Is there a simple functional way to receive a non-...

# announcements

[Uziel Sulkies]

Is there a simple functional way to receive a non-nullable values map?

[Shawn]

I don’t think filterNot will do what you want it to

[Shawn]

compiler can’t smartcast to non-null

[Shawn]

also, you may want to project V as V : Any

[streetsofboston]

No short way, bu maybe like this:
this.filterNot { it.value == null }.map { it as Entry<K,V> } (not sure if Entry is the correct name)

[streetsofboston]

^^^ I’m not even sure that will work….(don’t have IDE in front of me now :-)

[streetsofboston]

This will work, but it will be an unsafe cast 🙂 :
this.filterNot { it.value == null } as Map<K,V>

[Kroppeb]

Just put it into an extension function and call it a day

[Uziel Sulkies]

It is an extension function we're trying to write. It is possible to do it this way. But is there a shorter way?

[streetsofboston]

I think just an unsafe cast would suffice…

fun <K, V : Any> Map<K,V?>.filterNotNull(): Map<K,V> = 
    filter { it.value != null } as Map<K,V>

[Shawn A]

Can't you just use https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/map-not-null.html?

[Shawn]

I mean, no, not just mapNotNull

[Shawn]

you’d need something a little more involved

[Shawn]

fun <K : Any, V : Any> Map<K, V?>.filterNullValues(): Map<K, V> {
  return mapNotNull { it.value?.let { value -> it.key to value } }.toMap()
}

[Shawn]

since mapNotNull returns List<R>

[Shawn]

and not a Map<K, V>

[Shawn A]

Sorry, yes that is what I was getting it. Should have provided an example thanks 🙂

[Shawn]

my point really being that going the mapNotNull route involves different tradeoffs, mostly just more iteration over your collection