rougsig / kotlin-flow-extensions

Extensions to the Kotlin Flow library.

kotlin-flow-extensions

Extensions to the Kotlin Flow library.

dependency

Maven

dependencies {
    implementation "com.github.akarnokd:kotlin-flow-extensions:0.0.4"
}

Features

Table of contents

• Hot Flows
  • PublishSubject
  • ReplaySubject
  • BehaviorSubject
• Sources
  • range
  • timer
• Intermediate Flow operators (FlowExtensions)
  • Flow.concatWith
  • Flow.groupBy
  • Flow.parallel
  • Flow.publish
  • Flow.replay
  • Flow.startCollectOn
  • Flow.takeUntil
  • Flow.onBackpressureDrop
  • Flow.flatMapDrop
• ParallelFlow operators (FlowExtensions)
  • ParallelFlow.concatMap
  • ParallelFlow.filter
  • ParallelFlow.map
  • ParallelFlow.reduce
  • ParallelFlow.sequential
  • ParallelFlow.transform
• ConnectableFlow

PublishSubject

Multicasts values to one or more flow collectors in a coordinated fashion, awaiting each collector to be ready to receive the next item or termination.

import hu.akarnokd.kotlin.flow.*

runBlocking {
    
    val publishSubject = PublishSubject<Int>()

    val job = launch(Dispatchers.IO) {
        publishSubject.collect {
            println(it)
        }
        println("Done")
    }
    
    // wait for the collector to arrive
    while (!publishSubject.hasCollectors()) {
        delay(1)
    }

   
    publishSubject.emit(1)
    publishSubject.complete()
   
    job.join()
}

ReplaySubject

Caches and replays some or all items to collectors. Constructors for size-bound, time-bound and both size-and-time bound replays are available. An additional constructor with a TimeUnit -> Long has been defined to allow virtualizing the progression of time for testing purposes

import hu.akarnokd.kotlin.flow.*

runBlocking {
    
    val replaySubject = ReplaySubject<Int>()

    val job = launch(Dispatchers.IO) {
        replaySubject.collect {
            println(it)
        }
        println("Done")
    }
   
    // wait for the collector to arrive
    while (!replaySubject.hasCollectors()) {
        delay(1)
    }

    replaySubject.emit(1)
    replaySubject.emit(2)
    replaySubject.emit(3)
    replaySubject.complete()
   
    job.join()

    replaySubject.collect {
        println(it)
    }
    println("Done 2")
}

BehaviorSubject

Caches the last item received and multicasts it and subsequent items (continuously) to collectors, awaiting each collector to be ready to receive the next item or termination. It is possible to set an initial value to be sent to fresh collectors via a constructor.

import hu.akarnokd.kotlin.flow.*

runBlocking {
    
    val behaviorSubject = BehaviorSubject<Int>()
    behaviorSubject.emit(1)
  
    // OR
    // val behaviorSubject = BehaviorSubject<Int>(1)


    val job = launch(Dispatchers.IO) {
        behaviorSubject.collect {
            println(it)
        }
        println("Done")
    }
   
    // wait for the collector to arrive
    while (!behaviorSubject.hasCollectors()) {
        delay(1)
    }

    behaviorSubject.emit(2)
    behaviorSubject.emit(3)
    behaviorSubject.complete()
   
    job.join()
}

Flow.flatMapDrop

Maps the upstream value into a Flow and relays its items while ignoring further upstream items until the current inner Flow completes.

import hu.akarnokd.kotlin.flow.*

range(1, 10)
.map {
    delay(100)
    it
}
.flatMapDrop {
    range(it * 100, 5)
            .map {
                delay(30)
                it
            }
}
.assertResult(
        100, 101, 102, 103, 104,
        300, 301, 302, 303, 304,
        500, 501, 502, 503, 504,
        700, 701, 702, 703, 704,
        900, 901, 902, 903, 904
)