Gotcha. I think, then, that the devil is in the details. That Erlang ets module I mentioned elsewhere does something like this, where it creates an entity that

Gotcha. I think, then, that the devil is in the details. That Erlang ets module I mentioned elsewhere does something like this, where it creates an entity that acts as a shared mutable data store, but communication with it still happens by message passing, so you still get certain guarantees. Notably, if you query it for some information and then get your response back, that response's contents aren't going to change on you. So the behavior's really more like querying a database than getting a pointer to a mutable data structure. There's maybe a "letter of the law vs spirit of the law" thing going on here, too. Having an object that just implements an array feels like it's violating the basic idea, even if you are technically only communicating with it by passing messages. I'm pretty sure the original vision was that objects would represent interesting entities from the business domain and not just be heavyweight analogues for basic data structures.