Is Arrow having something like zip function for nullable Kotlin variables? Solving this problem: <ht...

# arrow

[Marius Kotsbak]

Is Arrow having something like zip function for nullable Kotlin variables? Solving this problem: https://stackoverflow.com/questions/35513636/multiple-variable-let-in-kotlin

[than_]

it does. It's Nullable.zip 🙂

[Marius Kotsbak]

Ah, I was looking at autocomplete methods on the nullable variable. Maybe that is not allowed to define?

Addet it to SO.

[Youssef Shoaib [MOD]]

It's probably completely valid to define it, but I'm guessing it'll pollute the autocomplete for all Kotlin variables, since anything defined on Any? also accepts Any

[than_]

Not just pollute, there's gonna be no way to distinguish which function to call

val e1: Either<A,B>
val e2: Either<A,B>
e1.zip(e2, ::Pair)

[Youssef Shoaib [MOD]]

Isn't it the case that extension funs are resolved based on the most specific receiver type?, so actually that case should work, but it'll be confusing if you have a nullable either

[than_]

try running this:

import arrow.core.Either
import arrow.core.zip

inline fun <A,B, R> A?.zip(b: B?, f: (A, B) -> R): R? =
    this?.let{ aa -> b?.let{bb -> f(aa,bb)}}

val e1 = Either.Right(1)
val e2 = Either.Left(Unit)

null.zip(2, ::Pair).let(::println)
e1.zip(e2, ::Pair).let(::println)

it's gonna print

null // as expected
(Either.Right(1), Either.Left(kotlin.Unit)) // yikes :D