Moose::Cookbook::Extending::Recipe3(3pm)
NAME
Moose::Cookbook::Extending::Recipe3 - Providing an alternate base
object class
SYNOPSIS
package MyApp::Base;
use Moose;
extends 'Moose::Object';
before 'new' => sub { warn "Making a new " . $_[0] };
no Moose;
package MyApp::UseMyBase;
use Moose ();
use Moose::Exporter;
Moose::Exporter->setup_import_methods( also => 'Moose' );
sub init_meta {
shift;
return Moose->init_meta( @_, base_class => 'MyApp::Base' );
}
DESCRIPTION
A common extension is to provide an alternate base class. One way to do
that is to make a "MyApp::base" and add "extends 'MyApp::Base'" to
every class in your application. That's pretty tedious. Instead, you
can create a Moose-alike module that sets the base object class to
"MyApp::Base" for you.
Then, instead of writing "use Moose" you can write
"use MyApp::UseMyBase".
In this particular example, our base class issues some debugging output
every time a new object is created, but you can think of some more
interesting things to do with your own base class.
This uses the magic of Moose::Exporter. When we call
"Moose::Exporter->setup_import_methods( also => 'Moose' )" it builds
"import" and "unimport" methods for you. The "also => 'Moose'" bit says
that we want to export everything that Moose does.
The "import" method that gets created will call our "init_meta" method,
passing it "for_caller => $caller" as its arguments. The $caller is set
to the class that actually imported us in the first place.
See the Moose::Exporter docs for more details on its API.
USING MyApp::UseMyBase
- To actually use our new base class, we simply use "MyApp::UseMyBase"
instead of "Moose". We get all the Moose sugar plus our new base class. - package Foo;
- use MyApp::UseMyBase;
- has 'size' => ( is => 'rw' );
- no MyApp::UseMyBase;
CONCLUSION
This is an awful lot of magic for a simple base class. You will often
want to combine a metaclass trait with a base class extension, and
that's when this technique is useful.
AUTHOR
Dave Rolsky <autarch@urth.org>
COPYRIGHT AND LICENSE
Copyright 2006-2010 by Infinity Interactive, Inc.
<http://www.iinteractive.com>
- This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.