I think you are discussing different things, and in the process missing the whole point. It's one thing for an object to be immutable throughout is life cycle.

I think you are discussing different things, and in the process missing the whole point. It's one thing for an object to be immutable throughout is life cycle. That's immaterial to this discussion. It's an entirely different thing that the same object cannot be changed within specific contexts. If you want to ensure that a thread has read access to an object and it cannot be changed accidentally then passing a const reference to that object already ensures that. That's pretty much the whole point of const.