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 CW$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-Bit-Vector-Minimal@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 terms of the Perl Artistic License (see http://www.perl.com/perl/misc/Artistic.html)

perltootc has a very elaborate discussion of class data in Perl.