What would be an idiomatic way to create Either if...

# arrow

[Ivan Brko]

What would be an idiomatic way to create Either if I am not assigning it to a variable so I can't specify its exact type. To be more precise, I am trying to convert a Result to Either. If Result is Ok want to give that value to right, if Results contain a Throwable I set left to sam error.
Code is something like this:

fun <T : Any> Result<T>.toEither(): Either<RequestError, T> =
    fold({ Either.right(it)}, {Either.left(calculateError())})

However, this doesn't compile (although Intellij doesn't show that anything is wrong with the code), as Either.right creates Either<Nothing, T> and Either.left creates Either<T, Nothing>, so neither branching of the fold returns the needed type. Can I create wanted Either here (without having to create it with val, specify its exact type and returning that). I hoped simply doing something like Either<RequestError, T>.right would work, but of course it doesn't 😄

[raulraja]

Try inverting the order of arguments in your fold function

[raulraja]

sorry didn't realized it was fold from Result

[raulraja]

Perhaps it's easier to just use the Boolean operators

[raulraja]

If isSuccess..

[Ivan Brko]

I can do it like that. Is this situation (not having an easy way to create Either in single line) a design choice or something that might be changed in the future? As far as I can see, technically I could do it with Either.cond but I don't know how nicely that would play with Result

[pakoito]

hint the types

[pakoito]

if this is what I think it is, it’s just the kotlin compiler failing to infer the type of two lambdas that converge because they check them in order, and the first one has incomplete types

[pakoito]

fold({ 
val a: Either<RequestError, T> = Either.right(it)
a
}, {Either.left(calculateError())})

[pakoito]

see if that works