phpMan > perldoc > Class::Data::Inheritable

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 overridden.

    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 overridden a method:

      # Raygun has an orange suitcase, Pere::Ubu's is still Blue.
      Raygun->Suitcase('Orange');

    Now that Raygun has overridden Pere::Ubu further 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 AT rt.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.