Can you dynamically specify a list of choice items?

[Andrew Smith]

In the following example from the documentation, choiceItem objects are specified as static constructor parameters to the choiceItems class.

My question is, is it possible to pass a dynamically created list of choiceItem objects (literally a sequence or list of choiceItem) to a choiceItems constructor? How can I build a dynamic list of choiceItems?

I used map to create a sequence of choiceItem instances, but I can't pass it to the choiceItems constructor as it gets a compiler error.

Example Of Static Item Choices:

// Conditional item of overflow menu:
sectionBlock(
  text = md"Test 2",
  accessory = overflow(
    action_id = SlackActionId("-"),
    options = choiceItems(
      choiceItem( text = pt"test-menu-item 1", value = "1" ),
      choiceItem( text = pt"test-menu-item 2", value = "2" ),
      optionally( someUserParam > 0 ) ( choiceItem( text = pt"conditional-menu-item 3", value = "3" ) )
    )
  )
)

[Abdulla Abdurakhmanov]

Hey,

The reason you (probably) receive a compiler error, that you trying to use choiceItems with Seq[] of choiceItem directly. However choiceItems expects a lazy-computed list of items (to be able to use optional/conditional code as in your example).

So it is something like this:

choiceItems(
  Seq(
       (
                        () => choiceItem( text = pt"test-menu-item 1", value = "1" )
       ),
       (
                        () => choiceItem( text = pt"test-menu-item 2", value = "2" )
       )
    ):_*
)

Yet, it is cumbersome and I don't recommend it in case you just need a list of choice items, and you can use NonEmptyList directly instead of choiceItems:

              sectionBlock(
                text = md"Test 2",
                accessory = overflow(
                  action_id = SlackActionId("-"),
                  options = NonEmptyList.fromListUnsafe(
                    List(
                        choiceItem( text = pt"test-menu-item 1", value = "1" )
                    )
                  )
                )
              )

fromListUnsafe - now this is important to understand, you can't have an empty list of choices, and this will throw an exception in that case. Look at https://typelevel.org/cats/datatypes/nel.html for details.

[Abdulla Abdurakhmanov]

To clarify, if you have at least one static choice, it is better to use NonEmptyList with it and avoid fromListUnsafe construction if possible.

[Abdulla Abdurakhmanov]

And the most safer option would be this:

sectionBlock(
                text = md"Test 2",
                accessory =
                  // Our dynamic list data
                  List(
                    choiceItem( text = pt"test-menu-item 1", value = "1" ),
                    choiceItem( text = pt"test-menu-item 1", value = "1" )
                  ) match {
                    case head :: tail =>
                      // Yay, we have at least on choice
                      Some(
                        overflow(
                          action_id = SlackActionId("-"),
                          options = NonEmptyList(head, tail)
                        )
                      )
                    case _ => {
                      // Fallback, we have no data to show as options, so we don't use overflow at all
                      None
                    }
                  }
              )

Hope this helps. Let me know if something isn't clear.

[Abdulla Abdurakhmanov]

To avoid confusion with this behaviour, I made some changes in 3.0.2 that provide an ability to use choiceItems (and similar construction) with just any Iterable. I'll release it soon.

[Andrew Smith]

Thanks so much!