Re: proposed addition to perlvar

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
    $


Abigail