Enumerable
self[nth]
Return nth item. If index is negative,
counts from the end. The index of last item is -1.
Return nil
if nth item is not exists.
self[start..end]
Returns an array containing the objects from start to end.
self[start, length]
Returns an array containing length items from start.
self[nth] = val
Set nth item into val.
each {|item|...}
Iterate over each item.
include?(val)
Return true if sequence contains val.
length
size
Return number of items.