Moose::Cookbook::Legacy::Debugging\_BaseClassReplacement(3) User Contributed Perl Documentation Moose::Cookbook::Legacy::Debugging\_BaseClassReplacement(3)

# [SYNOPSIS](#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](#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](#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](#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.

2026-08-29 perl v5.44.0

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Document: Moose::Cookbook::Legacy::Debugging_BaseClassReplacement(3pm) from perl-moose 2.4000-r4 (Chainguard OS)
Source: https://github.com/moose/Moose