type
  PBase = ref object of RootObj
  POne = ref object of PBase
    x: int
  PTwo = ref object of POne
    y: int

iterator elems(o: PBase): int =
    quit "to override!"

iterator elems(o: POne): int =
    yield o.x

iterator elems(o: PTwo): int =
    yield o.x
    yield o.y

proc printElems(o: PBase) =
    for e in elems(o):
        echo "E: ", e

printElems(POne(x: 100))
echo "-----"
printElems(PTwo(x: 1, y: 2))