/ 
Class-Data-Accessor-0.01
River stage two • 19 direct dependents • 97 total dependents
/ Class::Data::Accessor

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_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');


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.

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