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