Getting Value of Either

scala either
Kevin Meredith picture Kevin Meredith · Oct 21, 2013 · Viewed 26.1k times · Source

Besides using match, is there an Option-like way to getOrElse the actual content of the Right or Left value?

scala> val x: Either[String,Int] = Right(5)
scala> val a: String = x match { 
                                case Right(x) => x.toString
                                case Left(x) => "left" 
                       }
a: String = 5

Answer

Nicolas Rinaudo picture Nicolas Rinaudo · Oct 21, 2013

I don't particularly like Either and as a result I'm not terribly familiar with it, but I believe you're looking for projections: either.left.getOrElse or either.right.getOrElse.

Note that projections can be used in for-comprehensions as well. This is an example straight from the documentation:

def interactWithDB(x: Query): Either[Exception, Result] =
  try {
    Right(getResultFromDatabase(x))
  } catch {
    case ex => Left(ex)
  }

// this will only be executed if interactWithDB returns a Right
val report =
  for (r <- interactWithDB(someQuery).right) yield generateReport(r)
if (report.isRight)
  send(report)
else
  log("report not generated, reason was " + report.left.get)

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