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      $self->SUPER::prepare_comparable(@_);
      delete $self->{some_temp_value};
      $self->items;    # autovivify;
  }

  # in some test file:

  use Test::Differences;
  my $x = '...';
  my $y = '...';
  eq_or_diff($x->comparable, $y->comparable, 'objects are equal');

=head1 DESCRIPTION

When you define a class, it may not be so straightforward to compare two
objects of that class. For example, you want to compare object C<$x> to object
C<$y>. You would like to use C<is_deeply()> from Test::More, but it complains
that some hash keys are undef in one object but completely missing in the
other. That is easily solved by autovivifying the keys in question. Also, some
hash keys might be irrelevant to comparison - that is, you still consider two
objects to be equal even though they differ in some hash keys.

This is where Data::Comparable can help. It enables you to define how your
object wants to look like when it is being passed to some deep comparison
function like C<Test::More::is_deeply()> or
C<Test::Differences::eq_or_diff()>. If your class inherits from
Data::Comparable, it gets a method called C<comparable()>, which you can call
when comparing it. That is, you don't compare the actual objects, but their
comparable versions.

To define the comparable version of your object, your class has to implement
the C<prepare_comparable()> method. There you can autovivify any hash keys you
like or tweak your object in any way you need to make it comparable.

=head1 METHODS

=head2 comparable

FIXME

=head2 comparable_scalar

FIXME

=head2 dump_comparable

FIXME

=head2 prepare_comparable

FIXME

=head2 yaml_dump_comparable

FIXME

=head1 INSTALLATION

See perlmodinstall for information and options on installing Perl modules.

=head1 BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests through the web interface at
L<http://rt.cpan.org/Public/Dist/Display.html?Name=Data-Comparable>.

=head1 AVAILABILITY

The latest version of this module is available from the Comprehensive Perl
Archive Network (CPAN). Visit L<http://www.perl.com/CPAN/> to find a CPAN
site near you, or see
L<http://search.cpan.org/dist/Data-Comparable/>.

The development version lives at
L<http://github.com/hanekomu/Data-Comparable/>.
Instead of sending patches, please fork this project using the standard git
and github infrastructure.

=head1 AUTHOR

  Marcel Gruenauer <marcel@cpan.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2004 by Marcel Gruenauer.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut