Conceptual question here. I have a class which contains a list. Whenever the size of the list is 1, ...

# getting-started

[Joshua Hansen]

Conceptual question here. I have a class which contains a list. Whenever the size of the list is 1, I want certain functions to be used, and when it's greater than 1, I want alternative functions (which serve the same purpose but do something a bit different) to be used. (it's a Java swing app in kotlin so lots of gui stuff). What sort of structure should I use to keep this organized?

[Chris Lee]

One option:

when(list.size()) {
  1 -> doSingletonThing()
  else -> doOtherThings() // should 0 be a special case?
}

[Joshua Hansen]

Yeah that works for one function call, but I don't want a bunch of when blocks all over the place.

[Chris Lee]

place it in the class itself, or an extension function as appropriate.

[ephemient]

interface DoThings {
    fun doThingA()
    fun doThingB()
}
class SingleDoThings(val item: T) { override ... }
class MultiDoThings(val items: List<T>) { override ... }
fun DoThings(items: List<T>): DoThings =
    items.singleOrNull()?.let { SingleDoThings(it) }
        ?: MultiDoThings(items)

[Kirill Grouchnikov]

Why overcomplicate instead of using a simple if/else?

[Stephan Schröder]

assuming your list is immutable once it is used to initialise the instance, you could use a sealed class/interface:

sealed class SomeThing {
    abstract fun doSomething()
    
    private data class Single(private val item:String): SomeThing() {
        override fun doSomething() {
            println("single item: $item")
        }
    }
    private data class Multi(private val moreThanOneItem: List<String>): SomeThing() {
        override fun doSomething() {
            println("multiple items: $moreThanOneItem")
        }
    }
    
    companion object {
        fun new(items: List<String>): SomeThing = when(items.size) {
            0 -> error("can't instanciate a SomeThing with an empty list")
            1 -> SomeThing.Single(items.single())
            else -> SomeThing.Multi(items)
        }
    }
}

here on Kotlin Playground: https://pl.kotl.in/bv-Rj9FgG