Tie::RefHash::Weak(3pm) 				User Contributed Perl Documentation				   Tie::RefHash::Weak(3pm)

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

perl v5.10.1							    2008-10-18						   Tie::RefHash::Weak(3pm)