Hi Guys! I am wondering is there any generic funct...

# arrow

[VladKopanev]

Hi Guys! I am wondering is there any generic function in arrow that helps turn a bunch of nullable values into a one nullable value given a function e.g. data class constructor, it could be smth like this:

fun <A, B, C, D> fromNullable(a: A?, b: B?, c: C?, f: (A, B, C) -> D): D?

[VladKopanev]

I do understand that it could be done by Option monad comprehension, but maybe there is a way for basic nullable types from kotlin?

[simon.vergauwen]

There is no way of doing this atm, but I actually want to add it to Arrow-Core.

Especially given we’re deprecating Option in 0.11.0.
https://github.com/arrow-kt/arrow-core/issues/120

[simon.vergauwen]

I actually needs this relatively frequent, and end up chaining ?.let which is super ugly.

[simon.vergauwen]

It would great to have your input/suggestions on the ticket if you don’t mind :)

[VladKopanev]

@simon.vergauwen same for me, ?.let just annoys me. I'll give a look at the ticket, tnx!

[streetsofboston]

We wrote a bunch of overloaded let scoping functions for this:

fun <A: Any,B: Any,C: Any,R> let(a: A?, b: B?, c: C?, block: (A, B, C) -> R): R {
    return if (a != null && b != null && c != null) block(a,b,c) else null
}

[simon.vergauwen]

Yes, we need to expose something similar from Arrow IMO, or even Kotlin std.

[VladKopanev]

@streetsofboston I did the same functions in my codebase, but it seems like we could have them on lib level

[VladKopanev]

feels like a common pattern

[streetsofboston]

Maybe it shouldn’t be called let, but guard or something similar 🙂

[VladKopanev]

@simon.vergauwen would you mind if I create a separate ticket for this issue?

[simon.vergauwen]

Not at all!

[VladKopanev]

ok, cool

[simon.vergauwen]

Thanks for the ticket! 👍

[VladKopanev]

Posting the issue here, so anyone who is interested could participate https://github.com/arrow-kt/arrow-core/issues/159