On Thu, July 21, 2005 3:34 pm, Dave Mitchell said:
> On Thu, Jul 21, 2005 at 01:15:39PM -0700, Michael G Schwern wrote:
>> On Thu, Jul 21, 2005 at 10:20:22AM -0400, Shiping Zhang wrote:
>> > But shouldn't the alias be to the elements of the list returned by
>> sort,
>> > not to the elements of the original list? Should sort sort a copy of
>> its
>> > argument and return the sorted copy?
>>
>> That's what I'm thinking, that this is a sort/foreach optimization gone
>> wrong. foreach $_ works on aliases of the array its looping over but
>> sort
>> does NOT sort in place. "foreach (sort @a)" should not loop over
>> aliases
>> to @a any more than "foreach (map {$_} @a)" should.
>
> I wouldn't expect map to maintain the alias, because map returns the
> result of an expression; on the other hand, grep, like sort, returns the
> original values, and like sort, it maintains the alias:
>
> $ perl587 -we '@a=qw(1 2 3); for (grep /\d/, @a) { $_++ } print
> "@a\n"'
> 2 3 4
> $
>
> I don't think its a bug so much as undocumented behaviour. "fixing" it
> would involve doing a whole bunch of unneccessary copying in sort and
> grep.
And reverse and any XS sub that directly returns any of its
SV arguments (eg List::Util::shuffle), not to mention any sub
that returns a slice of @_
Graham.
