From: dblack@...
Date: 2003-08-30T04:14:47+09:00
Subject: Re: #collect with block modifying receiver

Hi --

On Sat, 30 Aug 2003, Hal Fulton wrote:

> dblack@superlink.net wrote:
> >>>I wouldn't like that, personally. I don't remember exactly where, but I
> >>>believe that I have a piece of code taking advantage of the fact that a
> >>>receiver *can* be modified during iteration. I don't modify during a
> >>>#collect, but during an #each. One of the things you can do is:
> >>>
> >>>  arr.each { |e| arr << f.flatten if f.kind_of?(Array) }
> >>
> >>Well, if I understand Matz correctly, this behavior is not guaranteed.
> >>
> >>If that's the case, you should change this to avoid being bitten
> >>the way I was.
> >
> >
> > I think (Matz - ?) that Matz was talking specifically about changing
> > the length of the receiver during an iteration, since that raises the
> > question of how many iterations there should be, what the next one
> > should be if something gets sliced out, etc.
> >
> > Just modifying the objects during an iteration is different, I think.
> > #map! does it, for example.  Or:
> >
> >   names.each {|name| name.upcase!}
> >
> > I'm pretty sure there's no danger with in-place things like this
> > (as opposed to things that alter the meaning of the 'place' you're
> > 'in' :-)
>
> Yes, I agree. But to avoid confusion for others, let me point out that
> Austin's code *does* change the length of the receiver.

Whoops -- too late to prevent confusion for me.  My only excuse is
that I was so focused on wondering what 'f' was that I lost track of
what was actually happening :-)


David

-- 
David Alan Black
home: dblack@superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav