Is it possible to create a generic function which ...

# android

[Ofir Bar]

Is it possible to create a generic function which limits the type T to 2 different objects?

For example, here we limit to type Cat or Dog something like(this is pseudocode):

private fun<T : Cat or Dog> convertToIntArray(objects: List<T>) : IntArray {
    val objectIds = arrayListOf<Int>()
    objects.forEach {
        objectIds.add(it.id)
    }
    return objectIds.toIntArray()
}

// Then pass something like this:
val cats = convertToIntArray(oldListOfCats)
val dogs = convertToIntArray(oldListOfDogs)

[KamilH]

I think you need to make Cat and Dog extend or implement some class/interface (Animal for example) and then you could use where something like that:

private fun<T> convertToIntArray(objects: List<T>) : IntArray where T : Animal {
    val objectIds = arrayListOf<Int>()
    objects.forEach {
        objectIds.add(it.id)
    }
    return objectIds.toIntArray()
}

https://kotlinlang.org/docs/reference/generics.html

[Ofir Bar]

Thank you @KamilH

[BrianZhang]

If this is java, You need a wildcats symbol. fun<? extends Animal>. "Extends" means to implement the Animal Interface here. However, Kotlin has some nice ways to work around this. Check the generic page~