What would be the equivalent in Java of

Array<IntArray>

? I'm trying to store a 2D matrix of ints/floats in a compact way, would this Array of IntArrays be the way to go? Would that be equivalent to

int[][]

?

If you want to be equivalent, yes that's what this is. However, if accesses to this structure are performance sensitive, you might want to consider a 1-dimensional int array instead (using

i * width + j

indexing to map to 2D). This avoids pointer indirections

yeah, I think I misunderstood how Java lays out

int[][]

in memory - it's not a one continuous chunk of memory, it's array of pointers to arrays with continous memory?

Yes exactly, Java and Kotlin have the same capabilities in this respect, you have to manually handle your 1D array if you want contiguous memory

Just saying, you can very easily create a

@JvmInline value class 2DIntArray

that under the hood uses a normal

IntArray

and lays out the 2d matrix in a continuous block of memory so that it's still efficient but all the indexing for getting and setting are hidden away in the value class

Of course the smart indexing needs to be abstracted away

Yeah I'm just saying that a value class will make that invisible to any consumer of the array

just a little hint on the side: you could write an extension for the get-operator function on

IntArray

(or some wrapper class if you prefer) that accepts 2 parameters. Of course this would require you to know the "width" of your matrix, but it could look something like this:

operator fun IntArray.get(x: Int, y: Int) = get(y * width + x)

That way you could call

my2DArray[x, y]