why can i do ```val x: List<Int> = listOf(1,...

# getting-started

[LastExceed]

why can i do

val x: List<Int> = listOf(1, 2, 3)
val y: List<Number> = x //works fine

but not

val x: Array<Int> = arrayOf(1, 2, 3)
val y: Array<Number> = x //error: type mismatch

?

[Rick Clephas]

This is due to the generic variance: https://kotlinlang.org/docs/generics.html#variance
List is defined as List<out E> and Array as Array<T>.

In your example list can only return Int elements.
So this allows the cast to Number since every Int is also a Number.

Array however also accepts elements (e.g. in the set function).
Since it expects an Int in these functions you won't be able to cast the array to Number. This is because while all `Int`s are `Number`s not all `Number`s are `Int`s.

[LastExceed]

Array however also accepts elements

i dont understand this part, what does element mean exactly?

[Rick Clephas]

With element I mean an item in the array or list. So in your example 1, 2 and 3 are the elements.

[LastExceed]

but then what is the sentence

Array however also accepts elements

supposed to mean? it kinda implies that lists dont accept elements which makes no sense

[Rick Clephas]

Yeah a List is immutable. So you can't add more elements to it (if you want to add elements to a list you would need a MutableList).
Array however does allow you to update the elements with the set function.

[LastExceed]

oooh thats what you meant. got it ty