EitherT leftWiden not available for Nothing error type
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Description
It seems leftWiden is not available for EitherT with type Nothing as the error.
A proposal was to add leftWiden directly into EitherT instead of having it be implicit
EitherT(cats.effect.IO(Either.right[Nothing, Int](1))).leftWiden[String]
results in the following message:
type arguments [String] do not conform to method leftWiden's type parameter bounds [AA >: A]
val res7 = EitherT(cats.effect.IO(Either.right[Nothing, Int](1))).leftWiden[String]
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the shown EitherT example with Nothing as the error type and inspect how the current implicit leftWiden operation is exposed. The work is done when the example compiles with String as the widened error type, without relying on the failing type-parameter bounds.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- scala
- Domain
- backend-api-design
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100