Once the reference is assigned a location, it never moves. The data behind it may get moved, but the reference you see doesn't.

There are only four major gotchas to using references as hash keys that I know of.

  1. It depends on stringification, so if the generator of the reference likes overloading, all bets are off.
  2. From the string representation of a reference you can't get the reference back.
  3. Names are guaranteed unique at any point in time, but not over time. As demonstrated in my code sample, it is possible for 2 references to get the same name if the second is created after the first is destroyed.
  4. If you ever make your program persistent by freezing and thawing data structures (eg with Storable or Data::Dumper) then the reconstructed references will be at new addresses.
And yes, this fact does have some neat uses.

In reply to Re (tilly) 3: What is HASH(0x17653d4) for? by tilly
in thread What is HASH(0x17653d4) for? by Tetramin

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.