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Man Pages


Manual Reference Pages  -  CLASS::DATA::INHERITABLE (3)

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NAME

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

CONTENTS

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);
 
  # Rayguns 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 Rayguns and Pere::Ubus 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::Ubus 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 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.

SEE ALSO

perltooc has a very elaborate discussion of class data in Perl.
Search for    or go to Top of page |  Section 3 |  Main Index


perl v5.20.3 CLASS::DATA::INHERITABLE (3) 2008-01-25

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