CODEWITHSUNDEEP
scalafunctoreitherscala-cats
Michael
Michael

Reputation: 42110

How to resolve this ambiguity while mapping my Either type?

Suppose I've got two types IntResult and StringResult:

import cats._
import cats.data._
import cats.implicits._

scala> case class MyError(msg: String)
defined class MyError

scala> type Result[A] = Either[NonEmptyList[MyError], A]
defined type alias Result

scala> type StringResult = Result[String]
defined type alias StringResult

scala> type IntResult = Result[Int]
defined type alias IntResult

Now I would like to convert IntResult to StringResult using map:

scala> val good1: IntResult = 10.asRight
good1: IntResult = Right(10)

scala> good1 map (_.toString)
<console>:26: error: type mismatch;
found   : good1.type (with underlying type IntResult)
required: ?{def map: ?}
Note that implicit conversions are not applicable because they are ambiguous:
both method catsSyntaxEither in trait EitherSyntax of type [A, B](eab:Either[A,B]) cats.syntax.EitherOps[A,B]
and method toFunctorOps in trait ToFunctorOps of type [F[_], A](target: F[A])(implicit tc: cats.Functor[F])cats.Functor.Ops[F,A]
are possible conversion functions from good1.type to ?{def map: ?}
   good1 map (_.toString)

How to resolve this ambiguity ?

Upvotes: 1

Views: 473

Answers (1)

Oscar Boykin
Oscar Boykin

Reputation: 1974

The simple approach is to use the projections, so you do:

good1.right.map(_.toString)

It's not awesome, but it works. I don't know a way to import so that the functor is not conflicting with the either enrichment (if you need both).

Of course, you could just import cats.syntax.either._ but that won't get you the Functor.

Upvotes: 1

Related Questions