zio.stream.SubscriptionRef.scala Maven / Gradle / Ivy
/*
* Copyright 2017-2020 John A. De Goes and the ZIO Contributors
*
* 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 zio.stream
import zio._
/**
* A `SubscriptionRef[A]` contains a `RefM` with a value of type `A` and a
* `ZStream` that can be subscribed to in order to receive the current value as
* well as all changes to the value.
*/
final class SubscriptionRef[A] private (val ref: RefM[A], val changes: Stream[Nothing, A])
object SubscriptionRef {
/**
* Creates a new `SubscriptionRef` with the specified value.
*/
def make[A](a: A): UIO[SubscriptionRef[A]] =
for {
ref <- RefM.make(a)
hub <- Hub.unbounded[A]
changes = ZStream.unwrapManaged {
ZManaged {
ref.modify { a =>
ZIO.succeedNow(a).zipWith(hub.subscribe.zio) { case (a, (finalizer, queue)) =>
(finalizer, ZStream(a) ++ ZStream.fromQueue(queue))
} <*> ZIO.succeedNow(a)
}.uninterruptible
}
}
} yield new SubscriptionRef(ref.tapInput(hub.publish), changes)
}