Class::Data::Inheritable - Inheritable, overridable class data
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');
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.
$suitcase = Raygun->Suitcase;
Raygun inherits its Suitcase class data from Pere::Ubu.
Inheritance of class data works analogous to method inheritance. As
long as Raygun does not ``override'' its inherited class data (by using
Suitcase() to set a new value) it will continue to use whatever is set
in Pere::Ubu and inherit further changes:
# Both Raygun's and Pere::Ubu's suitcases are now Blue
Pere::Ubu->Suitcase('Blue');
However, should Raygun decide to set its own Suitcase() it has now
``overridden'' Pere::Ubu and is on its own, just like if it had
overridden a method:
# Raygun has an orange suitcase, Pere::Ubu's is still Blue.
Raygun->Suitcase('Orange');
Now that Raygun has overridden Pere::Ubu further changes by Pere::Ubu
no longer effect Raygun.
# Raygun still has an orange suitcase, but Pere::Ubu is using Samsonite.
Pere::Ubu->Suitcase('Samsonite');
Class->mk_classdata($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(@_);
}
Original code by Damian Conway.
Maintained by Michael G Schwern until September 2005.
Now maintained by Tony Bowden.
Please direct all correspondence regarding this module to:
bug-Class-Data-Inheritable@rt.cpan.org
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.
perltooc has a very elaborate discussion of class data in Perl.
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