type
  A = ref object of RootObj
  AA = ref object of A
  BB = ref object of A
  CC = ref object of A
  E = ref object of RootObj
    field: A
 
method doSmt(a: A, i: int): iterator() = return iterator() = echo "A" & repr(i)
method doSmt(a: AA, i: int): iterator() = return iterator() = echo "AA" & repr(i)
method doSmt(a: BB, i: int): iterator() = return iterator() = echo "BB" & repr(i)
method doSmt(a: CC, i: int): iterator() = return iterator() = echo "CC" & repr(i)
 
let a: A = AA()
a.doSmt(1)()
 
let e: E = E(field: BB())
e.field.doSmt(2)()

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