Is there a better way to write `listOfStuff.asSequ...

# getting-started

[Mark]

Is there a better way to write listOfStuff.asSequence().mapNotNull { fromStuffToSomethingOrNull(it) }.firstOrNull()

[Andrew]

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]

The asSequence() is there to avoid mapping all the items unnecessarily.

[molikuner]

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 }

[Mark]

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() 😉

[Dico]

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

[molikuner]

Nice!

[Mark]

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]

Then rewrite it to be clearer, it's peanuts

[Dico]

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.

[Dico]

block(i)?.let { return it } perhaps

[Mark]

But now it’s less clear than asSequence().mapNotNull(block).firstOrNull()

[Dico]

I don't think subjective discussions are helpful