Using cats-effect's MapRef, concurrent

ConcurrencyMapRef.scala

//> using scala 3.3
//> using dep org.typelevel::cats-effect:3.5.4

import cats.syntax.all.*
import cats.effect.{IO, IOApp}
import cats.effect.std.MapRef

object ConcurrencyMapRef extends IOApp.Simple:

  private val concurrencySample =
    for
      mr <- MapRef.ofSingleImmutableMap[IO, Int, String]()
      _ <- (1 to 20).map{ k =>
          mr.setKeyValue(k, k.toString)
        }.toList.parSequence // Will run 20 puts in parallel
      _ <- (1 to 20).map { k =>
          mr(k).get.flatMap:
            case None => IO.raiseError(new NoSuchElementException(s"Not found value for key $k, this is actually impossible"))
            case Some(v) => IO.println(s"Found value $v for key $k")
        }.toList.parSequence // Will run 20 gets in parallel
    yield ()

  override val run = concurrencySample