Re: proposed addition to perlvar

On 14 June 2010 10:46, Abigail <[email protected]> wrote:
> On Mon, Jun 14, 2010 at 10:04:09AM +0200, demerphq wrote:
>> On 9 June 2010 23:08, Abigail <[email protected]> wrote:
>> > On Wed, Jun 09, 2010 at 02:52:29PM +0000, Matt Sergeant wrote:
>> >> On Tue, 8 Jun 2010, Chas. Owens wrote:
>> >>
>> >>> How about:
>> >>>
>> >>> =item $#
>> >>>
>> >>> C<$#> used to be a variable that could be used to format printed number.
>> >>> After a deprecation cycle, its magic was removed in 5.10 and using it
>> >>> now triggers a severe warning: C<$# is no longer supported>.
>> >>>
>> >>> C<$#> is also used as sigil, which, when prepended on the name of an
>> >>> array gives the index of the last element in that array.
>> >>>
>> >>>    my @a            = ("a", "b", "c");
>> >>>    my $last_index   = $#a;     # $last_index is 2
>> >>>    my $last_element = $a[$#a]; # $last_element is "c"
>> >>
>> >> Do we want to "encourage" this kind of use or prefer to encourage the
>> >> [-1] format?
>> >
>> >
>> > Just because a construct is documented does not imply it's encouraged.
>> > It's important for documentation to be complete. In a section showing
>> > an example of '$#', the example should preferable have as few other
>> > things as possible - I would prefer the above over any foreach construct.
>> > These lines are about $#. Not foreach. Not ranges. And it is code that
>> > people will encounter - and consult the documentation for.
>> >
>> > Let's stay clear of a -1 vs. $#a preference debate. This part of the
>> > documentation is not the place.
>>
>> I agree, but I think it would be the place to note that using $#arry
>> unguarded by an array size assertion may result in a fatal exception.
>
> Fatal exception? Could you provide an example of that?
>
>    $ perl -wE 'my @x; say $x [$#x]; END {say "Hello"}'
>    Use of uninitialized value in say at -e line 1.
>
>    Hello
>    $

My mail was pre-coffee, and i have to admit i thought that fetching -1
on an empty array was an error. You have a collection of old perls
right? Was there an older version where fetching -1 on an empty array
/was/ an error?

Anyway, I meant this exception, for /setting/ the last element in an array:

perl -lwe'use strict; my @array; $array[$#array]=1'
Modification of non-creatable array value attempted, subscript -1 at -e line 1.

Yves


-- 
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