("mapTo: $it") }
Output:
mapTo: Value
mapTo: Value
mapTo: Value
Emits kotlin.Unit
value on the output Flow
every time the source Flow
emits a value.
range(1, 3)
.mapToUnit()
.collect { println("mapToUnit: $it") }
Output:
mapToUnit: kotlin.Unit
mapToUnit: kotlin.Unit
mapToUnit: kotlin.Unit
Maps values in the Flow
to successful results (aka Result.success
),
and catches and wraps any exception into a failure result (aka Result.failure
).
flowOf(1, 2)
.concatWith(flow { throw RuntimeException("error") })
.mapToResult()
.collect { result: Result<Int> -> println("mapToResult: $result") }
Output:
mapToResult: Success(1)
mapToResult: Success(2)
mapToResult: Failure(java.lang.RuntimeException: error)
Maps a Flow
of Result
s to a Flow
of a mapped Result
s.
Any exception thrown by the transform
function is caught,
and emitted as a failure result] (aka Result.failure
) to the resulting flow.
flowOf(1, 2)
.concatWith(flow { throw RuntimeException("original error") })
.mapToResult()
.mapResultCatching {
if (it == 1) throw RuntimeException("another error")
else (it * 2).toString()
}
.collect { result: Result<String> -> println("mapResultCatching: $result") }
Output:
mapResultCatching: Failure(java.lang.RuntimeException: another error)
mapResultCatching: Success(4)
mapResultCatching: Failure(java.lang.RuntimeException: original error)
Maps a Flow
of Result
s to a Flow
of values from successful results.
Failure results are re-thrown as exceptions.
try {
flowOf(1, 2)
.concatWith(flow { throw RuntimeException("original error") })
.mapToResult()
.throwFailure()
.collect { v: Int -> println("throwFailure: $v") }
} catch (e: Throwable) {
println("throwFailure: caught $e")
}
Output:
throwFailure: 1
throwFailure: 2
throwFailure: caught java.lang.RuntimeException: original error
Represents all of the notifications from the source Flow
as value
emissions marked with their original types within Event
objects.
flowOf(1, 2, 3)
.materialize()
.collect { println("materialize: $it") }
Output:
materialize: Event.Value(1)
materialize: Event.Value(2)
materialize: Event.Value(3)
materialize: Event.Complete
Converts a Flow
of Event
objects into the emissions that they represent.
flowOf(Event.Value(1), Event.Value(2), Event.Value(3))
.dematerialize()
.collect { println("dematerialize: $it") }
Output:
dematerialize: 1
dematerialize: 2
dematerialize: 3
Mirrors the current Flow
or the other Flow
s provided of which the first either emits a value
or sends a termination event (error or complete event).
flow {
delay(100)
emit(1)
emit(2)
emit(3)
}.raceWith(
flow {
delay(200)
emit(2)
emit(3)
emit(4)
}
).collect { println("raceWith: $it") }
Output:
raceWith: 1
raceWith: 2
raceWith: 3
Groups pairs of consecutive emissions together and emits them as a pair.
Emits the (n)th
and (n-1)th
events as a pair.
The first value won't be emitted until the second one arrives.
Note, zipWithNext
is an alias to pairwise
.
range(0, 4)
.pairwise()
.collect { println("pairwise: $it") }
println("---")
range(0, 4)
.zipWithNext { a, b -> "$a -> $b" }
.collect { println("zipWithNext: $it") }
Output:
pairwise: (0, 1)
pairwise: (1, 2)
pairwise: (2, 3)
---
zipWithNext: 0 -> 1
zipWithNext: 1 -> 2
zipWithNext: 2 -> 3
Returns a Flow
that will recollect to the source stream when the source stream completes.
flowFromSuspend {
println("Start collecting...")
Random
.nextInt(0..3)
.also { println("Emit: $it") }
}
.repeat(
delay = 1.seconds,
count = 10
)
.filter { it == 2 }
.take(1)
.collect { println("repeat: $it") }
Output:
Start collecting...
Emit: 1
Start collecting...
Emit: 3
Start collecting...
Emit: 1
Start collecting...
Emit: 0
Start collecting...
Emit: 1
Start collecting...
Emit: 3
Start collecting...
Emit: 2
repeat: 2
Retries collection of the given flow when an exception occurs in the upstream flow and the
predicate
returns true. The predicate also receives an attempt
number as parameter,
starting from zero on the initial call. When predicate
returns true, the next retries will be
delayed after a duration computed by DelayStrategy.nextDelay
.
var count = -1
flowFromSuspend {
++count
println("Call count=$count")
when (count) {
0 -> throw MyException(message = "Will retry...", cause = null)
1 -> "Result: count=$count"
else -> error("Unexpected: count=$count")
}
}
.retryWhenWithDelayStrategy(
strategy = DelayStrategy.FixedTimeDelayStrategy(duration = 200.milliseconds),
predicate = { cause, attempt -> cause is MyException && attempt < 1 }
)
.collect { println("retryWhenWithDelayStrategy: $it") }
Output:
Call count=0
Call count=1
retryWhenWithDelayStrategy: Result: count=1
Retries collection of the given flow with exponential backoff delay strategy
when an exception occurs in the upstream flow and the predicate
returns true. When predicate
returns true,
the next retries will be delayed after a duration computed by DelayStrategy.ExponentialBackoffDelayStrategy
.
var count = -1
flowFromSuspend {
++count
println("Call count=$count")
when (count) {
0 -> throw MyException(message = "Will retry...", cause = null)
1 -> "Result: count=$count"
else -> error("Unexpected: count=$count")
}
}
.retryWhenWithExponentialBackoff(
initialDelay = 500.milliseconds,
factor = 2.0,
) { cause, attempt -> cause is MyException && attempt < 1 }
.collect { println("retryWhenWithExponentialBackoff: $it") }
Output:
Call count=0
Call count=1
retryWhenWithExponentialBackoff: Result: count=1
Retries collection of the given flow with exponential backoff delay strategy
when an exception occurs in the upstream flow and the predicate
returns true. When predicate
returns true,
the next retries will be delayed after a duration computed by DelayStrategy.ExponentialBackoffDelayStrategy
.
var count = -1
flowFromSuspend {
++count
println("Call count=$count")
when (count) {
0 -> throw MyException(message = "Will retry...", cause = null)
1 -> "Result: count=$count"
else -> error("Unexpected: count=$count")
}
}
.retryWithExponentialBackoff(
maxAttempt = 2,
initialDelay = 500.milliseconds,
factor = 2.0,
) { it is MyException }
.collect { println("retryWithExponentialBackoff: $it") }
Output:
Call count=0
Call count=1
retryWithExponentialBackoff: Result: count=1
Folds the given flow with [operation], emitting every intermediate result, including the initial value supplied by [initialSupplier] at the collection time.
This is a variant of scan
that the initial value is lazily supplied,
which is useful when the initial value is expensive to create
or depends on a logic that should be executed at the collection time (lazy semantics).
var count = 0
val mutex = Mutex()
suspend fun calculateInitialValue(): Int {
println("calculateInitialValue")
delay(1000)
return mutex.withLock { count++ }
}
flowOf(1, 2, 3)
.scanWith(::calculateInitialValue) { acc, e -> acc + e }
.collect { println("scanWith[1]: $it") }
flowOf(1, 2, 3)
.scanWith(::calculateInitialValue) { acc, e -> acc + e }
.collect { println("scanWith[2]: $it") }
Output:
calculateInitialValue
scanWith[1]: 0
scanWith[1]: 1
scanWith[1]: 3
scanWith[1]: 6
calculateInitialValue
scanWith[2]: 1
scanWith[2]: 2
scanWith[2]: 4
scanWith[2]: 7
Inspirited by NgRx memoized selector.
Selectors are pure functions used for obtaining slices of a Flow of state.
FlowExt
provides a few helper functions for optimizing this selection.
data class UiState(
val items: List<String> = emptyList(),
val term: String? = null,
val isLoading: Boolean = false,
val error: Throwable? = null
)
flow {
println("select: emit 1")
emit(UiState())
println("select: emit 2")
emit(
UiState(
items = listOf("a", "b", "c"),
term = "a",
isLoading = true,
error = Throwable("error")
)
)
println("select: emit 3")
emit(
UiState(
items = listOf("a", "b", "c"),
term = "a",
isLoading = false,
error = Throwable("error")
)
)
println("select: emit 4")
emit(
UiState(
items = listOf("a", "b", "c"),
term = "b",
isLoading = false,
error = Throwable("error")
)
)
}
.select(
selector1 = { it.items },
selector2 = { it.term },
projector = { items, term ->
term?.let { v ->
items.filter { it.contains(v, ignoreCase = true) }
}
}
)
.collect { println("select: $it") }
Output:
select: emit 1
select: null
select: emit 2
select: [a]
select: emit 3
select: emit 4
select: [b]
Returns a Flow
that skips items emitted by the source Flow
until a second Flow
emits a value or completes.
flowOf(1, 2, 3)
.onEach { delay(100) }
.skipUntil(timer(Unit, 150))
.collect { println("skipUntil: $it") }
Output:
skipUntil: 2
skipUntil: 3
Emits the values emitted by the source Flow
until a notifier Flow
emits a value or completes.
range(0, 5)
.onEach { delay(100) }
.takeUntil(timer(Unit, 270.milliseconds))
.collect { println("takeUntil: $it") }
Output:
takeUntil: 0
takeUntil: 1
Returns a Flow
that emits a value from the source Flow
, then ignores subsequent source values
for a duration determined by durationSelector
, then repeats this process for the next source value.
(1..10)
.asFlow()
.onEach { delay(200) }
.throttleTime(500)
.collect { println("throttleTime: $it") }
Output:
throttleTime: 1
throttleTime: 4
throttleTime: 7
throttleTime: 10
Merges two Flow
s into one Flow
by combining each value from self with the latest value from the second Flow
, if any.
Values emitted by self before the second Flow
has emitted any values will be omitted.
range(0, 5)
.onEach { delay(100) }
.withLatestFrom(
range(0, 10)
.onEach { delay(70) }
)
.collect { println("withLatestFrom: $it") }
Output:
withLatestFrom: (0, 0)
withLatestFrom: (1, 1)
withLatestFrom: (2, 3)
withLatestFrom: (3, 4)
withLatestFrom: (4, 6)
... and more, please check out Docs 0.x/Docs snapshot.
MIT License
Copyright (c) 2021-2024 Petrus Nguyễn Thái Học