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Moose::Cookbook::Extending::Recipe2(3)ser Contributed Perl Documentationose::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 v5.12.5                                     2011-09-06           Moose::Cookbook::Extending::Recipe2(3)