tuple_flow_helpers.md

Using Tuple-2 Flow Helpers

Sometimes when processing data through a flow you might want to keep a pair of data together but only care about operating over one part of the pair. Fleam provides mapRight and mapLeft to make this easier and less verbose.

For example, imagine we have a map of people to distances in kilometers.

type Kilometers = Double
val peopleToKilometers: Map[String, Kilometers] = Map(
  "Ryan" -> 1.0,
  "Aniket" -> 2.3,
  "Sobhagya" -> 3.4,
  "Vid" -> 0.0,
  "Michael" -> 4.0,
  "Kender" -> 2.7
)

Now lets also define a function to turn kilometers into miles.

type Miles = Double
val kilometersToMiles: Kilometers => Miles = { kilometers => kilometers * 0.621371 }

We can use fleam's mapRight function to make converting the numbers easier in a flow. This way our function doesn't need to be aware of the tuple and the flow only needs minimal boiler-plate for just working with the right side.

import org.apache.pekko.stream.scaladsl._
import com.nike.fleam.implicits._
import concurrent.Future

val peopleToMiles: Future[Seq[(String, Miles)]] = {
  Source(peopleToKilometers.toList)
    .mapRight(kilometersToMiles)
    .runWith(Sink.seq)
}

Which gives us:

Success(Map(Vid -> 0.0, Kender -> 1.6777017, Ryan -> 0.621371, Aniket -> 1.4291532999999998, Sobhagya -> 2.1126614, Michael -> 2.485484))