In this context, "unsynchronized access" refers to read/write operations happening concurrently on multiple threads, *not* to the shared pointers pointing to di

In this context, "unsynchronized access" refers to read/write operations happening concurrently on multiple threads, *not* to the shared pointers pointing to different objects as a result of the assignment. Unsynchronized access to the pointed to object will typically cause a specific kind of race condition called a data race, which is undefined behaviour. As it requires threads, it cannot happen in a single-threaded context.