Class::Data::Accessor - Inheritable, overridable class and instance data accessor creation 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 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
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(@_); } 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. 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 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) perltootc has a very elaborate discussion of class data in Perl. Class::Accessor, Class::Data::Inheritable