Hello! I have an immutable state with a map that l...

# arrow

[Sergey Shevtsov]

Hello!
I have an immutable state with a map that looks like:

@Immutable
@optics
data class ViewState(
  val someValue: Map<String, AnotherDataClass>
)

@Immutable
@optics
data class AnotherDataClass(
  val someList: List<String>
)

How can i change multiple values in this map in 1 operation using Arrow?

[dave08]

This is maybe a starter: https://arrow-kt.io/learn/immutable-data/traversal/

[Sergey Shevtsov]

I got something like this:

@Immutable
@optics
data class ViewState(
  val key: SomeKey,
  val someValue: Map<SomeKey, AnotherDataClass>
)

enum class SomeKey { Key1, Key2 }

ViewState.someValue.every(Every.map).modify(state) { value ->
  val newList = when (value.key) {
    Key1 -> listOf(1, 2, 3)
    Key2 -> listOf(4, 5, 6)
  }
  AnotherDataClass.someList.set(value, newList)
}

This is fine? Or is there a better solution here?

[dave08]

You tried optic's copy { ... } method on your ViewState?

[dave08]

https://github.com/arrow-kt/arrow/blob/3d7cb6e5304bb0ebfc8836e59c3cb6dcbd7a1884/ar[…]/optics/arrow-optics/src/commonMain/kotlin/arrow/optics/Copy.kt

[dave08]

There you can modify multiple elements in your data class in a clean way.

[Sergey Shevtsov]

Take a look please. Is it good enough? I only need to change 2 lists for now

private fun ViewState.setValues(list1: List<String>, list2: List<String>): ViewState = copy {
  ViewState.someValue.index(Index.map(), Key1).someList set list1
  ViewState.someValue.index(Index.map(), Key2).someList set list2
}

[dave08]

Yeah, looks ok!

[Sergey Shevtsov]

Thanks for the help! 🤜🤛