I disagree about the main reason for wanting them. They may have been created to solve inheritance issues, but based on how often I'm asked about how to create private and read-only attributes, that seems to be the primary reason many people would want inside-out objects.
Oh I don't know. I would guess that people who want private and read-only attributes are just used to "strict" languages. I have hardly ever found them useful, since I'm of the opinion that you shouldn't access attributes from outside the object at all (i.e. you always want accessors or other methods to set the usefull attributes anyway), and if someone does
validate the encapsulation, it's his problem. In other words, from "the outside", the actual storage mechanism of attributes is not usually relevant, since you normally never access them directly anyway.
When I use inside-out
objects attributes it's when I know I'm going to have many differing inheriting classes. Especially mixing pure-perl and perl/XS code. That's where the safety is relevant - you don't want to overwrite some super/subclasses' internal data - which can be easy to do by accident if you don't know all the internals of your superclass, and if you're subclassing an XS class you usually don't even have a hash-based implementation anyway.