NilEnumerator: an enumerator that returns nil instead of a StopIteration exception when it is at the end of the collection

nil_enumerator.rb

# https://gist.github.com/gists/2897543
# NilEnumerator
# 
# an enumerator that yields nil when it is finished.  Only implements #next and
# #peak.  Would only want to use this if your collection does NOT already include
# nils.
# 
# Compare:
#
#     # normal iteration requires catching StopIteration
#     enum = [1,2,3].each
#     begin
#       while item=each.next
#         p item
#       end
#     rescue StopIteration
#     end
# 
#     # nil enumerator just yields nil if it is done
#     enum = [1,2,3].each.nil_enum     # or .to_nil_enum
#     while item=enum.next
#       p item
#     end
#
class NilEnumerator < Enumerator
  def initialize(enum)
    @enum = enum
  end

  def next
    begin
      @enum.next
    rescue StopIteration
      nil
    end
  end

  def peek
    begin
      @enum.peek
    rescue StopIteration
      nil
    end
  end
end

class Enumerator
  def to_nil_enum
    NilEnumerator.new(self)
  end
  alias_method :nil_enum, :to_nil_enum
end