dependency injection sample with ZIO

di_with_zio.sc

import scalaz.zio.{DefaultRuntime, IO, ZIO}

// domain layer -----------------------------------------------------------
sealed trait AppError
case object NoValue extends AppError

case class Movie(id: Int, title: String)

trait MovieRepo {
  def getMovie(id: Int): IO[AppError, Movie]
}

// application layer ----------------------------------------------
val db = Map[Int, Movie](42 -> Movie(42, "A Movie"))
object MovieRepoImpl extends MovieRepo {
  def getMovie(id: Int): IO[AppError, Movie] =
    IO.fromEither(db.get(id).toRight(NoValue))
}

trait Env {
  val movieRepo: MovieRepo
}
object Env extends Env {
  val movieRepo = MovieRepoImpl
}

object MovieService {
  def getMovie(id: Int): ZIO[Env, AppError, Movie] =
    ZIO.environment[Env] >>= (_.movieRepo.getMovie(id))
}
val program: ZIO[Env, AppError, Movie] = MovieService.getMovie(42)

// runtime layer -------------------------------------------------
new DefaultRuntime {}.unsafeRunSync(program.provide(Env))

// testing layer -------------------------------------------------
import cats.syntax.either._
new DefaultRuntime {}.unsafeRunSync(program.provide(new Env {
  val movieRepo = _ => IO.fromEither(NoValue.asLeft)
}))