How to best implement a pattern where I want to compute a va kotlinlang #getting-started

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Title

d

David Kubecka

03/09/2023, 1:26 PM

How to best implement a pattern where I want to compute a value for each element in a collection and return those element+value pairs where the value is not null)? Currently, I have simply this

someCollection.map { it to someExpensiveComputation(it) }.filter { it.second != null }

which works but the return type is

List<T, R?>

and I of course want

List<T, R>

.

e

ephemient

03/09/2023, 1:27 PM

someCollection.mapNotNull {
    val result = someExpensiveComputation(it) ?: return@mapNotNull null
    it to result
}

you could golf that down to

someCollection.mapNotNull { someExpensiveComputation(it)?.let(it::to) }

but I don't think it's clearer

d

David Kubecka

03/09/2023, 1:31 PM

Ah, I hate those early returns 🙂 Especially from lambdas

e

ephemient

03/09/2023, 1:32 PM

well you could write

if (result != null) it to result else null

or the equivalent

?.let

if you wanted, I just prefer the early return to the additional nested scope

d

David Kubecka

03/09/2023, 1:36 PM

Well, I probably prefer your second solution, although I would just use the infix

to

(have to invent an alias for the inner

it

, though). Btw it didn't occur to me that it can be used this way in its prefix variant but of course it makes sense.

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