Is there a `List<T?> -> List<T>?` m...

# getting-started

[min]

Is there a List<T?> -> List<T>? method (or something similar) in the standard library? Almost like requireNoNulls, except I want a function that doesn’t throw.

[Vivek]

filterNotNull() will give you List<T>

if you really want List<T>? then you can do something like:

fun <T> List<T?>.toNonNullListOrNull(): List<T>? =
    mapNotNull { it ?: return null }

[ephemient]

just map, no need for mapNotNull

[fishy]

You could also do

fun <T> List<T?>.toNonNullListOrNull(): List<T>? = @Suppress("UNCHECKED_CAST") (takeIf { null !in it } as? List<T>?)

which isn't as clean because of the unchecked cast but it doesn't require allocating an entirely new list

[ephemient]

it is also much more unsafe. the list could change to include a null after, and keeping the same list instance would propagate it to the non-null typed list