NAME
Moose::Cookbook::Extending::Recipe2 - Providing a role for the base object class
SYNOPSIS
package
MooseX::Debugging;
use
Moose ();
use
Moose::Exporter;
Moose::Exporter->setup_import_methods;
sub
init_meta {
shift
;
my
%options
=
@_
;
my
$meta
= Moose->init_meta(
%options
);
Moose::Util::MetaRole::apply_base_class_roles(
for_class
=>
$options
{for_class},
roles
=> [
'MooseX::Debugging::Role::Object'
],
);
return
$meta
;
}
package
MooseX::Debugging::Role::Object;
use
Moose::Role;
after
'BUILD'
=>
sub
{
my
$self
=
shift
;
warn
"Made a new "
.
ref
$self
.
" object\n"
;
};
DESCRIPTION
In this example, we provide a role for the base object class that adds some simple debugging output. Every time an object is created, it spits out a warning saying what type of object it was.
Obviously, a real debugging role would do something more interesting, but this recipe is all about how we apply that role.
In this case, with the combination of Moose::Exporter and Moose::Util::MetaRole, we ensure that when a module does use MooseX::Debugging
, it automatically gets the debugging role applied to its base object class.
There are a few pieces of code worth looking at more closely.
Moose::Exporter->setup_import_methods;
This creates an import
method in the MooseX::Debugging
package. Since we are not actually exporting anything, we do not pass setup_import_methods
any parameters. However, we need to have an import
method to ensure that our init_meta
method is called.
Then in our init_meta
method we have this line:
Moose->init_meta(
%options
);
This is a bit of boilerplate that almost every extension will use. This ensures that the caller has a normal Moose metaclass before we go and add traits to it.
The Moose->init_meta
method does ensures that the caller has a sane metaclass, and we don't want to replicate that logic in our extension. If the Moose->init_meta
was already called (because the caller did use Moose
before using our extension), then calling Moose->init_meta
again is effectively a no-op.
AUTHOR
Dave Rolsky <autarch@urth.org>
COPYRIGHT AND LICENSE
Copyright 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.