Setting nested Options to Some(value)

[oripwk]

Hi,

Given a nested chain of Options, is there a way to coerce the most inner one to Some?

The current operator .each allows traversing Options, but acts like map:

import com.softwaremill.quicklens._

case class C(d: Option[Int])
case class B(c: Option[C])
case class A(b: Option[B])

val a = A(b = None)

a.modify(_.b.each.c.each.d.each).setTo(3)  //  res0: A = A(None)

(the result is A(None), but how can we achieve a A(Some(B(Some(C(Some(3))))))?)

It could be useful if there were some operator (say, all) which can act as follows:

a.modify(_.b.all.c.all.d.all).setTo(3) //  res0: A = A(Some(B(Some(C(Some(3))))))

[adamw]

I'm afraid this is very option-chain-specific. Firstly, you wouldn't be able to use .modify, as there need not be a value. Secondly, if e.g. B had any other fields, there's nowhere to get their values from.

[oripwk]

What about a variation of at(idx: Int) which doesn't throw IndexOutOfBoundsException, and instead enlarges the sequence so accommodate the new index? Such a method could also be adapted to Options if we look at them as sequences if length 1.

[adamw]

But what would you put in the indicies in between? Also, how would you initialize an "empty" object which would be added to the sequence?

[oripwk]

Maybe a type class Zeroable[A] with default implementations for all the primitives?

A completely alternative solution would be a withHead[A](a: A) which can work for all sequences (including Option, Either, etc.)

[adamw]

Maybe Zeroable would work ... but I have the feeling that this takes the .each syntax a bit too far. Wouldn't, in such situations, just writing code in .setTo with the appropriate new instance creation logic be sufficient?

[oripwk]

Yeah, on a second thought, there's no much difference between .setTo and my suggestion.

I guess you're right :)