NAME
    Class::Data::Accessor - Inheritable, overridable class and instance data
    accessor creation

SYNOPSIS
      package Stuff;
      use base qw(Class::Data::Accessor);

      # Set up DataFile as inheritable class data.
      Stuff->mk_classaccessor('DataFile');

      # Declare the location of the data file for this class.
      Stuff->DataFile('/etc/stuff/data');

      # Or, all in one shot:
      Stuff->mk_classaccessor(DataFile => '/etc/stuff/data');

      Stuff->DataFile; # returns /etc/stuff/data

      my $stuff = Stuff->new; # your new, not ours

      $stuff->DataFile; # returns /etc/stuff/data

      $stuff->DataFile('/etc/morestuff'); # sets it on the object

      Stuff->DataFile; # still returns /etc/stuff/data

DESCRIPTION
    Class::Data::Accessor is the marriage of Class::Accessor and
    Class::Data::Inheritable into a single module. It is used for creating
    accessors to class data that overridable in subclasses as well as in
    class instances.

    For example:

      Pere::Ubu->mk_classaccessor('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;

    Taking this one step further, you can make a subclass that 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');

    You can also override this class data on a per-object basis. If $obj isa
    Pere::Ubu then

      $obj->Suitcase; # will return Samsonite

      $obj->Suitcase('Purple'); # will set Suitcase *for this object only*

    And after you've done that,

      $obj->Suitcase; # will return Purple

    but

      Pere::Ubu->Suitcase; # will still return Samsonite

    If you don't want this behaviour use Class::Data::Inheritable instead.

    "mk_classaccessor" will die if used as an object method instead of as a
    class method.

METHODS
  mk_classaccessor
      Class->mk_classaccessor($data_accessor_name);
      Class->mk_classaccessor($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_classaccessor 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(@_);
      }

    Overriding accessors does not work in the same class as you declare the
    accessor in. It only works in subclasses due to the fact that
    subroutines are loaded at compile time and accessors are loaded at
    runtime, thus overriding any subroutines with the same name in the same
    class.

  mk_classaccessors(@accessornames)
    Takes a list of names and generates an accessor for each name in the
    list using "mk_classaccessor".

AUTHORS
    Based on the creative stylings of Damian Conway, Michael G Schwern, Tony
    Bowden (Class::Data::Inheritable) and Michael G Schwern, Marty Pauley
    (Class::Accessor).

    Coded by Matt S Trout Tweaks by Christopher H. Laco.

BUGS and QUERIES
    If your object isn't hash-based, this will currently break. My
    modifications aren't exactly sophisticated so far.

    mstrout@cpan.org or bug me on irc.perl.org, nick mst claco@cpan.org or
    irc.perl.org, nick claco

LICENSE
    This module is free software. It may be used, redistributed and/or
    modified under the terms of the Perl Artistic License (see
    http://www.perl.com/perl/misc/Artistic.html)

SEE ALSO
    perltootc has a very elaborate discussion of class data in Perl.
    Class::Accessor, Class::Data::Inheritable

