Dequeue

interface ~~Dequeue~~<F, A> Deprecated: The IO datatype and it’s related type classes will disappear in Arrow 0.13.0. All useful operations are offered directly over suspend functions by Arrow Fx Coroutines. https://arrow-kt.io/docs/fx/async/

Dequeue allows peeking and taking values from a Queue, but doesn’t allow offering values to the Queue. You can use Dequeue to restrict certain functions or layers of your applications to only consume values.

import arrow.fx.*
import arrow.fx.typeclasses.*
import arrow.fx.extensions.fx
import kotlin.coroutines.EmptyCoroutineContext

//sampleStart
suspend fun main(args: Array<String>): Unit = IO.fx {
  fun consumeInts(e: Dequeue<ForIO, Int>, max: Int): IOOf<Unit> =
    (0..max).toList().parTraverse(EmptyCoroutineContext) { i ->
      IO.sleep(i * 10.milliseconds).followedBy(
        e.take().effectMap { println("I took $it") }
      )
    }.void()

  val queue = !Queue.unbounded<Int>()
  !consumeInts(queue, 1000).fork()
  !IO.sleep(4.seconds)
}.suspended()
//sampleEnd

See Also

Queue

Dequeue

Functions

peek	Peeks a value from the Queue or semantically blocks until a value becomes available. In contrast to take, peek does not remove the value from the Queue.`abstract fun peek(): Kind<F, A>`
peekAll	Immediately returns all available values in the Queue, without empty’ing the Queue. It returns an emptyList when no values are available.`abstract fun peekAll(): Kind<F,` `List<A>>`
take	Takes and removes a value from the Queue, or semantically blocks until a value becomes available.`abstract fun take(): Kind<F, A>`
takeAll	Immediately returns all available values in the Queue, and empties the Queue. It returns an emptyList when no values are available.`abstract fun takeAll(): Kind<F,` `List<A>>`
tryPeek	Tries to peek a value from the Queue. Returns immediately with either None or a value Some. In contrast to tryTake, tryPeek does not remove the value from the Queue.`abstract fun tryPeek(): Kind<F, Option<A>>`
tryTake	Attempts to take a value from the Queue if one is available, this method is guaranteed not to semantically block. It returns immediately an Option with either None or a value wrapped in Some.`abstract fun tryTake(): Kind<F, Option<A>>`

Inheritors

Queue Lightweight Concurrent Queue for values of A.interface ~~Queue~~<F, A> : QueueOf<F, A>, Dequeue<F, A>, Enqueue<F, A>