Class::Data::Inheritable - Inheritable, overridable class data |
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 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. $suitcase = Raygun->Suitcase;
Raygun inherits its Suitcase class data from Pere::Ubu.
Inheritance of class data works analogous to method inheritance. As
long as Raygun does not ``override'' its inherited class data (by using
Suitcase()
to set a new value) it will continue to use whatever is set
in Pere::Ubu and inherit further changes:
# Both Raygun's and Pere::Ubu's suitcases are now Blue Pere::Ubu->Suitcase('Blue');
However, should Raygun decide to set its own Suitcase()
it has now
``overridden'' Pere::Ubu and is on its own, just like if it had
overriden a method:
# Raygun has an orange suitcase, Pere::Ubu's is still Blue. Raygun->Suitcase('Orange');
Now that Raygun has overridden Pere::Ubu futher changes by Pere::Ubu no longer effect Raygun.
# Raygun still has an orange suitcase, but Pere::Ubu is using Samsonite. Pere::Ubu->Suitcase('Samsonite');
Class->mk_classdata($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.
the perltooc manpage has a very elaborate discussion of class data in Perl.
Class::Data::Inheritable - Inheritable, overridable class data |