From: Robert Klemme <bob.news@...>
Date: 2004-08-11T20:51:16+09:00
Subject: Re: empty? and size in Enumerable


"Kristof Bastiaensen" <kristof@vleeuwen.org> schrieb im Newsbeitrag
news:pan.2004.08.11.11.25.43.340597@vleeuwen.org...

> > I've changed my mind here: the contract of Enumerable (or of #each if
you
> > like) is too weak to guarantee a proper implementation of size and
empty?.
> > The requirements on #each are really very weak and you can't provide a
> > proper size and empty? method for each classes using Enumerable.  So
IMHO
> > it's best to leave them out or put them in a separate module.
> >
> > Kind regards
> >
> >     robert
>
> You are right.

Well, in fact *Matz* was right.  I'm just a stupid guy that needed quite a
detour to reach this understanding of the matter.  Thank you for helping
my on this!  Once again learnes something new.

>  While thinking of the best example to support
> my argument, I actually came up with an (non esoteric) example
> that shows your point.
> IO includes enumerable, and reading from an IO will change the IO.

Yeah, there are Enumerables that can yield their sequence only once.

> For example:
>
> require 'stringio'
> io = StringIO.new <<EOS
> first line
> second line
> third line
> EOS
>
> io.map unless io.empty
> => ["second line\n", "third line\n"]

Nice short example that has it all.

> So I think that's really the reason why size and empty? is
> not included.

So finally we reach consensus. :-)

Thanks again!

    robert