Challenge 2: Manual Stepping With an Enumerator — Solution

letters = ["a", "b", "c", "d"]
enum = letters.each

puts enum.next
puts enum.next
puts enum.next
puts enum.peek

=begin
Output:
a
b
c
d

Notes:
- letters.each is called with no block, so instead of iterating
  immediately, it returns an Enumerator object bound to letters,
  paused before its first element.
- Each call to enum.next pulls exactly one value and advances the
  Enumerator's internal position by one — three calls yield "a", "b",
  then "c" in that order.
- enum.peek looks at the next value ("d") without advancing the
  Enumerator, which is why a fourth enum.next call afterward (not shown
  here) would still return "d" rather than raising StopIteration.
=end