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

# getting-started

[veiset]

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()

[menegatti]

veiset: unrelated, but do you know that you can do "a" to 1, instead of creating a new Pair?

[diesieben07]

The V in Map is an out parameter, so really the signature is public inline fun <K, V> Map<K, out V>.getOrElse...

[veiset]

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

[diesieben07]

V is inferred to be Any and then you have a Map<K, out Any>, which your map satisfies.

[veiset]

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?

[veiset]

Yup. You do.

[diesieben07]

Yes. Declaration-Site variance is the keyword here.

[veiset]

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