We are finishing up a re-architecture of one of our internal applications. Most of the design inherits from an Inside-out object that we developed (Common::Thing). It uses blessed scalar refs as the object. Every class that inherits from this class also inherits new(), copy(), seed(), dump(), as_hash(), and DESTROY() object methods and a make_attributes() class method. Common::Thing does some stash manipulations to make a getter/setter method for each attribute in the derived class's name space. A derived class would look something like:

package My::Thing;

use base qw(Common::Thing);

__PACKAGE__->make_attributes( qw/ head should knees toes / );

# methods to do work go in here

1;
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It has worked well for our purposes, but certainly fails thread safety. We did quite a bit of work to stabalize our application around threads, but finally gave up when the fact that Perl is not thread-safe became overpoweringly obvious.