Hey! I am trying to understand how the type def of

getOrElse

works.

fun foo(x: String) : () -> String  = { x + "!" }

val map = mapOf(Pair("a", 1), Pair("b", 2))
val result = map.getOrElse("x", foo("kotlin"))

I would expect a type-error here, but it happily returns a String. If I define the type of

result

it works as I would expect. Can someone help me understand the type definition of `orGetElse`:

public inline fun <K, V> Map<K, V>.getOrElse(key: K, defaultValue: () -> V): V = get(key) ?: defaultValue()

veiset: unrelated, but do you know that you can do

"a" to 1

, instead of creating a new

Pair

?

The

V

in

Map

is an

out

parameter, so really the signature is

public inline fun <K, V> Map<K, out V>.getOrElse...

Oh, I didn't know that Edson. That's pretty sweet. Thanks!

V

is inferred to be

Any

and then you have a

Map<K, out Any>

, which your map satisfies.

Oh. That makes sense. How do I see that the signature really is

Map<K, out V>

? Do I have to check the signature of

Map

?

Yes. Declaration-Site variance is the keyword here.

Thanks Take! Perfect, now I understand. Cheers. 😄