Oh, that's quite on the mark!

Nitpicking: I'm not fond of reserving keywords like len or append.

  len(arr)
  append(arr, v)

Better is

  arr.len
  arr.append(v)

Also

  x: [dynamic]int

is quite verbose

Maybe better would be

  x: [int]   //dyn
  x: [int,2] //fixed