InsideOutClass - A set of example metaclasses which implement the Inside-Out technique


  package Foo;

  use metaclass (
    ':attribute_metaclass' => 'InsideOutClass::Attribute',
    ':instance_metaclass'  => 'InsideOutClass::Instance'

  __PACKAGE__->meta->add_attribute('foo' => (
      reader => 'get_foo',
      writer => 'set_foo'

  sub new  {
      my $class = shift;

  # now you can just use the class as normal


This is a set of example metaclasses which implement the Inside-Out class technique. What follows is a brief explaination of the code found in this module.

We must create a subclass of Class::MOP::Instance and override the slot operations. This requires overloading get_slot_value, set_slot_value, slot_initialized, and initialize_slot, as well as their inline counterparts. Additionally we overload add_slot in order to initialize the global hash containing the actual slot values.

And that is pretty much all. Of course I am ignoring need for inside-out objects to be DESTROY-ed, and some other details as well (threading, etc), but this is an example. A real implementation is left as an exercise to the reader.


Stevan Little <>

Yuval Kogman <>


Copyright 2006-2008 by Infinity Interactive, Inc.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.