You think?
The article is a train wreck of analysis piled on the train wreck of "OO Design", which is itself a train wreck of an attempt to promote reuse by modeling code with data types, which is itself a train wreck of an attempt to imagine what hypothetical programmers in some hypothetical universe might find "useful" as masturbatory aids, hypothetically speaking. (This is not actually true - OO[D] is really an attempt to commoditize programming.) Most of the comments here are just dumping more trains on the pile. The abstraction shitheap is so high at this point that we can barely even remember that we are supposed to be solving some kind of actual problem.
The best part of the article is when the author acknowledges that the code might not actually need to be thread safe and so avoids wasting his time with that particular assumption. There is nothing else to be salvaged. A square is not a rectangle? Goodbye mathematics - what is the point of a type system again? More to the point: what planet are the users of this API from? Obviously not this one, and just as obviously no one knows or cares. Not ONCE does the author stop to wonder what services the actual users actually need; it's only about what this guy thinks MIGHT comply with some random "design" rules. One wonders if the users even exist as anything other than just another abstraction, and wondering about what problems those users might actually be trying to solve is right out.
Object Oriented Design can be seen as a case of reusing a cliche and butchering it at the same time, with the cliche being the shooting of ones self in the foot, and the butchery being the placement of said foot squarely upon the face of beauty immediately before pulling the trigger.