In case you need the index of each element in the constructor of the elements of the array:

Declaration:

var matrix: Array<Array<Obstacle?>>

Instantiation and initialization:

matrix = Array(numRows) { row ->
            Array(numCols) { col ->
                Obstacle(row, col)
            }
         }

You can use private var arrayMap: Array<Array<Obstacle?>> = arrayOf(). Just wrap with as much Array<> as you need.

Not sure if this is what you want, but imagine that Obstacle is a custom class with a field num as below

data class Obstacle(var num: Int){}

A 2D array of the Obstacle object would be as below:

val array: Array<Obstacle?> = arrayOf(Obstacle(123), Obstacle(234))
val arrayOfArray: Array<Array<Obstacle?>> = arrayOf(array)
println(arrayOfArray[0][0]) // would print Obstacle(num=123)
println(arrayOfArray[0][1]) // would print Obstacle(num=234)

So you should be declaring your 2D array as below

val arrayOfArray: Array<Array<Obstacle?>> = arrayOf()