Moose::Cookbook::Legacy::Debugging_BaseClassReplacement - Providing an alternate base object class |
Moose::Cookbook::Legacy::Debugging_BaseClassReplacement - Providing an alternate base object class
version 2.1605
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' ); }
WARNING: Replacing the base class entirely, as opposed to applying roles to the base class, is strongly discouraged. This recipe is provided solely for reference when encountering older code that does this.
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 the Moose::Exporter manpage. 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 the Moose::Exporter manpage docs for more details on its API.
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;
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.
Moose is maintained by the Moose Cabal, along with the help of many contributors. See Moose/CABAL and Moose/CONTRIBUTORS for details.
This software is copyright (c) 2012 by Infinity Interactive, Inc..
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.
This software is copyright (c) 2006 by Infinity Interactive, Inc.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.
Moose::Cookbook::Legacy::Debugging_BaseClassReplacement - Providing an alternate base object class |