ZIO learning - transactions / published by https://github.com/dacr/code-examples-manager #382b643a-6998-4726-82e5-9d8080f5ac26/9cc238c98997b0713c3890195d010ca7066b71f9

zio-learning-22-transactions.sc

// summary : ZIO learning - transactions
// keywords : scala, zio, learning, pure-functional, transactions, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : 382b643a-6998-4726-82e5-9d8080f5ac26
// created-on : 2021-11-06T08:14:16Z
// 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"
// ---------------------

/*
 inspired from https://zio.dev/datatypes/stm/stm
 */

import zio.*
import zio.stm.*
import java.io.IOException

object Encapsulated extends ZIOAppDefault {

  def transferMoney(from: TRef[Long], to: TRef[Long], amount: Long): STM[String, (Long, Long)] =
    for {
      senderBalance   <- from.get
      _               <- if (senderBalance < amount) STM.fail("Not enough money") else STM.unit
      _               <- from.update(existing => existing - amount)
      _               <- to.update(existing => existing + amount)
      senderBalance   <- from.get
      receiverBalance <- to.get
    } yield (senderBalance, receiverBalance)

  val app: ZIO[Any, IOException | String, (Long, Long)] = for {
    senderAccount   <- STM.atomically(TRef.make(1000L))
    receiverAccount <- STM.atomically(TRef.make(0L))
    result          <- STM.atomically(transferMoney(senderAccount, receiverAccount, 420L))
    _               <- Console.printLine(result)
  } yield result

  def run = app
}

Encapsulated.main(Array.empty)