Scala Futures vs Kotlin Coroutines comparison

gistfile1.md

Scala with Futures:

import java.util.UUID
import scala.concurrent.Future

trait User {
    def isAdmin: Boolean
    def id: UUID
  }
trait Profile {
  val accessLevel: Int
}

def createUser(user: User): Future[User] = ???
def createProfile(userId: UUID, profile: Profile): Future[Profile] = ???
def createAdminRights(admin: User, accessLevel: Int): Future[Unit] = ???

def create(newUser: User, newProfile: Profile): Future[Unit] = {
    for {
      user <- createUser(newUser)
      profile <- createProfile(user.id, newProfile)
      _ <- if (user.isAdmin) {
        createAdminRights(user, profile.accessLevel)
      } else {
        Future.unit
      }
    } yield ()
  }
  
object Main {
  import scala.concurrent._
  import scala.concurrent.duration._
  
  def main(args: Array[String]): Unit = {
    val user: User = ???
    val profile: Profile = ???
    Await.result(create(user, profile), 10.seconds)
  }
}

Kotlin with Coroutines:

import java.util.*

interface User {
    val isAdmin: Boolean
    val id: UUID
}
interface Profile {
    val accessLevel: Int
}


suspend fun createUser(user: User): User = TODO()
suspend fun createProfile(userId: UUID, profile: Profile): Profile = TODO()
suspend fun createAdminRights(admin: User, accessLevel: Int): Unit = TODO()

suspend fun create(newUser: User, newProfile: Profile) = {
    val user = createUser(newUser)
    val profile = createProfile(user.id, newProfile)
    if (user.isAdmin) {
        createAdminRights(user, profile.accessLevel)
    }
}

object Main {
    fun main(args: Array<String>) = runBlocking {
        val user: User = TODO()
        val profile: Profile = TODO()
        create(user, profile)
    }
}

Scala futures can written in the style of coroutines using async/await.

The newer -Xasync compiler flag, which replaces the traditional macro approach, generalizes to monads other than Future.

And there are various other projects providing/generalizing continuation passing style in different ways. Cats, for example, has a CPS library that would work with Monix.