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More operators (#1236)
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* Scan and emitAll operators
* Flow.first operators family (without firstOrNull and firstOrDefault support)
* More migrations

Fixes #1094
Fixes #1078
Fixes #1244
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qwwdfsad committed Jun 6, 2019
1 parent d15d8d6 commit d5478b6
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Showing 9 changed files with 315 additions and 13 deletions.
Original file line number Diff line number Diff line change
Expand Up @@ -822,10 +822,13 @@ public final class kotlinx/coroutines/flow/FlowKt {
public static final fun distinctUntilChangedBy (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
public static final fun drop (Lkotlinx/coroutines/flow/Flow;I)Lkotlinx/coroutines/flow/Flow;
public static final fun dropWhile (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;
public static final fun emitAll (Lkotlinx/coroutines/flow/FlowCollector;Lkotlinx/coroutines/flow/Flow;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public static final fun emptyFlow ()Lkotlinx/coroutines/flow/Flow;
public static final fun filter (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;
public static final fun filterNot (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;
public static final fun filterNotNull (Lkotlinx/coroutines/flow/Flow;)Lkotlinx/coroutines/flow/Flow;
public static final fun first (Lkotlinx/coroutines/flow/Flow;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public static final fun first (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public static final fun flatMapConcat (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;
public static final fun flatMapMerge (Lkotlinx/coroutines/flow/Flow;ILkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;
public static synthetic fun flatMapMerge$default (Lkotlinx/coroutines/flow/Flow;ILkotlin/jvm/functions/Function2;ILjava/lang/Object;)Lkotlinx/coroutines/flow/Flow;
Expand Down Expand Up @@ -853,6 +856,8 @@ public final class kotlinx/coroutines/flow/FlowKt {
public static final fun retry (Lkotlinx/coroutines/flow/Flow;ILkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
public static synthetic fun retry$default (Lkotlinx/coroutines/flow/Flow;ILkotlin/jvm/functions/Function1;ILjava/lang/Object;)Lkotlinx/coroutines/flow/Flow;
public static final fun sample (Lkotlinx/coroutines/flow/Flow;J)Lkotlinx/coroutines/flow/Flow;
public static final fun scan (Lkotlinx/coroutines/flow/Flow;Ljava/lang/Object;Lkotlin/jvm/functions/Function3;)Lkotlinx/coroutines/flow/Flow;
public static final fun scanReduce (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function3;)Lkotlinx/coroutines/flow/Flow;
public static final fun single (Lkotlinx/coroutines/flow/Flow;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public static final fun singleOrNull (Lkotlinx/coroutines/flow/Flow;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
public static final fun switchMap (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;
Expand All @@ -872,13 +877,17 @@ public final class kotlinx/coroutines/flow/MigrationKt {
public static final fun BehaviourSubject ()Ljava/lang/Object;
public static final fun PublishSubject ()Ljava/lang/Object;
public static final fun ReplaySubject ()Ljava/lang/Object;
public static final fun compose (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
public static final fun concatMap (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
public static final fun flatMap (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/flow/Flow;
public static final fun flatten (Lkotlinx/coroutines/flow/Flow;)Lkotlinx/coroutines/flow/Flow;
public static final fun forEach (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function2;)V
public static final fun merge (Lkotlinx/coroutines/flow/Flow;)Lkotlinx/coroutines/flow/Flow;
public static final fun observeOn (Lkotlinx/coroutines/flow/Flow;Lkotlin/coroutines/CoroutineContext;)Lkotlinx/coroutines/flow/Flow;
public static final fun onErrorResume (Lkotlinx/coroutines/flow/Flow;Lkotlinx/coroutines/flow/Flow;)Lkotlinx/coroutines/flow/Flow;
public static final fun publishOn (Lkotlinx/coroutines/flow/Flow;Lkotlin/coroutines/CoroutineContext;)Lkotlinx/coroutines/flow/Flow;
public static final fun scanFold (Lkotlinx/coroutines/flow/Flow;Ljava/lang/Object;Lkotlin/jvm/functions/Function3;)Lkotlinx/coroutines/flow/Flow;
public static final fun skip (Lkotlinx/coroutines/flow/Flow;I)Lkotlinx/coroutines/flow/Flow;
public static final fun subscribe (Lkotlinx/coroutines/flow/Flow;)V
public static final fun subscribe (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function1;)V
public static final fun subscribe (Lkotlinx/coroutines/flow/Flow;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function1;)V
Expand Down
53 changes: 53 additions & 0 deletions kotlinx-coroutines-core/common/src/flow/Migration.kt
Original file line number Diff line number Diff line change
Expand Up @@ -193,3 +193,56 @@ public fun <T> Flow<Flow<T>>.merge(): Flow<T> = error("Should not be called")
replaceWith = ReplaceWith("flattenConcat()")
)
public fun <T> Flow<Flow<T>>.flatten(): Flow<T> = error("Should not be called")

/**
* Kotlin has a built-in generic mechanism for making chained calls.
* If you wish to write something like
* ```
* myFlow.compose(MyFlowExtensions.ignoreErrors()).collect { ... }
* ```
* you can replace it with
*
* ```
* myFlow.let(MyFlowExtensions.ignoreErrors()).collect { ... }
* ```
*
* @suppress
*/
@Deprecated(
level = DeprecationLevel.ERROR,
message = "Kotlin analogue of compose is 'let'",
replaceWith = ReplaceWith("let(transformer)")
)
public fun <T, R> Flow<T>.compose(transformer: Flow<T>.() -> Flow<R>): Flow<R> = error("Should not be called")

/**
* @suppress
*/
@Deprecated(
level = DeprecationLevel.ERROR,
message = "Kotlin analogue of 'skip' is 'drop'",
replaceWith = ReplaceWith("drop(count)")
)
public fun <T> Flow<T>.skip(count: Int): Flow<T> = error("Should not be called")

/**
* Flow extension to iterate over elements is [collect].
* Foreach wasn't introduced deliberately to avoid confusion.
* Flow is not a collection, iteration over it may be not idempotent
* and can *launch* computations with side-effects.
* This behaviour is not reflected in [forEach] name.
* @suppress
*/
@Deprecated(
level = DeprecationLevel.ERROR,
message = "Flow analogue of 'forEach' is 'collect'",
replaceWith = ReplaceWith("collect(block)")
)
public fun <T> Flow<T>.forEach(action: suspend (value: T) -> Unit): Unit = error("Should not be called")

@Deprecated(
level = DeprecationLevel.ERROR,
message = "Flow has less verbose 'scan' shortcut",
replaceWith = ReplaceWith("scan(initial, operation)")
)
public fun <T, R> Flow<T>.scanFold(initial: R, @BuilderInference operation: suspend (accumulator: R, value: T) -> R): Flow<R> = error("Should not be called")
4 changes: 1 addition & 3 deletions kotlinx-coroutines-core/common/src/flow/operators/Errors.kt
Original file line number Diff line number Diff line change
Expand Up @@ -27,9 +27,7 @@ public fun <T> Flow<T>.onErrorCollect(
predicate: ExceptionPredicate = ALWAYS_TRUE
): Flow<T> = collectSafely { e ->
if (!predicate(e)) throw e
fallback.collect { value ->
emit(value)
}
emitAll(fallback)
}

/**
Expand Down
10 changes: 2 additions & 8 deletions kotlinx-coroutines-core/common/src/flow/operators/Merge.kt
Original file line number Diff line number Diff line change
Expand Up @@ -80,11 +80,7 @@ public fun <T, R> Flow<T>.flatMapMerge(
*/
@FlowPreview
public fun <T> Flow<Flow<T>>.flattenConcat(): Flow<T> = flow {
collect { value ->
value.collect { innerValue ->
emit(innerValue)
}
}
collect { value -> emitAll(value) }
}

/**
Expand Down Expand Up @@ -137,9 +133,7 @@ public fun <T, R> Flow<T>.switchMap(transform: suspend (value: T) -> Flow<R>): F
previousFlow?.join()
// Undispatched to have better user experience in case of synchronous flows
previousFlow = launch(start = CoroutineStart.UNDISPATCHED) {
transform(value).collect { innerValue ->
downstream.emit(innerValue)
}
downstream.emitAll(transform(value))
}
}
}
Expand Down
45 changes: 45 additions & 0 deletions kotlinx-coroutines-core/common/src/flow/operators/Transform.kt
Original file line number Diff line number Diff line change
Expand Up @@ -4,10 +4,12 @@

@file:JvmMultifileClass
@file:JvmName("FlowKt")
@file:Suppress("UNCHECKED_CAST")

package kotlinx.coroutines.flow

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.internal.NULL
import kotlin.jvm.*
import kotlinx.coroutines.flow.unsafeFlow as flow

Expand Down Expand Up @@ -97,3 +99,46 @@ public fun <T> Flow<T>.onEach(action: suspend (T) -> Unit): Flow<T> = flow {
emit(value)
}
}

/**
* 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:
* ```
* flowOf(1, 2, 3).accumulate(emptyList<Int>()) { acc, value -> acc + value }.toList()
* ```
* will produce `[], [1], [1, 2], [1, 2, 3]]`.
*/
@FlowPreview
public fun <T, R> Flow<T>.scan(initial: R, @BuilderInference operation: suspend (accumulator: R, value: T) -> R): Flow<R> = flow {
var accumulator: R = initial
emit(accumulator)
collect { value ->
accumulator = operation(accumulator, value)
emit(accumulator)
}
}

/**
* 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].
*
* For example:
* ```
* flowOf(1, 2, 3, 4).scan { (v1, v2) -> v1 + v2 }.toList()
* ```
* will produce `[1, 3, 6, 10]`
*/
@FlowPreview
public fun <T> Flow<T>.scanReduce(operation: suspend (accumulator: T, value: T) -> T): Flow<T> = flow {
var accumulator: Any? = NULL
collect { value ->
accumulator = if (accumulator === NULL) {
value
} else {
operation(accumulator as T, value)
}
emit(accumulator as T)
}
}
6 changes: 6 additions & 0 deletions kotlinx-coroutines-core/common/src/flow/terminal/Collect.kt
Original file line number Diff line number Diff line change
Expand Up @@ -32,3 +32,9 @@ public suspend inline fun <T> Flow<T>.collect(crossinline action: suspend (value
collect(object : FlowCollector<T> {
override suspend fun emit(value: T) = action(value)
})

/**
* Collects all the values from the given [flow] and emits them to the collector.
* Shortcut for `flow.collect { value -> emit(value) }`.
*/
public suspend inline fun <T> FlowCollector<T>.emitAll(flow: Flow<T>) = flow.collect(this)
47 changes: 45 additions & 2 deletions kotlinx-coroutines-core/common/src/flow/terminal/Reduce.kt
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@

@file:JvmMultifileClass
@file:JvmName("FlowKt")
@file:Suppress("UNCHECKED_CAST")

package kotlinx.coroutines.flow

Expand Down Expand Up @@ -50,7 +51,7 @@ public suspend inline fun <T, R> Flow<T>.fold(
}

/**
* Terminal operator, that awaits for one and only one value to be published.
* The terminal operator, that awaits for one and only one value to be published.
* Throws [NoSuchElementException] for empty flow and [IllegalStateException] for flow
* that contains more than one element.
*/
Expand All @@ -68,7 +69,7 @@ public suspend fun <T> Flow<T>.single(): T {
}

/**
* Terminal operator, that awaits for one and only one value to be published.
* The terminal operator, that awaits for one and only one value to be published.
* Throws [IllegalStateException] for flow that contains more than one element.
*/
@FlowPreview
Expand All @@ -81,3 +82,45 @@ public suspend fun <T: Any> Flow<T>.singleOrNull(): T? {

return result
}

/**
* 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.
*/
@FlowPreview
public suspend fun <T> Flow<T>.first(): T {
var result: Any? = NULL
try {
collect { value ->
result = value
throw AbortFlowException()
}
} catch (e: AbortFlowException) {
// Do nothing
}

if (result === NULL) throw NoSuchElementException("Expected at least one element")
return result as 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].
*/
@FlowPreview
public suspend fun <T> Flow<T>.first(predicate: suspend (T) -> Boolean): T {
var result: Any? = NULL
try {
collect { value ->
if (predicate(value)) {
result = value
throw AbortFlowException()
}
}
} catch (e: AbortFlowException) {
// Do nothing
}

if (result === NULL) throw NoSuchElementException("Expected at least one element matching the predicate $predicate")
return result as T
}
68 changes: 68 additions & 0 deletions kotlinx-coroutines-core/common/test/flow/operators/ScanTest.kt
Original file line number Diff line number Diff line change
@@ -0,0 +1,68 @@
/*
* Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
*/

package kotlinx.coroutines.flow

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
import kotlin.test.*

class ScanTest : TestBase() {
@Test
fun testScan() = runTest {
val flow = flowOf(1, 2, 3, 4, 5)
val result = flow.scanReduce { acc, v -> acc + v }.toList()
assertEquals(listOf(1, 3, 6, 10, 15), result)
}

@Test
fun testScanWithInitial() = runTest {
val flow = flowOf(1, 2, 3)
val result = flow.scan(emptyList<Int>()) { acc, value -> acc + value }.toList()
assertEquals(listOf(emptyList(), listOf(1), listOf(1, 2), listOf(1, 2, 3)), result)
}

@Test
fun testNulls() = runTest {
val flow = flowOf(null, 2, null, null, null, 5)
val result = flow.scanReduce { acc, v -> if (v == null) acc else (if (acc == null) v else acc + v) }.toList()
assertEquals(listOf(null, 2, 2, 2, 2, 7), result)
}

@Test
fun testEmptyFlow() = runTest {
val result = emptyFlow<Int>().scanReduce { _, _ -> 1 }.toList()
assertTrue(result.isEmpty())
}

@Test
fun testErrorCancelsUpstream() = runTest {
expect(1)
val latch = Channel<Unit>()
val flow = flow {
coroutineScope {
launch {
latch.send(Unit)
hang { expect(3) }
}
emit(1)
emit(2)
}
}.scanReduce { _, value ->
expect(value) // 2
latch.receive()
throw TestException()
}.onErrorCollect(emptyFlow())

assertEquals(1, flow.single())
finish(4)
}

public operator fun <T> Collection<T>.plus(element: T): List<T> {
val result = ArrayList<T>(size + 1)
result.addAll(this)
result.add(element)
return result
}
}
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