1. Keeping counts of things as mutable state. `Mu...

# advent-of-code

[Nir]

2. Keeping counts of things as mutable state. MutableMap<T, Long> is okay-ish for this, but incrementing feels very awkward

myCounts[something] = myCounts.getOrDefault(something, 0) + numberFound

I've generally found that updating state in maps can be a bit annoying so I do have a general helper function (which I think would be worth having in stdlib tbh)

fun <K, V> MutableMap<K, V>.update(k: K, transform: (V?) -> V) = set(k, transform(get(k)))

So it becomes

myCounts.update(k) { (it ?: 0) + numberFound

But still, end up repeating quite a bit. If there isn't a better way then I may just have a dedicated Counter (a la python) and possibly deal with both things with one stone

[ephemient]

if I had to do it a lot, I'd probably write

class MutableLong(var value: Long)
val myCounts = mutableMapOf<T, MutableLong>()
myCounts.getOrPut(k) { MutableLong(0) }.value += number

as that also avoids repeatedly boxing Long

[ephemient]

but so far in AoC I've usually just restructured the program to use LongArray which ends up both shorter and faster

[Luke]

On JVM with Java 1.8+, your update fonction is basically the MutableMap.compute function ignoring the first argument of the lambda. You can use map.compute(key) { _, value -> (value ?: 0) + numberFound } . You also have a computeIfPresent and computeIfAbsent

[Nir]

yeah but this is basically Java internals at this point no

[Nir]

it's not part of the Kotlin language. But if the underlying data structure already provides that operation, all the more reason to provide something like it.

[ephemient]

kotlin-stdlib is still Java 1.6+ though

[ephemient]

even if you added it to kotlin-stdlib-jdk8, that still excludes common (js and native)… or if you put it in common, that breaks jdk6/7…