ZIO learning - effectfully atomic update like operations / published by https://github.com/dacr/code-examples-manager #a4cfd379-4365-45cb-84df-ab080f94c76a/97f44f63d61d3172286b8e24ff3b9142e668c92c

zio-learning-19-shared-state-refm.sc

// summary : ZIO learning - effectfully atomic update like operations
// keywords : scala, zio, learning, pure-functional, @testable
// publish : gist
// authors : David Crosson
// license : Apache License Version 2.0 (https://www.apache.org/licenses/LICENSE-2.0.txt)
// id : a4cfd379-4365-45cb-84df-ab080f94c76a
// created-on : 2021-04-06T15:32:12+02:00
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala "3.4.2"
//> using dep "dev.zio::zio:2.0.13"
// ---------------------

import zio.*

object Encapsulated extends ZIOAppDefault {

  // Ref[A]             : is a "mutable" cell that contains a reference to an A that may be updated atomically
  // Ref.Synchonized[A] : is a "mutable" cell that contains a reference to an A that may be updated atomically and effectfully!
  val ages  = Map(1 -> 12, 2 -> 42, 3 -> 35, 4 -> 54, 6 -> 17, 7 -> 99)
  val users = ages.keys

  def apiGetAge(userId: Int) = ZIO.fromOption(ages.get(userId))

  def run = {
    for {
      ref <- Ref.Synchronized.make(0)
      _   <- ZIO.foreachPar(users)(id => ref.updateZIO(cur => apiGetAge(id).map(_ + cur)))
      sum <- ref.get
      mean = sum / users.size
      _   <- Console.printLine(s"mean=$mean")
    } yield mean
  }
}

Encapsulated.main(Array.empty)