phpman > perldoc > Moose::Cookbook::Legacy::Debugging_BaseClassReplacement

NAME
    Moose::Cookbook::Legacy::Debugging_BaseClassReplacement - Providing an alternate base object
    class

VERSION
    version 2.2200

SYNOPSIS
      package MyApp::Base;
      use Moose;

      extends 'Moose::Object';

      before 'new' => sub { warn "Making a new " . $_[0] };

      no Moose;

      package MyApp::UseMyBase;
      use Moose ();
      use Moose::Exporter;

      Moose::Exporter->setup_import_methods( also => 'Moose' );

      sub init_meta {
          shift;
          return Moose->init_meta( @_, base_class => 'MyApp::Base' );
      }

DESCRIPTION
    WARNING: Replacing the base class entirely, as opposed to applying roles to the base class, is
    strongly discouraged. This recipe is provided solely for reference when encountering older code
    that does this.

    A common extension is to provide an alternate base class. One way to do that is to make a
    "MyApp::Base" and add "extends 'MyApp::Base'" 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
    "MyApp::Base" for you.

    Then, instead of writing "use Moose" you can write "use MyApp::UseMyBase".

    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.

    This uses the magic of Moose::Exporter. When we call "Moose::Exporter->setup_import_methods(
    also => 'Moose' )" it builds "import" and "unimport" methods for you. The "also => 'Moose'" bit
    says that we want to export everything that Moose does.

    The "import" method that gets created will call our "init_meta" method, passing it "for_caller
    => $caller" as its arguments. The $caller is set to the class that actually imported us in the
    first place.

    See the Moose::Exporter docs for more details on its API.

USING MyApp::UseMyBase
    To actually use our new base class, we simply use "MyApp::UseMyBase" *instead* of "Moose". We
    get all the Moose sugar plus our new base class.

      package Foo;

      use MyApp::UseMyBase;

      has 'size' => ( is => 'rw' );

      no MyApp::UseMyBase;

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.

AUTHORS
    *   Stevan Little <stevan AT cpan.org>

    *   Dave Rolsky <autarch AT urth.org>

    *   Jesse Luehrs <doy AT cpan.org>

    *   Shawn M Moore <sartak AT cpan.org>

    *   יובל קוג'מן (Yuval Kogman) <nothingmuch AT woobling.org>

    *   Karen Etheridge <ether AT cpan.org>

    *   Florian Ragwitz <rafl AT debian.org>

    *   Hans Dieter Pearcey <hdp AT cpan.org>

    *   Chris Prather <chris AT prather.org>

    *   Matt S Trout <mstrout AT cpan.org>

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.