Scala's either with tuple as Right

for-comprehension, scala

Solution

Issue seems to be a scala bug https://issues.scala-lang.org/browse/SI-7222. Converting the for comprehension to flatMap/map notation seems to work.

val either: Either[String, (Int, Int)] = Right((1, 2))
either.right.map {
  case (a, b) =>
    a + b
}

either: Either[String,(Int, Int)] = Right((1,2))
res0: Serializable with Product with scala.util.Either[String,Int] = Right(3)

Problem

Suppose I have following code: ``` val either: Either[String, (Int, Int)] = Right((1,2)) for { (a, b) <- either.right } yield a + b ``` When I evaluate it in REPL I get :13: error: constructor cannot be instantiated to expected type; found : (T1, T2) required: scala.util.Either[Nothing,(Double, Double)] (a, b) <- a.right ^ :14: error: not found: value a } yield a + b ^ Why do I have such error? Can't I pattern match on tuple from Either's Right?

Original source