Is there a better way to write `listOfStuff asSequence mapNo kotlinlang #getting-started

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Title

Mark

02/15/2020, 5:56 AM

Is there a better way to write

listOfStuff.asSequence().mapNotNull { fromStuffToSomethingOrNull(it) }.firstOrNull()

Andrew

02/15/2020, 6:20 AM

Probably not, depending how its used the asSequence part may not be needed, usually for lazy evaluation of lists. Since its doing firstOrNull its using lazy evaluation to get only the first item which might defeat the purpose.

Mark

02/15/2020, 6:53 AM

The

asSequence()

is there to avoid mapping all the items unnecessarily.

☝️ 2

molikuner

02/15/2020, 11:53 AM

I would at least factor it out to make the intend clear:

inline fun <T, R : Any> List<T>.firstMappedNotNull(block: (T) -> R?): R? = asSequence().mapNotNull(block).firstOrNull()

Also I come up with an other implementation, but I definitely prefer yours, because it’s easier to read and understand.

inline fun <T, R : Any> List<T>.firstMappedNotNull(block: (T) -> R?): R? = forEach { block(it)?.also { return it } }.let { null }

👍 1

Mark

02/15/2020, 1:17 PM

And can apply to any iterable

inline fun <T, R: Any> Iterable<T>.firstMappedOrNull(noinline block: (T) -> R?): R? = asSequence().mapNotNull(block).firstOrNull()

Bonus points for naming it

firstMapNotNullOrNull()

😉

😂 1

👍🏻 2

Dico

02/16/2020, 8:58 PM

for (i in list) return block(i) ?: continue
return null

👍 1

molikuner

02/16/2020, 9:03 PM

Nice!

Mark

02/17/2020, 3:32 AM

It’s clever, but I don’t think as readable because

return block(i) ?: continue

is confusing. You have to work out that

block(i) ?: continue

will be evaluated first and so potentially avoid the return.

Dico

02/17/2020, 11:21 AM

Then rewrite it to be clearer, it's peanuts

You can start by puttimg the expression after the return in parentheses, and you can then move the return into a .let {} on the following line, or expand the if block and make a variable.

block(i)?.let { return it }

perhaps

Mark

02/17/2020, 12:24 PM

But now it’s less clear than

asSequence().mapNotNull(block).firstOrNull()

Dico

02/18/2020, 12:17 AM

I don't think subjective discussions are helpful

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