I don't understand why passing `null` as a second argument to `Map.getOrDefault()` works: ```val gre...

# getting-started

[Ellen Spertus]

I don't understand why passing null as a second argument to Map.getOrDefault() works:

val greekLettersMap: Map<Char, String> = mapOf(
    'a' to "alpha",
    'b' to "beta",
    'g' to "gamma",
)
println(greekLettersMap['a'])
println(greekLettersMap['b'])
println(greekLettersMap.get('g'))
println(greekLettersMap.getOrDefault('c', null))

According to the documentation, this is the signature:

open fun getOrDefault(
    key: K,
    defaultValue: @UnsafeVariance V
): V

Why is null acceptable as the second parameter when it's not part of the non-nullable type Char? Is that what @UnsafeVariance is permitting?

[ephemient]

no

[ephemient]

as Map<K, out V> is covariant in V, Map<K, V> is a Map<K, V?>

[ephemient]

call sites of extension functions are free to choose whichever type variables best suit the call, just like call sites of free functions

[ephemient]

… is what I was going to say, but I just realized you're using getOrDefault() which is a Java default interface method, not the Kotlin extension getOrElse()

[ephemient]

so in this case "no, because of Java interop"

[Ellen Spertus]

I'm happy to switch to getOrElse().

[ephemient]

getOrElse is completely happy to use a supertype for reasons I mentioned before that