monix.reactive.internal.operators.SwitchIfEmptyObservable.scala Maven / Gradle / Ivy
/*
* Copyright (c) 2014-2020 by The Monix Project Developers.
* See the project homepage at: https://monix.io
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package monix.reactive.internal.operators
import monix.execution.cancelables.OrderedCancelable
import monix.execution.{Ack, Cancelable}
import monix.reactive.Observable
import monix.reactive.observers.Subscriber
import scala.concurrent.Future
private[reactive] final class SwitchIfEmptyObservable[+A](source: Observable[A], backup: Observable[A])
extends Observable[A] {
override def unsafeSubscribeFn(out: Subscriber[A]): Cancelable = {
val cancelable = OrderedCancelable()
val mainSub = source.unsafeSubscribeFn(new Subscriber[A] {
implicit val scheduler = out.scheduler
private[this] var isEmpty = true
def onNext(elem: A): Future[Ack] = {
if (isEmpty) isEmpty = false
out.onNext(elem)
}
def onComplete(): Unit = {
// If the source was empty, switch to the backup.
if (isEmpty)
cancelable.orderedUpdate(backup.unsafeSubscribeFn(out), 2)
else
out.onComplete()
}
def onError(ex: Throwable): Unit =
out.onError(ex)
})
cancelable.orderedUpdate(mainSub, 1)
}
}