SYNOPSIS
# Create the defaulted class
package Foo::Base;
use base 'Class::Default';
sub new { bless {}, $_[0] }
sub show {
my $self = shift->_self;
"$self";
}
# Do something to the default object
package main;
print Foo::Bar->show;
# Prints 'Foo::Bar=HASH(0x80d22f8)'
DESCRIPTION
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 CGI.pm. 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 usefull when writing modules that you want to be used in either a single use or a persistant 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.
USING THE MODULES
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 {
$_[0]->_self->{name};
}
sub favourite_color {
$_[0]->_self->{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 persistant, 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;
METHODS
_self
Used by methods to make the method apply to the default object if called
statically without affecting normal object methods.
_class
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 guarenteed to run in a static context. This is not
essential to the use of a "Class::Default" module, but is provided as a
convenience.
_get_default
Used to get the default object directly.
_create_default_object
To be overloaded by your class to set any properties to the default object at creation time.
SUPPORT
Bugs should be reported via the CPAN bug tracker at<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Class-Default>
For other issues, contact the author