type List[T] = ref object
  innerSeq:  seq[T]

proc newList[T](): List[T] = List[T](innerSeq: newSeq[T]())

proc add[T](list: List[T], t: T) = add list.innerSeq, t

iterator items[T](list: List[T]): T =
  for i in list.innerSeq:
    yield i

# etc ...

let list = newList[int]()
add list, 5
add list, 6

for i in list:
  echo i