Comment by dwattttt

It's relevant when you have more complex objects, such as ones that contain independent mutexes that lock different sections of data.

You want the object to present its valid operations, but the object could also be constructed in single or multithreaded situations.

So you'd offer two APIs; one which requires a shared reference, and internally locks, and a second which requires a mutable reference, but does no locking.

Internally the shared reference API would just lock the required mutexes, then forward to the mutable reference API.