Tie::RefHash

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;