trusty (3) Moose::Cookbook::Extending::Debugging_BaseClassRole.3pm.gz

NAME

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

VERSION

       version 2.1005

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

       Moose is maintained by the Moose Cabal, along with the help of many contributors. See "CABAL" in Moose
       and "CONTRIBUTORS" in Moose for details.

COPYRIGHT AND LICENSE

       This software is copyright (c) 2013 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 v5.18.1                                       2013-Moose::Cookbook::Extending::Debugging_BaseClassRole(3pm)