Provided by: libclass-default-perl_1.51-3_all bug


       Class::Default - Static calls apply to a default instantiation


         # Create the defaulted class
         package Foo::Base;

         use base 'Class::Default';

         sub new { bless {}, $_[0] }

         sub show {
             my $self = shift->_self;

         # Do something to the default object

         package main;

         print Foo::Bar->show;

         # Prints 'Foo::Bar=HASH(0x80d22f8)'


       Class::Default provides a mechanism to allow your class to take static method calls and
       apply it to a default instantiation of an object. It provides a flexibility to an API that
       allows it to be used more confortably in different situations.

       A good example of this technique in use is When you use a static method, like
       "CGI-"header>, your call is being applied to a default instantiation of a CGI object.

       This technique appears to be especially useful when writing modules that you want to be
       used in either a single use or a persistent environment. In a CGI like environment, you
       want the simplicity of a static interface. You can call "Class-"method> directly, without
       having to pass an instantiation around constantly.


       Class::Default provides a couple of levels of control. They start with simple enabling the
       method to apply to the default instantation, and move on to providing some level of
       control over the creation of the default object.

   Inheriting from Class::Default
       To start, you will need to inherit from Class::Default. You do this in the normal manner,
       using something like "use base 'Class::Default'", or setting the @ISA value directly.
       "Class::Default" does not have a default constructor or any public methods, so you should
       be able to use it a multiple inheritance situation without any implications.

   Making method work
       To make your class work with Class::Default you need to make a small adjustment to each
       method that you would like to be able to access the default object.

       A typical method will look something like the following

         sub foobar {
             my $self = shift;

             # Do whatever the method does

       To make the method work with Class::Default, you should change it to the following

         sub foobar {
             my $self = shift->_self;

             # Do whatever the method does

       This change is very low impact, easy to use, and will not make any other differences to
       the way your code works.

   Control over the default object
       When needed, Class::Default will make a new instantation of your class and cache it to be
       used whenever a static call is made. It does this in the simplest way possible, by calling
       "Class-"new()> with no arguments.

       This is fine if you have a very pure class that can handle creating a new object without
       any arguments, but many classes expect some sort of argument to the the constructor, and
       indeed that the constructor that should be used it the "new" method.

       Enter the "_create_default_object" method. By overloading the "_create_default_object"
       method in your class, you can custom create the default object. This will used to create
       the default object on demand, the first time a method is called. For example, the
       following class demonstrate the use of "_create_default_object" to set some values in the
       default object.

         package Slashdot::User;

         use base 'Class::Default';

         # Constructor
         sub new {
               my $class = shift;
               my $name = shift;

               my $self = {
                       name => $name,
                       favourite_color => '',

               return bless $self, $class;

         # Default constructor
         sub _create_default_object {
               my $class = shift;

               my $self = $class->new( 'Anonymous Coward' );
               $self->{favourite_color} = 'Orange';

               return $self;

         sub name {

         sub favourite_color {

       That provides a statically accessible default object that could be used as in the
       following manner.

         print "The default slashdot user is " . Slashdot::User->name
             . " and they like the colour " . Slashdot::User->favourite_color;

       Remember that the default object is persistent, so changes made to the statically
       accessible object can be recovered later.

   Getting access to the default object
       There are a few ways to do this, but the easiest way is to simple do the following

         my $default = Slashdot::User->_get_default;


       Used by methods to make the method apply to the default object if called statically
       without affecting normal object methods.

       The "_class" method provides the opposite of the "_self" method. Instead of always getting
       an object, "_class" will always get the class name, so a method can be guaranteed to run
       in a static context. This is not essential to the use of a "Class::Default" module, but is
       provided as a convenience.

       Used to get the default object directly.

       To be overloaded by your class to set any properties to the default object at creation


       No known bugs, but suggestions are welcome


       Bugs should be reported via the CPAN bug tracker at


       For other issues, contact the author


       Adam Kennedy <>


       <>, Class::Singleton


       Copyright (c) 2002 - 2006 Adam Kennedy.

       This program is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

       The full text of the license can be found in the LICENSE file included with this module.