ZIO learning - structured services - horizontal composition / published by https://github.com/dacr/code-examples-manager #e3518fe7-c997-4684-8eff-6074a7056521/212a46c79d773e82f9a2beaaa089868f3ff8d7b3

zio-learning-26-structured-services-2-horizontal-composition.sc

// summary : ZIO learning - structured services - horizontal composition
// keywords : scala, zio, learning, services, pure-functional, @testable
// publish : gist
// authors : Rock the JVM
// license : Apache License Version 2.0 (https://www.apache.org/licenses/LICENSE-2.0.txt)
// id : e3518fe7-c997-4684-8eff-6074a7056521
// created-on : 2021-05-03T18:04:46+02:00
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// Highly inspired from Structuring Services in Scala with ZIO and ZLayer : https://www.youtube.com/watch?v=PaogLRrYo64
// And lately updated or Scala3 & ZIO2

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

import zio.*

// ----------------------------------------------------------------------------------------
case class User(name: String, email: String)

// ----------------------------------------------------------------------------------------
// This is the classical service pattern used within ZIO, with the standard naming scheme

// Service definition
trait UserEmailer:
  def notify(user: User, message: String): Task[Unit]

object UserEmailer:

  class UserEmailerImpl() extends UserEmailer:
    override def notify(user: User, message: String): Task[Unit] =
      ZIO.attempt(println(s"[User emailer] Sending '$message' to ${user.email}'"))

  val live: URLayer[Any, UserEmailer] = ZLayer.succeed(UserEmailerImpl())

  // Front-facing API - helper function
  def notify(user: User, message: String): RIO[UserEmailer, Unit] =
    ZIO.serviceWithZIO(_.notify(user, message))

// ----------------------------------------------------------------------------------------
trait UserDb:
  def insert(user: User): Task[Unit]

object UserDb:
  class UserDbImpl extends UserDb:
    override def insert(user: User) =
      ZIO.attempt(println(s"[Database] insert into public.user value ('${user.email}')"))

  val live = ZLayer.succeed(UserDbImpl())

  def insert(user: User): RIO[UserDb, Unit] = {
    ZIO.serviceWithZIO(_.insert(user))
  }

// ----------------------------------------------------------------------------------------

object Encapsulated extends ZIOAppDefault:

  val david   = User("david", "[email protected]")
  val message = "Welcome to this site !"

  val layers = ZLayer.make[UserDb & UserEmailer](
    UserDb.live,
    UserEmailer.live
  )

  val logic =
    UserEmailer
      .notify(david, message)     // the kind of effect
      .provideLayer(layers) // provide the input for that effect

  override def run = logic

Encapsulated.main(Array.empty)