[doc] Steer users trying to find $# documentation

[jidanni]

perlvar says

  $#      $# was a variable that could be used to format printed numbers.
          After  a  deprecation  cycle,  its  magic  was  removed in Perl
          v5.10.0 and using it now triggers a warning: "$# is  no  longer
          supported".

          This  is not the sigil you use in front of an array name to get
          the last index, like $#array.  That's still  how  you  get  the
          last  index  of  an  array in Perl **(see perldata?)**. The two have nothing to do
          with each other.

Please add the starred stuff I inserted. I am just guessing what should be added.

[rwp0]

That twigil syntax could indeed be very confusing, I think.

[iabyn]

On Fri, Dec 01, 2023 at 04:01:58PM -0800, Elvin Aslanov wrote:

To be honest I never understood the need for a separate @.***notation when there is$array[-1]`.

What's the difference, if any, and is it really mentioned somewhere?

I'm not sure what you're referring to here.

This ticket concerns the second of these two:

@a = qw(a b c d);
$size = @a;
$last = $#a;
print "size=$size last=$last\n"; # prints "size=4 last=3"

$#a is usually one smaller than @.***) (it might have been different when we allowed perl to start array indexes at other than 0). Other than that, the main difference is that $#a is assignable to, which can be used to efficiently pre-size or shrink an array:

my @a;
$#a = 999; # pre-allocate slots for 1000 elements
push @a, ... for 0..999;

-- O Unicef Clearasil! Gibberish and Drivel! -- "Bored of the Rings"

[rwp0]

On Fri, Dec 01, 2023 at 04:01:58PM -0800, Elvin Aslanov wrote:

To be honest I never understood the need for a separate @.***notation when there is$array[-1]`.

What's the difference, if any, and is it really mentioned somewhere?

I'm not sure what you're referring to here.

This ticket concerns the second of these two:

@a = qw(a b c d);
$size = @a;
$last = $#a;
print "size=$size last=$last\n"; # prints "size=4 last=3"

$#a is usually one smaller than @.***) (it might have been different when we allowed perl to start array indexes at other than 0). Other than that, the main difference is that $#a is assignable to, which can be used to efficiently pre-size or shrink an array:

my @a;
$#a = 999; # pre-allocate slots for 1000 elements
push @a, ... for 0..999;

-- O Unicef Clearasil! Gibberish and Drivel! -- "Bored of the Rings"

Yes I got confused, sorry. Deleted my comment in GitHub, but seems like they remain in emails 😊.