js.compile.ignore=true
=====
>>> main.whiley
public export method test():
   int[][] xs = [[1],[2],[3]]
   int[][] ys = xs[1:=[4]]
   // check xs unchanged
   assert xs[0] == [1] 
   assert xs[1] == [2]
   assert xs[2] == [3]
   // check ys changed
   assert ys[0] == [1] 
   assert ys[1] == [4]
   assert ys[2] == [3]
   // Final check
   assert ys == [[1],[4],[3]]
---