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.\"
.IX Title "Moose::Cookbook::Extending::Recipe3 3"
.TH Moose::Cookbook::Extending::Recipe3 3 "2009-05-01" "perl v5.8.7" "User Contributed Perl Documentation"
.SH "NAME"
Moose::Cookbook::Extending::Recipe3 \- Providing an alternate base object class
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  package MyApp::Base;
\&  use Moose;
.Ve
.PP
.Vb 1
\&  extends 'Moose::Object';
.Ve
.PP
.Vb 1
\&  before 'new' => sub { warn "Making a new " . $_[0] };
.Ve
.PP
.Vb 1
\&  no Moose;
.Ve
.PP
.Vb 3
\&  package MyApp::UseMyBase;
\&  use Moose ();
\&  use Moose::Exporter;
.Ve
.PP
.Vb 1
\&  Moose::Exporter\->setup_import_methods( also => 'Moose' );
.Ve
.PP
.Vb 4
\&  sub init_meta {
\&      shift;
\&      return Moose\->init_meta( @_, base_class => 'MyApp::Base' );
\&  }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
A common extension is to provide an alternate base class. One way to
do that is to make a \f(CW\*(C`MyApp::base\*(C'\fR and add \f(CW\*(C`extends\ 'MyApp::Base'\*(C'\fR to every class in your application. That's pretty
tedious. Instead, you can create a Moose-alike module that sets the
base object class to \f(CW\*(C`MyApp::Base\*(C'\fR for you.
.PP
Then, instead of writing \f(CW\*(C`use\ Moose\*(C'\fR you can write \f(CW\*(C`use\ MyApp::UseMyBase\*(C'\fR.
.PP
In this particular example, our base class issues some debugging
output every time a new object is created, but you can think of some
more interesting things to do with your own base class.
.PP
This uses the magic of Moose::Exporter. When we call \f(CW\*(C`Moose::Exporter\->setup_import_methods( also => 'Moose' )\*(C'\fR it builds
\&\f(CW\*(C`import\*(C'\fR and \f(CW\*(C`unimport\*(C'\fR methods for you. The \f(CW\*(C`also => 'Moose'\*(C'\fR
bit says that we want to export everything that Moose does.
.PP
The \f(CW\*(C`import\*(C'\fR method that gets created will call our \f(CW\*(C`init_meta\*(C'\fR
method, passing it \f(CW\*(C`for_caller => $caller\*(C'\fR as its
arguments. The \f(CW$caller\fR is set to the class that actually imported
us in the first place.
.PP
See the Moose::Exporter docs for more details on its \s-1API\s0.
.SH "USING MyApp::UseMyBase"
.IX Header "USING MyApp::UseMyBase"
To actually use our new base class, we simply use \f(CW\*(C`MyApp::UseMyBase\*(C'\fR
\&\fIinstead\fR of \f(CW\*(C`Moose\*(C'\fR. We get all the Moose sugar plus our new base
class.
.PP
.Vb 1
\&  package Foo;
.Ve
.PP
.Vb 1
\&  use MyApp::UseMyBase;
.Ve
.PP
.Vb 1
\&  has 'size' => ( is => 'rw' );
.Ve
.PP
.Vb 1
\&  no MyApp::UseMyBase;
.Ve
.SH "CONCLUSION"
.IX Header "CONCLUSION"
This is an awful lot of magic for a simple base class. You will often
want to combine a metaclass trait with a base class extension, and
that's when this technique is useful.
.SH "AUTHOR"
.IX Header "AUTHOR"
Dave Rolsky <autarch@urth.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
Copyright 2006\-2009 by Infinity Interactive, Inc.
.PP
<http://www.iinteractive.com>
.PP
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.