Not sure what you mean. In Ruby, for instance, whenever a module is mixed in a hook method on the module is called. You can enforce any safety or correctness co

Not sure what you mean. In Ruby, for instance, whenever a module is mixed in a hook method on the module is called. You can enforce any safety or correctness constraints on the parent class that you want at that point. You can easily imagine writing a library in ruby that lets you do the same things as in Moose in terms of correctness and safety. Similarly, you could write your own 'include' method that took extra parameters and performed the same mixin magic Moose is doing like excluding or aliasing methods, performing special handling of conflicting methods, etc. My main point in all this is that, from my perspective, Moose may have a few bells and whistles beyond the base OO features of other dynamic languages, but these features are more 'nice to haves' than 'essentials. More importantly, these features could also be trivially added in other languages as libraries. Most importantly of all, none of these features is as important as starting out with a clean, well-designed language in the first place, and Perl is anything but clean or well-designed.