I’m surprised there is not something for this in the standard lib. Is this okay or maybe remove inli...

# codereview

[Mark]

I’m surprised there is not something for this in the standard lib. Is this okay or maybe remove inline/reified?

inline fun <reified K, V> Map<out K?, V>.filterKeyNotNull(): Map<K, V> =
    mapNotNull { (key, value) -> if (key != null) key to value else null }.toMap()

[Milan Hruban]

why not use
map.filterKeys { it != null }

[Mark]

It returns type `Map<K?, V>`:

fun <K, V> Map<out K, V>.filterKeys(predicate: (K) -> Boolean): Map<K, V>

It could be cast like this:

fun <K, V> Map<out K?, V>.filterKeyNotNull(): Map<K, V> =
    filterKeys { it != null } as Map<K, V>

[Ivan Pavlov]

I have 3 years experience and I've never used maps with nullable keys. If it is not in standard library probably it is really rare use case and it's just not worth to add such function