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