Matthew Simon Cavalletto > Class-MakeMethods-1.009 > Class::MakeMethods::Emulator::Inheritable

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NAME ^

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

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);
  
  # Raygun's 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 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');

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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