Is there already a more idiomatic way to do this which is at kotlinlang #codingconventions

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Title

d

darkmoon_uk

05/21/2019, 2:11 PM

Is there already a more idiomatic way to do this (which is at least as efficient?):

fun <T,R> Iterable<T>.firstMappedOrNull( mapping: (T)->R? ) : R? {
    for(element in this) {
        mapping(element)?.let { return it }
    }
    return null
}

r

rook

05/21/2019, 2:13 PM

foo.map { /*some transform*/ }.find { it != null }

m

marstran

05/21/2019, 2:22 PM

Using a sequence:

return asSequence()
  .map(mapping)
  .find { it != null }

I think the null check has to be on the result of the call to

mapping

@rook

r

rook

05/21/2019, 2:25 PM

Ah, I didn’t realize that, good catch

y

Yossi Saiada

07/16/2019, 1:04 PM

foo.mapNotNull(mapping).firstOrNull()

d

darkmoon_uk

07/17/2019, 1:11 PM

@Yossi Saiada That is concise but less efficient - in your solution all values will be mapped before the first is picked. @marstran’s solution addresses that requirement with a

Sequence

- where sequence operators generally act like builders, deferring computation of each element until there's an operator that forces the value to resolve e.g.

.toList()

.

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