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,
$obj->Suitcase; # will return Purple
but
Pere::Ubu->Suitcase; # will still return Samsonite
If you don't want this behaviour use Class::Data::Inheritable instead.
Methods
mk_classaccessor
Class->mk_classaccessor($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(@_);
}
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.
[email protected] or bug me on irc.perl.org, nick mst
[email protected] 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
