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+package Tie::RefHash;
+
+our $VERSION = 1.32;
+
+=head1 NAME
+
+Tie::RefHash - use references as hash keys
+
+=head1 SYNOPSIS
+
+ require 5.004;
+ use Tie::RefHash;
+ tie HASHVARIABLE, 'Tie::RefHash', LIST;
+ tie HASHVARIABLE, 'Tie::RefHash::Nestable', LIST;
+
+ untie HASHVARIABLE;
+
+=head1 DESCRIPTION
+
+This module provides the ability to use references as hash keys if you
+first C<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,
+included as part of Tie::RefHash.
+
+It is implemented using the standard perl TIEHASH interface. Please
+see the C<tie> entry in perlfunc(1) and perltie(1) 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.
+
+=head1 EXAMPLE
+
+ use Tie::RefHash;
+ tie %h, 'Tie::RefHash';
+ $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';
+ $h{$a}->{$b} = 1;
+ for (keys %h, keys %{$h{$a}}) {
+ print ref($_), "\n";
+ }
+
+=head1 AUTHOR
+
+Gurusamy Sarathy gsar@activestate.com
+
+'Nestable' by Ed Avis ed@membled.com
+
+=head1 VERSION
+
+Version 1.32
+
+=head1 SEE ALSO
+
+perl(1), perlfunc(1), perltie(1)
+
+=cut
+
+use Tie::Hash;
+use vars '@ISA';
+@ISA = qw(Tie::Hash);
+use strict;
+
+require overload; # to support objects with overloaded ""
+
+sub TIEHASH {
+ my $c = shift;
+ my $s = [];
+ bless $s, $c;
+ while (@_) {
+ $s->STORE(shift, shift);
+ }
+ return $s;
+}
+
+sub FETCH {
+ my($s, $k) = @_;
+ if (ref $k) {
+ my $kstr = overload::StrVal($k);
+ if (defined $s->[0]{$kstr}) {
+ $s->[0]{$kstr}[1];
+ }
+ else {
+ undef;
+ }
+ }
+ else {
+ $s->[1]{$k};
+ }
+}
+
+sub STORE {
+ my($s, $k, $v) = @_;
+ if (ref $k) {
+ $s->[0]{overload::StrVal($k)} = [$k, $v];
+ }
+ else {
+ $s->[1]{$k} = $v;
+ }
+ $v;
+}
+
+sub DELETE {
+ my($s, $k) = @_;
+ (ref $k)
+ ? (delete($s->[0]{overload::StrVal($k)}) || [])->[1]
+ : delete($s->[1]{$k});
+}
+
+sub EXISTS {
+ my($s, $k) = @_;
+ (ref $k) ? exists($s->[0]{overload::StrVal($k)}) : exists($s->[1]{$k});
+}
+
+sub FIRSTKEY {
+ my $s = shift;
+ keys %{$s->[0]}; # reset iterator
+ keys %{$s->[1]}; # reset iterator
+ $s->[2] = 0; # flag for iteration, see NEXTKEY
+ $s->NEXTKEY;
+}
+
+sub NEXTKEY {
+ my $s = shift;
+ my ($k, $v);
+ if (!$s->[2]) {
+ if (($k, $v) = each %{$s->[0]}) {
+ return $v->[0];
+ }
+ else {
+ $s->[2] = 1;
+ }
+ }
+ return each %{$s->[1]};
+}
+
+sub CLEAR {
+ my $s = shift;
+ $s->[2] = 0;
+ %{$s->[0]} = ();
+ %{$s->[1]} = ();
+}
+
+package Tie::RefHash::Nestable;
+use vars '@ISA';
+@ISA = 'Tie::RefHash';
+
+sub STORE {
+ my($s, $k, $v) = @_;
+ if (ref($v) eq 'HASH' and not tied %$v) {
+ my @elems = %$v;
+ tie %$v, ref($s), @elems;
+ }
+ $s->SUPER::STORE($k, $v);
+}
+
+1;