From: Peter Ertl <pertl@...>
Date: 2006-03-24T22:27:58+09:00
Subject: Re: iterator class not working

Hello Robert,

thanks for your feedback.

Yield'ing and using Array.[] seems obvious but I want class 'Iterator' to
work for any 'Enumerable', not only 'Array'.

The intention for using 'binding' is that I expect / hope it will keep track
of the enumeration state inside 'Enumeration.each'. However, I don't know if
that's possible in ruby at all.



> --- Urspr�ngliche Nachricht ---
> Von: "Robert Dober" <robert.dober@gmail.com>
> An: ruby-talk@ruby-lang.org (ruby-talk ML)
> Betreff: Re: iterator class not working
> Datum: Fri, 24 Mar 2006 22:17:32 +0900
> 
> On 3/24/06, Peter Ertl <pertl@gmx.org> wrote:
> >
> > Hi,
> >
> > in order to understand ruby better (and for fun reasons of course) I try
> > to
> > write an iterator class. this way I want to understand  'binding' and
> > 'callcc' better.
> >
> > however, it does not work! :-(
> >
> > any help will be greatly appreciated!!!
> >
> > ---------------------------------------------
> >
> > class Iterator
> >
> >   def initialize(enum)
> >     @context = binding
> >   end
> >
> >   def next
> >     enum = eval("enum", @context)
> >     @context, item = callcc do |cont|
> >       enum.each do |item|
> >         cont.call binding, item
> 
> 
>                         ^
>                         |
> ------------------------+
> you are missing "state" here, each time you call next, you start to
> iterate
> over your "enum" and
> jump out of the iterator at the first iteration, that is giving you "mary"
> all the time.
> 
> 
>       end
> >     end
> >     item
> >   end
> >
> > end
> >
> > names = %w{mary gordy john jane elwood}
> >
> > it = Iterator.new(names)
> >
> > 3.times do
> >   puts it.next
> > end
> >
> > > mary
> > > mary
> > > mary
> >
> > Best regards
> > Peter
> >
> >
> Well I see why it does not work, but I fail to see your design behind the
> thing
> it could be done like this
> class Iterator
>     def initialize(*args); @items=args;@i=-1;end
> 
>     def next
> @i+=1; return @items[@i] unless block_given?; yield @items[@i]; end
> end
> but I do not really know what that would be good for.
> 
> Cheers
> Robert
> 
> --
> Deux choses sont infinies : l'univers et la b�tise humaine ; en ce qui
> concerne l'univers, je n'en ai pas acquis la certitude absolue.
> 
> - Albert Einstein
>