+ # The 17 and 2/3 magic numbers were determined empirically.
+ # Note: the standard hash functions djb2, sbdm and fnv1 were also
+ # tested but were comparable (or worse).
+ var res = 17 + length
+ for e in self do
+ res = res * 3 / 2
+ if e != null then res += e.hash
+ end
+ return res
+ end
+
+ redef fun iterator: IndexedIterator[E] is abstract
+
+ # Gets a new Iterator starting at position `pos`
+ #
+ # var iter = [10,20,30,40,50].iterator_from(2)
+ # assert iter.to_a == [30, 40, 50]
+ fun iterator_from(pos: Int): IndexedIterator[E]
+ do
+ var res = iterator
+ while pos > 0 and res.is_ok do
+ res.next
+ pos -= 1
+ end
+ return res
+ end
+
+ # Gets an iterator starting at the end and going backwards
+ #
+ # var reviter = [1,2,3].reverse_iterator
+ # assert reviter.to_a == [3,2,1]
+ fun reverse_iterator: IndexedIterator[E] is abstract
+
+ # Gets an iterator on the chars of self starting from `pos`
+ #
+ # var reviter = [10,20,30,40,50].reverse_iterator_from(2)
+ # assert reviter.to_a == [30,20,10]
+ fun reverse_iterator_from(pos: Int): IndexedIterator[E]
+ do
+ var res = reverse_iterator
+ while pos > 0 and res.is_ok do
+ res.next
+ pos -= 1
+ end