Filter Kotlin collection of pairs so pair content is not null

Question

I am looking for a way to filter a List<Pair<T?, U?>> to a List<Pair<T, U>>: I would like to ignore pairs containing null.

Works, but i need smartcasting, too:

fun <T, U> List<Pair<T?, U?>>.filterAnyNulls() = 
    filter { it.first != null && it.second != null }

Works, but ugly !!, and does not feel idiomatic at all

fun <T, U> List<Pair<T?, U?>>.filterAnyNulls() = mapNotNull {
    if (it.first == null || it.second == null) {
        null
    } else {
        Pair(it.first!!, it.second!!)
    }
}

Any nice solutions? And any more generic solutions? (Maybe even in classes which can be deconstructed, like triples or data classes?)

Answer 1

This solution utilizes destructuring and smart casts and will do what you need without ugly !!:

fun <T, U> List<Pair<T?, U?>>.filterPairs(): List<Pair<T, U>> =
    mapNotNull { (t, u) ->
        if (t == null || u == null) null else t to u
    }