Badger::Prototype - base class for creating prototype classes
package Badger::Example; use base 'Badger::Prototype'; sub greeting { my $self = shift; # get prototype object if called as a class method $self = $self->prototype() unless ref $self; # continue as normal, now $self is an object if (@_) { # set greeting if called with args return ($self->{ greeting } = shift); } else { # otherwise get greeting return $self->{ greeting }; } }
This module is a subclass of Badger::Base that additionally provides the prototype() method. It is used as a base class for modules that have methods that can be called as either class or object methods.
# object method my $object = Badger::Example->new(); $object->greeting('Hello World'); # class method Badger::Example->greeting('Hello World');
The prototype() method returns a singleton object instance which can be used as a default object by methods that have been called as class methods.
Here's an example of a greeting() method that can be called with an argument to set a greeting message:
greeting()
$object->greeting('Hello World');
Or without any arguments to get the current message:
print $object->greeting; # Hello World
As well as being called as an object method, we want to be able to call it as a class method:
Badger::Example->greeting('Hello World'); print Badger::Example->greeting(); # Hello World
Here's what the greeting() method looks like.
We use ref $self to determine if greeting() has been called as an object method ($self contains an object reference) or as a class method ($self contains the class name, in this case Badger::Example). In the latter case, we call prototype() as a class method (remember, $self contains the Badger::Example class name at this point) to return a prototype object instance which we then store back into $self.
ref $self
$self
Badger::Example
# get prototype object if called as a class method $self = $self->prototype() unless ref $self;
For the rest of the method we can continue as if called as an object method because $self now contains a Badger::Example object either way.
Note that the prototype object reference is stored in the $PROTOTYPE variable in the package of the calling object's class. So if you call prototype on a Badger::Example::One object that is subclassed from Badger::Prototype then the prototype object will be stored in the $Badger::Example::One::PROTOTYPE package variable.
$PROTOTYPE
Badger::Example::One
Badger::Prototype
$Badger::Example::One::PROTOTYPE
Constructor method to create a prototype object and cache it in the $PROTOTYPE package variable for subsequent use. This is usually called from inside methods that can operate as class or object methods, as shown in the earlier example.
sub example { my $self = shift; # upgrade $self to an object when called as a class method $self = $self->prototype() unless ref $self; # ...code follows... }
If you prefer a more succint idiom and aren't too worried about calling the prototype method unneccessarily, then you can write it like this:
sub greeting { my $self = shift->prototype; # ...code follows... }
If any arguments are passed to the prototype() method then it forces a new prototype object to be created, replacing any existing one cached in the $PROTOTYPE package variable. The arguments are forwarded to the new() constructor method called to create the object.
prototype()
new()
If a single undefined value is passed as an argument then any existing prototype is released by setting the $PROTOTYPE package variable to undef. The existing prototype is then returned, or undef if there was no prototype defined.
undef
Returns true or false to indicate if a prototype is defined for a class. It can be called as a class or object method.
Andy Wardley http://wardley.org/
Copyright (C) 2006-2009 Andy Wardley. All Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
To install Badger, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Badger
CPAN shell
perl -MCPAN -e shell install Badger
For more information on module installation, please visit the detailed CPAN module installation guide.