I haven't used something like that before, but I can see another way to accomplish the same thing. But I have no idea which one is the 'best'... (nor do I know if it works for the full 100%, I only did some basic testing)

Create a package to which you can tie a hash, add the restrictions/additions to in the STORE/FETCH method.

Now you could tie a hash in your new-function to that package, and return a blessed reference to the tied hash.

Now you could access the attributes as $self->{'attr'}, and the addition(s) as $self->{'rand120'} (for example ofc).

Have you considered using this/a similar technique?

(Note, I know that this wasn't your question but I thought it could be relevant/useful so I posted it...)