Random style question: ```line.mapIndexedNotNull{ ...

# advent-of-code

[Nir]

Random style question:

line.mapIndexedNotNull{ y, c -> if(c == '#') (x to y).toPoint(d) else null }

Or:

line.withIndex().filter { it.value == '#' }.map { (y, _) -> (x to y).toPoint(d) }

[ephemient]

personally: the first one, unless it's really awkward

[ephemient]

Kotlin doesn't (and can't, in general) have Haskell's list fusion optimization, so it does make a difference

[Kroppeb]

The second one has wrong y coordinates I think

[Nir]

why do you think the second has a wrong y coordinate?

[Nir]

@ephemient yeah, that's true, though if line were a sequence instead of an iterable the difference should be pretty minimal no?

[Nir]

if line is an iterable than filter produces a whole new list which isn't great

[ephemient]

well it says list in front so I was not expecting it to be a sequence ;) for sequence, if your type is a primitive, going through the extra stage forces an extra box/unbox, so sometimes the cost is measureable

[Nir]

it says "line" I think, but point taken 🙂 . but yeah good point about unboxing.

[ephemient]

oh I can't read, oops

[Kroppeb]

Sorry, missed the initial withIndex instead of mapWithIndex

[Kroppeb]

I have a extension function for this anyway

[bjonnh]

why don't you filter and then mapIndex ?

[bjonnh]

oh I see you want to keep the index

[bjonnh]

nevermind