#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 overridden.

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 overridden a method:

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

Now that Raygun has overridden Pere::Ubu further 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

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.

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