I have some class C:

class C (...) { ... }

I want to use it to index an efficient map. The most efficient map is an Array. So I add a "global" "static" counter in companion object to give each object unique id:

object C {
  var id_counter = 0
}

In primary constructor of C, with each creation of C I want to remember global counter value and increase it.
Question 1: How to do it?

Now I can use id in C objects as perfect hash to index array. But array does not preserve type information like map would, that a given array is indexed by C's id.

Question 2: Is it possible to have it with type safety?