| Current File : //proc/thread-self/root/usr/share/perl5/Class/Data/Inheritable.pm |
package Class::Data::Inheritable;
use strict qw(vars subs);
use vars qw($VERSION);
$VERSION = '0.08';
sub mk_classdata {
my ($declaredclass, $attribute, $data) = @_;
if( ref $declaredclass ) {
require Carp;
Carp::croak("mk_classdata() is a class method, not an object method");
}
my $accessor = sub {
my $wantclass = ref($_[0]) || $_[0];
return $wantclass->mk_classdata($attribute)->(@_)
if @_>1 && $wantclass ne $declaredclass;
$data = $_[1] if @_>1;
return $data;
};
my $alias = "_${attribute}_accessor";
*{$declaredclass.'::'.$attribute} = $accessor;
*{$declaredclass.'::'.$alias} = $accessor;
}
1;
__END__
=head1 NAME
Class::Data::Inheritable - Inheritable, overridable class data
=head1 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');
=head1 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.
$suitcase = Raygun->Suitcase;
Raygun inherits its Suitcase class data from Pere::Ubu.
Inheritance of class data works analogous to method inheritance. As
long as Raygun does not "override" its inherited class data (by using
Suitcase() to set a new value) it will continue to use whatever is set
in Pere::Ubu and inherit further changes:
# Both Raygun's and Pere::Ubu's suitcases are now Blue
Pere::Ubu->Suitcase('Blue');
However, should Raygun decide to set its own Suitcase() it has now
"overridden" Pere::Ubu and is on its own, just like if it had
overridden a method:
# Raygun has an orange suitcase, Pere::Ubu's is still Blue.
Raygun->Suitcase('Orange');
Now that Raygun has overridden Pere::Ubu further changes by Pere::Ubu
no longer effect Raygun.
# Raygun still has an orange suitcase, but Pere::Ubu is using Samsonite.
Pere::Ubu->Suitcase('Samsonite');
=head1 Methods
=head2 mk_classdata
Class->mk_classdata($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(@_);
}
=head1 AUTHOR
Original code by Damian Conway.
Maintained by Michael G Schwern until September 2005.
Now maintained by Tony Bowden.
=head1 BUGS and QUERIES
Please direct all correspondence regarding this module to:
bug-Class-Data-Inheritable@rt.cpan.org
=head1 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.
=head1 SEE ALSO
L<perltooc> has a very elaborate discussion of class data in Perl.