Moose::Cookbook::ExtenUser:Contributed PMoose::Cookbook::Extending::Recipe2(3)NAME
Moose::Cookbook::Extending::Recipe2 - Providing a role for the base
object class
VERSION
version 2.0205
SYNOPSIS
package MooseX::Debugging;
use Moose::Exporter;
Moose::Exporter->setup_import_methods(
base_class_roles => ['MooseX::Debugging::Role::Object'],
);
package MooseX::Debugging::Role::Object;
use Moose::Role;
sub BUILD {}
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(
base_class_roles => ['MooseX::Debugging::Role::Object'],
);
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 related to exports, but we need
to have an "import" method to ensure that our "init_meta" method is
called. The "init_meta" is created by "setup_import_methods" for us,
since we passed the "base_class_roles" parameter. The generated
"init_meta" will in turn call
Moose::Util::MetaRole::apply_base_class_roles.
sub BUILD {}
after BUILD => sub {
...
};
Due to the way role composition currently works, if the class that a
role is composed into contains a "BUILD" method, then that will
override the "BUILD" method in any roles it composes, which is
typically not what you want. Using a method modifier on "BUILD" avoids
this issue, since method modifiers compose together rather than being
overridden. Method modifiers require that a method exists in order to
wrap, however, so we also provide a stub method to wrap if no "BUILD"
method exists in the class.
AUTHOR
Stevan Little <stevan@iinteractive.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 2011 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.
perl v5.12.52011-0Moose::Cookbook::Extending::Recipe2(3)
