Class::Data::Inheritable

NAME

Class::Data::Inheritable − Inheritable, overridable class data

SYNOPSIS

package Stuff;
use base qw(Class::Data::Inheritable);
# Set up DataFile as inheritable class data.
Stuff−>mk_classdata('DataFile');
# Declare the location of the data file for this class.
Stuff−>DataFile('/etc/stuff/data');
# Or, all in one shot:
Stuff−>mk_classdata(DataFile => '/etc/stuff/data');

DESCRIPTION

Class::Data::Inheritable is for creating accessor/mutators to class data. That is, if you want to store something about your class as a whole (instead of about a single object). This data is then inherited by your subclasses and can be overriden.

For example:

Pere::Ubu−>mk_classdata('Suitcase');

will generate the method Suitcase() in the class Pere::Ubu.

This new method can be used to get and set a piece of class data.

Pere::Ubu−>Suitcase('Red');
$suitcase = Pere::Ubu−>Suitcase;

The interesting part happens when a class inherits from Pere::Ubu:

package Raygun;
use base qw(Pere::Ubu);
# Raygun's suitcase is Red.
$suitcase = Raygun−>Suitcase;

Raygun inherits its Suitcase class data from Pere::Ubu.

Inheritance of class data works analogous to method inheritance. As long as Raygun does not "override" its inherited class data (by using Suitcase() to set a new value) it will continue to use whatever is set in Pere::Ubu and inherit further changes:

# Both Raygun's and Pere::Ubu's suitcases are now Blue
Pere::Ubu−>Suitcase('Blue');

However, should Raygun decide to set its own Suitcase() it has now "overridden" Pere::Ubu and is on its own, just like if it had overriden a method:

# Raygun has an orange suitcase, Pere::Ubu's is still Blue.
Raygun−>Suitcase('Orange');

Now that Raygun has overridden Pere::Ubu futher changes by Pere::Ubu no longer effect Raygun.

# Raygun still has an orange suitcase, but Pere::Ubu is using Samsonite.
Pere::Ubu−>Suitcase('Samsonite');

Methods

mk_classdata
Class−>mk_classdata($data_accessor_name);
Class−>mk_classdata($data_accessor_name => $value);

This is a class method used to declare new class data accessors. A new accessor will be created in the Class using the name from $data_accessor_name, and optionally initially setting it to the given value.

To facilitate overriding, mk_classdata creates an alias to the accessor, _field_accessor(). So Suitcase() would have an alias _Suitcase_accessor() that does the exact same thing as Suitcase(). This is useful if you want to alter the behavior of a single accessor yet still get the benefits of inheritable class data. For example.

sub Suitcase {
my($self) = shift;
warn "Fashion tragedy" if @_ and $_[0] eq 'Plaid';
$self−>_Suitcase_accessor(@_);
}

AUTHOR

Original code by Damian Conway.

Maintained by Michael G Schwern until September 2005.

Now maintained by Tony Bowden.

BUGS and QUERIES

Please direct all correspondence regarding this module to:
bug−Class−Data−Inheritable@rt.cpan.org

COPYRIGHT and LICENSE

Copyright (c) 2000−2005, Damian Conway and Michael G Schwern. All Rights Reserved.

This module is free software. It may be used, redistributed and/or modified under the same terms as Perl itself.

SEE ALSO

perltooc has a very elaborate discussion of class data in Perl.