Question

I have two functions that are working as expected

1. def getSomething: Promise[JsValue]
2. def getSomethingElse: Promise[JsValue]

Now I want to define a third function (def getAll: Promise[JsValue]) that calls getSomething and then based on the response either return the response or getSomethingElse and append its response to the original.

I currently have getAll defined as follows:

def getAll: Promise[JsValue] = {
  getSomething flatMap { response:JsValue =>
    (response \ "someAttribute").asOpt[String] match {
      case None =>
        val resultPromise = Promise[JsValue]
        resultPromise.redeem(response)
        resultPromise
      case Some(someAttribute) => getSomethingElse map { moreResponse:JsValue =>
        response ++ moreResponse
      }
    }
  }
}

This works but was wondering if there was a shorter way to accomplish the same thing that was more canonical scala?

Answer 1

Got a response from Derek Williams on the cross post on Play Frameworks Google Group.

The only thing I see there that isn’t ideal is pattern matching on Option, instead using map/getOrElse gives you a bit more freedom to compose better. Also, if you aren’t going to use some value, it’s best to not give it a name and instead use _

def getAll: Promise[JsValue] = {
  getSomething flatMap { response =>
    (response \ "someAttribute").asOpt[String] map { _ =>
      getSomethingElse map (response ++ _)
    } getOrElse {
      Promise pure response
    }
  }
}