last property
Returns the last element.
Throws a StateError if this is empty.
Otherwise may iterate through the elements and returns the last one
seen.
Some iterables may have more efficient ways to find the last element
(for example a list can directly access the last element,
without iterating through the previous ones).
Implementation
E get last {
if (_head == _tail) throw IterableElementError.noElement();
return _table[(_tail - 1) & (_table.length - 1)];
}