From: Robert Dober <robert.dober@...>
Date: 2009-06-12T21:46:07+09:00
Subject: Re: Idiomatic way to detect first/last iteration?

On Thu, Jun 11, 2009 at 6:43 PM, Kendall Gifford<zettabyte@gmail.com> wrote:
> Hi there, is there any recognized ruby idiomatic way for detecting
> when you're on the first and/or last iteration over a collection? Or,
> if not, anyone know of any tricky ways?
>
> Specifically, I'm trying to avoid using each_with_index (as shown
> below):
>
> genres = %w{ classical punk rock jazz }
> genres.each_with_index do |genre, i|
>  desc = "one of my favorites"
>  desc = "my absolute favorite" if i.zero?
>  desc = "my least fav. of all my favorites" if i + 1 == genres.length
>  puts "#{genre} is #{desc}"
> end
>
> I just don't like having to compare an index value (especially as when
> detecting the final iteration) and hate even having it as a loop
> parameter unless absolutely necessary. I know, I'm picky. Just wanted
> to beat the bushes and see if any cool alternatives pop up.
>
>
Kendall

streams might give you the abstraction you need

--------------- 8< ------------------------
require 'lab419/functional/streams/core'
require 'lab419/functional/streams/as-enums'

x = %w{a b c a b}.to_stream

x.each do | s |
  p [ s.head, s.tail == EmptyStream ]
end
----------------- >8 ----------------

I might implement SimpleStream#first?, SimpleStream#last? and
SimpleStream#middle? if I find some spare time, and if anybody needs
it ;)

I admit however that there is still a little price to pay, you might
have noticed that s is a stream and not an element of the stream, but
that is just the way streams work.

HTH
Robert



-- 
Toutes les grandes personnes ont d’abord été des enfants, mais peu
d’entre elles s’en souviennent.

All adults have been children first, but not many remember.

[Antoine de Saint-Exupéry]