That doesn't explain why $#a is behaving so oddly when I retrieve its value.

When you set $#a, Perl needs an integer. If you give it something that's more than just an integer, it takes out the integer part and stores that in the appropriate place in the data structure it uses to represent the array. It throws out the rest of the information, as it doesn't need it.

When you read $#a, Perl looks in the underlying data structure and fetches the integer stored there. It returns it. It can't return any more information. It doesn't store it.

This is C-level stuff. If you're curious, see av.h, specifically the xpvav struct declaration and the xav_fill member. It holds an integer (see uconfig.h, I think), not an SV.

Update: I did misread the question. The right code to read is that of the av2arylen opcode in pp.c, which I really don't follow. Consider this program though, which shows that $#a isn't a plain integer, it's an SV with magic:

use Devel::Peek;
my @a;
Dump( $#a );

my $b = {foo=>1};
exit if $b + 0 > 0x10125000;

$#a=$b;

Dump( $#a );

[download]

In reply to Re^3: Putting weird things into $#array by chromatic
in thread Putting weird things into $#array by blokhead

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.