Rust doesn't have immutable memory, only access restrictions. An exclusive owner of an object can always mutate it, or can lend temporary read-only access to it

Rust doesn't have immutable memory, only access restrictions. An exclusive owner of an object can always mutate it, or can lend temporary read-only access to it. So the same memory may flip between exclusive-write and shared-read back and forth. It's an interesting optimization, but not something that could be done directly.