By "not documented', I was refering to what is supposed to be returned by sort.
To a Perl programer, should what's returned by sort be considered a 'true' copy
of a original list (albeit sorted) which can be worked on without affecting the
original list under any circumstances? As far as I see it, in the code
of 'foreach (sort @array){}', foreach is stepping through a sorted copy
returned by sort at the time sort has already finished and @array forgotten.
So I wouldn't expect @array to be changed. The current behavior is a bad
behavior to say the least. I would be very surprised if Larry would design
the code to behave in such a way. ;-)
> From [EMAIL PROTECTED] Fri Jul 22 09:07:30 2005
> Subject: Re: [perl #36616] bug or feature? foreach (sort @array)
> {y/a-z/A-Z/;} # @array modified!
> From: "Scott R. Godin via RT" <[EMAIL PROTECTED]>
> X-RT-Loop-Prevention: perl
> RT-Ticket: perl #36616
> Managed-by: RT 3.0.11 (http://www.bestpractical.com/rt/)
> RT-Originator: [EMAIL PROTECTED]
> To: [EMAIL PROTECTED]
> X-RT-Original-Encoding: utf-8
> Date: Fri, 22 Jul 2005 06:05:23 -0700
> MIME-Version: 1.0
> Content-Transfer-Encoding: 7bit
>
> Shiping Zhang wrote:
>
> >>The described behavior changes whether "sort @arr" goes directly in
> >>'for' or you assign it first to an array variable.
> >>
> >> @arr = ('one', 'two', 'three', 'four');
> >> y/a-z/A-Z/ foreach sort @arr;
> >> print "\na: @arr\n"
> >>
> >>prints "a: ONE TWO THREE FOUR" and
> >>
> >> @arr = ('one', 'two', 'three', 'four');
> >> @s = sort @arr;
> >> y/a-z/A-Z/ foreach @s;
> >> print "\na: @arr\n"
> >>
> >>prints "a: one two three four". This has to do with copy-on-assign?
> >>
> >>That seems like a (subtle) feature. Otherwise, it is a very old bug:
> >>the same behavior with 5.8.6, 5.6.1, and 5.005_03.
> >>
>
> > If it's a feature, then it's not documented at all. Larry's Perl books do
> > not
> > mention it, the sort man page from perldoc does not mention it, and the
> > manual
> > page from www.perl.org does not mention it. And this feature is against
> > intuition and I would consider it more a bug than a feature (what use it
> > has?).
> > I think other people wouldn't expect @array to be changed in the code above.
> > (New Perl programers may be surprised to know that foreach works on an
> > alias,
> > but it's well documented (and warned) and such feature is at least useful
> > under
> > some circumstances.) Conceptually, sort should return a true copy (sorted
> > of
> > course) of its arguement and I think it is how people would understand it.
> > (How sort is implemented is a different matter. I guess sort is working on a
> > list of pointers to the elements of the original list and, in foreach
> > context,
> > just returns a pointer to the list of pointers instead of making an
> > anonymous
> > copy of the sort list.)
> >
>
> it's documented under perldoc perltrap as a discontinuance between perl4
> and perl5 so it's been around for quite a while.
>
> it's also documented under perldoc perlsyn:
>
> "If any element of LIST is an lvalue, you can modify it by modifying VAR
> inside the loop. Conversely, if any element of LIST is NOT an lvalue,
> any attempt to modify that element will fail. In other words, the
> "foreach" loop index variable is an implicit alias for each item in the
> list that you're looping over."
>
> it's ALSO mentioned in perlfaq4: perldoc -q "strip blank space"
>
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