NAME
Moose::Cookbook::Extending::Recipe3 - Providing an alternate base object class
SYNOPSIS
package
MyApp::Base;
use
Moose;
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.
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 2006-2009 by Infinity Interactive, Inc.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.