Moose::Cookbook::Extending::Debugging_BaseClassRole - Providing a role for the base object class |
Moose::Cookbook::Extending::Debugging_BaseClassRole - Providing a role for the base object class
version 2.1605
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"; };
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 the Moose::Exporter manpage and
the Moose::Util::MetaRole manpage, 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.
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.
Moose::Cookbook::Extending::Debugging_BaseClassRole - Providing a role for the base object class |