From: Brian Candler <B.Candler@...>
Date: 2007-04-03T16:50:50+09:00
Subject: Re: Last iteration condition

On Tue, Apr 03, 2007 at 03:31:09PM +0900, Gary Wright wrote:
> Building off of Brian's suggestion in that thread, here
> is a way to provide a 'countdown' as the end of the iteration
> approaches.  Default is to only flag the last item but you
> can ask for any number of items to be flagged.

Interesting. Maybe it would be cleaner to return nil for all non-countdown
items, and then n-1, n-2 ... 0 as the flag (or n, n-1 ... 1). e.g.

require 'stringio'
module Enumerable
def each_with_countdown(count=1)
   queue = []
   each do |item|
     queue.push(item)
     yield queue.shift, nil if queue.size > count
   end
   queue.each_with_index do |item, index|
     yield item, count - index - 1
   end
end
end

[1,2,3,4,5,6].each_with_countdown(3) { |item, rem|
  case rem
  when nil
    puts "#{item}"
  when 2
    puts "#{item}, next to next to last item!"
  when 1
    puts "#{item}, next to last item!"
  when 0
    puts "#{item}, last item"
  end
}

[1,2,3,4,5,6].each_with_countdown(1) { |item, rem|
  puts "#{item}, rem: #{rem.inspect}"
}

[1].each_with_countdown { |item, rem|
  puts "#{item}, rem: #{rem.inspect}"
}

StringIO.new("line1\nline2\nline3").each_with_countdown do |line, rem|
  if rem
    puts "last: #{line}"
  else
    puts line
  end
end