NAME

       Moose::Cookbook::Extending::Debugging_BaseClassRole - Providing a role for the base object class

VERSION

       version 2.2009

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.

AUTHORS

       •   Stevan Little <stevan.little@iinteractive.com>

       •   Dave Rolsky <autarch@urth.org>

       •   Jesse Luehrs <doy@tozt.net>

       •   Shawn M Moore <code@sartak.org>

       •   יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>

       •   Karen Etheridge <ether@cpan.org>

       •   Florian Ragwitz <rafl@debian.org>

       •   Hans Dieter Pearcey <hdp@weftsoar.net>

       •   Chris Prather <chris@prather.org>

       •   Matt S Trout <mst@shadowcat.co.uk>

COPYRIGHT AND LICENSE

       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.

perl v5.26.1                                       2017-Moose::Cookbook::Extending::Debugging_BaseClassRole(3pm)