This is what keeps dragging me back to moose & perl5. You describe the attributes of a class, the constructor for that class is created for you, and you can pa

This is what keeps dragging me back to moose & perl5. You describe the attributes of a class, the constructor for that class is created for you, and you can pass in hashes and it will automatically instantiate (and fail if the rules you have set for attributes are not met). I've found that you can kinda sorta do the same with other languages (python/ruby/javascript) by writing static factory builders inside the class that do this checking for you and raise an exception or return an object for you, but it still doesn't compare to me to Moose/Moose::Util::TypeConstraints::coerce/subtype and attributes with the coerce option set. It makes it so easy to coerce a deep json object into a deep class structure. I always try to hunt down things that are similar in other languages (python allows named arguments from a dict, IIRC, and that allows similar things, but you still have to write the constructor yourself), but I've yet to find something that makes it as simple.