Class::Data::Inheritable.3pm

Langue: en

Version: 2008-01-25 (fedora - 01/12/10)

Section: 3 (Bibliothèques de fonctions)

NAME

Class::Data::Inheritable - Inheritable, overridable class data

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');
 
 

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 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');
 
 

Methods

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(@_);
   }
 
 

AUTHOR

Original code by Damian Conway.

Maintained by Michael G Schwern until September 2005.

Now maintained by Tony Bowden.

BUGS and QUERIES

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.

SEE ALSO

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