1Tie::RefHash::Weak(3) User Contributed Perl DocumentationTie::RefHash::Weak(3)
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NAME

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

10               use Tie::RefHash::Weak;
11               tie my %h, 'Tie::RefHash::Weak';
12
13               # OR:
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15               use Tie::RefHash::Weak 'fieldhash';
16               fieldhash my %h;
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18               { # new scope
19                       my $val = "foo";
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21                       $h{\$val} = "bar"; # key is weak ref
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23                       print join(", ", keys %h); # contains \$val, returns regular reference
24               }
25               # $val goes out of scope, refcount goes to zero
26               # weak references to \$val are now undefined
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28               keys %h; # no longer contains \$val
29
30               # see also Tie::RefHash
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DESCRIPTION

33       The Tie::RefHash module can be used to access hashes by reference. This
34       is useful when you index by object, for example.
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36       The problem with Tie::RefHash, and cross indexing, is that sometimes
37       the index should not contain strong references to the objecs.
38       Tie::RefHash's internal structures contain strong references to the
39       key, and provide no convenient means to make those references weak.
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41       This subclass of Tie::RefHash has weak keys, instead of strong ones.
42       The values are left unaltered, and you'll have to make sure there are
43       no strong references there yourself.
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FUNCTIONS

46       For compatibility with Hash::Util::FieldHash, this module will, upon
47       request, export the following two functions. You may also write "use
48       Tie::RefHash::Weak ':all'".
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50       fieldhash %hash
51           This ties the hash and returns a reference to it.
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53       fieldhashes \%hash1, \%hash2 ...
54           This ties each hash that is passed to it as a reference. It returns
55           the list of references in list context, or the number of hashes in
56           scalar context.
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THREAD SAFETY

59       Tie::RefHash version 1.32 and above have correct handling of threads
60       (with respect to changing reference addresses). If your module requires
61       Tie::RefHash::Weak to be thread aware you need to depend on both
62       Tie::RefHash::Weak and Tie::RefHash version 1.32 (or later).
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64       Version 0.02 and later of Tie::RefHash::Weak depend on a thread-safe
65       version of Tie::RefHash anyway, so if you are using the latest version
66       this should already be taken care of for you.
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5.10.0 COMPATIBILITY

69       Due to a minor change in Perl 5.10.0 a bug in the handling of magic
70       freeing was uncovered causing segmentation faults.
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72       This has been patched but not released yet, as of 0.08.
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CAVEAT

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

82       Yuval Kogman <nothingmuch@woobling.org>
83
84       some maintenance by Hans Dieter Pearcey <hdp@pobox.com>
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87               Copyright (c) 2004 Yuval Kogman. All rights reserved
88               This program is free software; you can redistribute
89               it and/or modify it under the same terms as Perl itself.
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SEE ALSO

92       Tie::RefHash, Class::DBI (the live object cache),
93       "Perl_magic_killbackrefs" in mg.c
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97perl v5.34.0                      2022-01-21             Tie::RefHash::Weak(3)
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