scala-commons

Common utilities we use in our Scala projects

FutureOr

Motivation

We have a lot of experience building Reactive applications in Scala, so we work with Futures a lot, specifically when interacting with third-party APIs and non-blocking web services. We also try to gracefully handle success and failure, and we've found that Scalactic's Or does a great job in that regard. Consequently, we often have to execute and compose several calls where the return type is Future[Good Or Bad]. Out of the box, this doesn't compose very gracefully. So we made a FutureOr.

FutureOr is a simple wrapper over the type Future[T Or One[E]]. It provides some basic monadic functions and helpers to make working with Future[T Or One[E]] much easier. Scalactic provides a nice type alias ErrorMessage to use for E to indicate errors, but we usually end up constructing our own error objects to make it easier to manage internationalization and API error statuses.

Examples

Simple composition of services returning a Future[T Or One[E]]

for {
  int1 <- FutureOr(service1.call())
  int2 <- FutureOr(service2.call())
} yield {
  int1 + int2
}

From a sequence of Future[T Or One[E]], create a future sequence and accumulate all of the Bad paths

val a: Future[Int Or One[E]] = serviceA.call();
val b: Future[Int Or One[E]] = serviceB.call();
val c: Future[Int Or One[E]] = serviceC.call();

val ints: Seq[Future[Int Or Every[E]]] = FutureOr.sequence(Seq(a, b, c))