Class::Data::Accessor(3)

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
This module is now deprecated!

Please consider using Class::Accessor::Grouped or Moose

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 same terms as Perl itself. (see http://dev.perl.org/licenses/artistic.html and http://www.opensource.org/licenses/gpl-license.php)

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