Scalaz extensions
FutureEither
FutureEither is a specialised version of scalaz.EitherT[Future, A, B] which allows simple composition of
Future[A \/ B] operations.
Usage
Include the dependency from maven central: com.beamly:beamly-core-scalaz
import scala.concurrent.Future
import beamly.core.scalaz.future.{FutureEither, \?/}
import com.zeebox.core.http.common.HttpStatus.{NotFound, Ok}
import com.zeebox.core.http.server.http.HttpResponse
case class UserNotFound(userId: String)
class Example {
def findFriends(userId: UserId): UserNotFound \?/ Seq[User] = ???
def handleUserNotFound: UserNotFound => HttpResponse[Nothing] = {
userNotFoundError => HttpResponse.failure(NotFound, s"User $userId not found")
}
def friendsResponse(userId: UserId): Future[HttpResponse[Seq[User]]] = {
val response: FutureEither[HttpResponse[Nothing], HttpResponse[Seq[User]]] =
for {
friends <- findFriends(userId) leftMap handleUserNotFound
} yield HttpResponse(Ok, data = Some(friends))
response.union
}
}The steps above when calling friendsResponse are:
- call
findFriendswhich returns either a user not found error or a list of friends - the call to
leftMapmaps the left-hand result (ie:UserNotFound) to a 404HttpResponse - the yield returns the right-hand result which is the list of your friends, but wrapped in a 200
HttpResponse - the entire for-comprehension thus returns
FutureEither[HttpResponse[Nothing], HttpResponse[Seq[User]]] - the
unionmethod flattens theFutureEither[HttpResponse[Nothing], HttpResponse[Seq[User]]]to aFuture[HttpResponse[Seq[User]]]
Converting a regular Future to a FutureEither
def findUser(userId: UserId): Future[Option[User]]
findUser.toEither.leftMap {
case ex: UserNotFoundException =>
UserNotFound(userId)
}findUser.toEither returns FutureEither[Throwable, Option[User]] and the leftMap call simply converts Throwable to UserNotFound.
