You are fundamentally misunderstanding the relationship between Rust's unique and shared mutabilities and the usual mutability in, say, C. The Rust equivalent o

You are fundamentally misunderstanding the relationship between Rust's unique and shared mutabilities and the usual mutability in, say, C. The Rust equivalent of C mutability is Cell. Conversely, the C equivalent of Rust's unique references is a `restrict` pointer. Cell is meant to be applied at the "leaves" of a type where individual assignments take place. When used this way, there is no additional copying relative to the straightforward C version. (Bringing up Vec and heap allocations here is also complete nonsense; Cell has nothing to do with Clone.) Once you wrap your head around that, all your shared mutability examples translate over to Rust trivially. All the "sacrifices" in speed you are imagining are relative to `restrict`/`&mut T`, not the usual baseline of a simple mutable object.