From: Pit Capitain <pit@...>
Date: 2004-08-11T06:20:30+09:00
Subject: Re: FirstEachLast, an extension to the Enumerable module.

Robert Klemme wrote:
>The index clearly belongs to the *iteration* and not the elements.

Then you should create a new object for the iteration state. How about this:

   module Enumerable

     class State

       include Enumerable

       def initialize enum
         @enum = enum
         @index = -1
       end

       def each
         @enum.each do |e|
           if @last.nil?
             @last = false
           else
             @index += 1
             yield @next
           end
           @next = e
         end
         unless @last.nil?
           @last = true
           @index += 1
           yield @next
         end
       end

       def first?
         @index == 0
       end

       def index
         @index
       end

       def last?
         @last
       end

     end

     def state
       State.new self
     end

   end


Now you can get an EnumState object from a normal enumerable and iterate over 
the EnumState object:

   state = %w"does it work?".state

   state.each do |e|
     puts "%-5s %-5s %i %s" % [ e, state.first?, state.index, state.last? ]
   end

=>

   does  true  0 false
   it    false 1 false
   work? false 2 true


Regards,
Pit