# Class::Data::Inheritable - phpMan

## 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@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.