I have a `List lt Pair lt A B gt gt ` Is there an easy way t kotlinlang #announcements

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Title

pavel

10/31/2019, 9:29 PM

I have a

List<Pair<A,B?>>

Is there an easy way to filter out all where

second==null

and make the type be

List<Pair<A,B>>

karelpeeters

10/31/2019, 9:35 PM

Not, you'll have to cast it.

bezrukov

10/31/2019, 9:35 PM

You can try mapNotNull - convert

Pair<A,B?>

Pair<A,B>?

karelpeeters

10/31/2019, 9:35 PM

How to express this is still an open question for contracts: https://github.com/Kotlin/KEEP/blob/master/proposals/kotlin-contracts.md#open-questions

pavel

10/31/2019, 9:37 PM

Thanks

bezrukov

10/31/2019, 9:37 PM

Something like

list.mapNotNull{if (it.second != null) it.first to it.second else null}

pavel

10/31/2019, 9:41 PM

nope, that didn’t work. The inferred type is still

List<Pair<A,B?>>

karelpeeters

10/31/2019, 9:45 PM

You need an intermediate variable, something like

list.mapNotNull {
    val second = it.second
    if (second == null) null else it.first to second
}

bezrukov

10/31/2019, 9:48 PM

list.mapNotNull { (first, second) -> second?.let { first to second } }

➕ 1

pavel

10/31/2019, 9:54 PM

ooo, nice

thank you

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