Moose::Cookbook::Extending::Recipe2(3)			User Contributed Perl Documentation		    Moose::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
";
	 };

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 v5.12.5							    2011-09-06				    Moose::Cookbook::Extending::Recipe2(3)