Return
a read-only IntList with nothing in it.
Return
a new read-only IntList with element1 as the only item in the list.
Return
a new read-only IntList with 2 elements, element1 and element2, in order.
Return
a new read-only IntList with 3 elements, element1, element2, and element3, in order.
Return
a new read-only IntList with elements in order.