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Manual Reference Pages  -  CLASS::MAKEMETHODS::EMULATOR::INHERITABLE (3)

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NAME

Class::MakeMethods::Emulator::Inheritable - Emulate Class::Inheritable

CONTENTS

SYNOPSIS



  package Stuff;
  use base qw(Class::MakeMethods::Emulator::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);



DESCRIPTION

This module is an adaptor that provides emulatation of Class::Data::Inheritable by invoking similiar functionality provided by Class::MakeMethods::ClassInherit.

The public interface provided by Class::MakeMethods::Emulator::Inheritable is identical to that of Class::Data::Inheritable.

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.

USAGE

As specified by Class::Data::Inheritable, clients should inherit from this module and then invoke the mk_classdata() method for each class method desired:



  Class->mk_classdata($data_accessor_name);



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.



  Class->mk_classdata($data_accessor_name, $initial_value);



You may also pass a second argument to initialize the 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(@_);
  }



COMPATIBILITY

Note that the internal implementation of Class::MakeMethods::ClassInherit does not match that of Class::Data::Inheritable. In particular, Class::Data::Inheritable installs new methods in subclasses when they first initialize their value, while

EXAMPLE

The example provided by Class::Data::Inheritable is equally applicable to this emulator.



  package Pere::Ubu;
  use base qw(Class::MakeMethods::Emulator::Inheritable);
  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 analgous 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);



SEE ALSO

See Class::MakeMethods for general information about this distribution.

See Class::MakeMethods::Emulator for more about this family of subclasses.

See Class::Data::Inheritable for documentation of the original module.

See perltootc for a discussion of class data in Perl.

See Class::MakeMethods::Standard::Inheritable and Class::MakeMethods::Template::ClassInherit for inheritable data methods.

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perl v5.20.3 MAKEMETHODS::EMULATOR::INHERITABLE (3) 2004-09-06

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