tagless final

DI_tagless.sc

import cats.{Id, Monad}

// domain layer ------------------------------------------------------
case class Movie(id: Int, title: String)

trait MovieRepoSym[F[_]] {
  def getMovie(id: Int): F[Option[Movie]]
}

class MovieService[F[_]: Monad](sym: MovieRepoSym[F]) {
  def getMovie(id: Int): F[Option[Movie]] =
    sym.getMovie(id)
}

// application layer ------------------------------------------------------
import monix.eval.Task

val db = Map[Int, Movie](42 -> Movie(42, "A Movie"))

object TaskInterpreter extends MovieRepoSym[Task] {
  def getMovie(id: Int): Task[Option[Movie]] = Task(db.get(id))
}
val service = new MovieService(TaskInterpreter)
val program = service.getMovie(42)

// runtime (the end of the universe) -------------------------------------
import scala.concurrent.Await
import scala.concurrent.duration._
import monix.execution.Scheduler.Implicits.global

Await.result(program.runToFuture, 1.second)
//Some(Movie(42,A Movie))

// test environment -------------------------------------------------------
object TestInterpreter extends MovieRepoSym[Id] {
  def getMovie(id: Int): Option[Movie] = Option(Movie(-1, "Dummy"))
}
val id1 = new MovieService(TestInterpreter).getMovie(42)
//Some(Movie(-1,Dummy))