Resizeable two-dimensional array in Kotlin

Question

I want to know how to make a resizeable two-dimensional array in Kotlin.

C++ example: vector< vector<int> > my_vector

What I've tried: var seqList: List<List<Int>> = ArrayList<ArrayList<Int>>()

but I'm getting an error when using seqList.add()

error: unresolved reference: add

I have read some questions regarding 2d arrays in Kotlin at stackoverflow, but they are about not-resizeable arrays or are outdated

Answer 1

Kotlin has separate List and MutableList interfaces, as explained here, for example. ArrayList is a MutableList, you just have to save it as a MutableList variable in order to be able to access methods that mutate it:

val seqList: MutableList<MutableList<Int>> = ArrayList() // alternatively: = mutableListOf()

seqList.add(mutableListOf<Int>(1, 2, 3))

Also note the mutableListOf and arrayListOf methods in the standard library, which are handy for creating lists instead of directly using the constructor of, say, ArrayList.