Hello people, is there a way to “merge” 2 validated? E.g. given two

Validated<A, B>

, if they were

Either

I would do, for example

either {
  val a = eitherA.bind()
  val b = eitherB.bind()
  Combine(a, b)
}

What’s the right way to do it with

Validated

? Either with the

either

block or any other solution 🙂

You would normally use the

zip

extension for this but you'd need to provide some way of merging

A

in case both were invalid. Usually this is covered by using

ValidatedNel<A, B>

(a typealias for

Validated<NonEmptyList<A>, B>

)

Thank you for the answer. Could you please provide a real example, considering two

Validated<String, Int>

? 🙂

How would you want to merge the two error Strings?

Let’s concatenate them

Regarding that, with Arrow 1.2.x onwards,

Validated

is going to be deprecated, and removed from Arrow 2.0.0 to simplify this.

Oh, I see! So I’ll just use Either?

For

ValidatedNel

it's relatively simple to use

.validNel()

and

.invalidNel()

to construct your values much like you would

.valid()

and

.invalid()

. Once you have two values you can join them using

a.zip(b) { validA, validB -> doSomethingWith(validA, validB) }

Ok. Thank you so much!

With

Validated<A, B>

you need to provide an additional argument to zip of a

Semigroup<A>

(which is effectively just a function

A.(A) -> A

like

String::plus

) With a custom combine to comma-delimit errors you can have

lateinit var a: Validated<String, Int>
lateinit var b: Validated<String, Int>

fun String.combine(other: String) = "$this, $other"

a.zip(String::combine, b) { validA, validB -> validA + validB }

I see! Thanks again!