# phpman > info > Tie::RefHash

Tie::[RefHash(3perl)](https://www.chedong.com/phpMan.php/man/RefHash/3perl/markdown)    Perl Programmers Reference Guide    Tie::[RefHash(3perl)](https://www.chedong.com/phpMan.php/man/RefHash/3perl/markdown)

NAME
       [Tie::RefHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash/markdown) - Use references as hash keys

VERSION
       version 1.40

SYNOPSIS
           require 5.004;
           use [Tie::RefHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash/markdown);
           tie HASHVARIABLE, '[Tie::RefHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash/markdown)', LIST;
           tie HASHVARIABLE, '[Tie::RefHash::Nestable](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash%3A%3ANestable/markdown)', LIST;

           untie HASHVARIABLE;

DESCRIPTION
       This module provides the ability to use references as hash keys if you
       first "tie" the hash variable to this module.  Normally, only the keys
       of the tied hash itself are preserved as references; to use references
       as keys in hashes-of-hashes, use [Tie::RefHash::Nestable](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash%3A%3ANestable/markdown), included as
       part of [Tie::RefHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash/markdown).

       It is implemented using the standard perl TIEHASH interface.  Please
       see the "tie" entry in [perlfunc(1)](https://www.chedong.com/phpMan.php/man/perlfunc/1/markdown) and [perltie(1)](https://www.chedong.com/phpMan.php/man/perltie/1/markdown) for more information.

       The Nestable version works by looking for hash references being stored
       and converting them to tied hashes so that they too can have references
       as keys.  This will happen without warning whenever you store a
       reference to one of your own hashes in the tied hash.

EXAMPLE
           use [Tie::RefHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash/markdown);
           tie %h, '[Tie::RefHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash/markdown)';
           $a = [];
           $b = {};
           $c = \*main;
           $d = \"gunk";
           $e = sub { 'foo' };
           %h = ($a => 1, $b => 2, $c => 3, $d => 4, $e => 5);
           $a->[0] = 'foo';
           $b->{foo} = 'bar';
           for (keys %h) {
              print ref($_), "\n";
           }

           tie %h, '[Tie::RefHash::Nestable](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash%3A%3ANestable/markdown)';
           $h{$a}->{$b} = 1;
           for (keys %h, keys %{$h{$a}}) {
              print ref($_), "\n";
           }

THREAD SUPPORT
       [Tie::RefHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash/markdown) fully supports threading using the "CLONE" method.

STORABLE SUPPORT
       Storable hooks are provided for semantically correct serialization and
       cloning of tied refhashes.

SEE ALSO
       [perl(1)](https://www.chedong.com/phpMan.php/man/perl/1/markdown), [perlfunc(1)](https://www.chedong.com/phpMan.php/man/perlfunc/1/markdown), [perltie(1)](https://www.chedong.com/phpMan.php/man/perltie/1/markdown)

SUPPORT
       Bugs may be submitted through the RT bug tracker
       <<https://rt.cpan.org/Public/Dist/Display.html?Name=Tie-RefHash>> (or
       <bug-Tie-RefHash@rt.cpan.org> <mailto:<bug-Tie-RefHash@rt.cpan.org>>).

AUTHORS
       Gurusamy Sarathy <<gsar@activestate.com>>

       [Tie::RefHash::Nestable](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3ARefHash%3A%3ANestable/markdown) by Ed Avis <<ed@membled.com>>

CONTRIBUTORS
       o   Yuval Kogman <<nothingmuch@woobling.org>>

       o   Karen Etheridge <<ether@cpan.org>>

       o   Florian Ragwitz <<rafl@debian.org>>

       o   Jerry D. Hedden <<jdhedden@cpan.org>>

COPYRIGHT AND LICENCE
       This software is copyright (c) 2006 by  ' (Yuval Kogman)
       <<nothingmuch@woobling.org>>.

       This is free software; you can redistribute it and/or modify it under
       the same terms as the Perl 5 programming language system itself.

perl v5.34.0                      2025-07-25               Tie::[RefHash(3perl)](https://www.chedong.com/phpMan.php/man/RefHash/3perl/markdown)