NAME

       Tie::RefHash::Weak - A Tie::RefHash subclass with weakened references in the keys.

SYNOPSIS

               use Tie::RefHash::Weak;
               tie my %h, 'Tie::RefHash::Weak';

               # OR:

               use Tie::RefHash::Weak 'fieldhash';
               fieldhash my %h;

               { # new scope
                       my $val = "foo";

                       $h{\$val} = "bar"; # key is weak ref

                       print join(", ", keys %h); # contains \$val, returns regular reference
               }
               # $val goes out of scope, refcount goes to zero
               # weak references to \$val are now undefined

               keys %h; # no longer contains \$val

               # see also Tie::RefHash

DESCRIPTION

       The Tie::RefHash module can be used to access hashes by reference. This is useful when you
       index by object, for example.

       The problem with Tie::RefHash, and cross indexing, is that sometimes the index should not
       contain strong references to the objecs. Tie::RefHash's internal structures contain strong
       references to the key, and provide no convenient means to make those references weak.

       This subclass of Tie::RefHash has weak keys, instead of strong ones. The values are left
       unaltered, and you'll have to make sure there are no strong references there yourself.

FUNCTIONS

       For compatibility with Hash::Util::FieldHash, this module will, upon request, export the
       following two functions. You may also write "use Tie::RefHash::Weak ':all'".

       fieldhash %hash
           This ties the hash and returns a reference to it.

       fieldhashes \%hash1, \%hash2 ...
           This ties each hash that is passed to it as a reference. It returns the list of
           references in list context, or the number of hashes in scalar context.

THREAD SAFETY

       Tie::RefHash version 1.32 and above have correct handling of threads (with respect to
       changing reference addresses). If your module requires Tie::RefHash::Weak to be thread
       aware you need to depend on both Tie::RefHash::Weak and Tie::RefHash version 1.32 (or
       later).

       Version 0.02 and later of Tie::RefHash::Weak depend on a thread-safe version of
       Tie::RefHash anyway, so if you are using the latest version this should already be taken
       care of for you.

5.10.0 COMPATIBILITY

       Due to a minor change in Perl 5.10.0 a bug in the handling of magic freeing was uncovered
       causing segmentation faults.

       This has been patched but not released yet, as of 0.08.

CAVEAT

       You can use an LVALUE reference (such as "\substr ...") as a hash key, but due to a bug in
       perl (see <http://rt.perl.org/rt3/Public/Bug/Display.html?id=46943>) it might not be
       possible to weaken a reference to it, in which case the hash element will never be deleted
       automatically.

AUTHORS

       Yuval Kogman <nothingmuch@woobling.org>

       some maintenance by Hans Dieter Pearcey <hdp@pobox.com>

COPYRIGHT & LICENSE

               Copyright (c) 2004 Yuval Kogman. All rights reserved
               This program is free software; you can redistribute
               it and/or modify it under the same terms as Perl itself.

SEE ALSO

       Tie::RefHash, Class::DBI (the live object cache), "Perl_magic_killbackrefs" in mg.c