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−[email protected]
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.