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 $self = shift->_self;
"$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 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 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.
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.
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.
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 persistent, so changes made to the
statically accessible object can be recovered later.
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 time.
No known bugs, but suggestions are welcome
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
Adam Kennedy <
[email protected]>
<
http://ali.as/>, 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.