About invariants generally: Rust wants to know when memory behind each pointer is immutable, or mutable by Rust only, or could be mutated by something else whil

About invariants generally: Rust wants to know when memory behind each pointer is immutable, or mutable by Rust only, or could be mutated by something else while Rust has a pointer to it. Rust also encodes which types can't be moved to another thread, and which pointers own their memory and need to be freed by Rust. These are part of the type system, so they need to be defined precisely. The answer to these questions can't be just "it depends". If there are run-time or config-dependent conditions when the same data is owned or not or immutable or not, Rust has enums, unions and unsafe escape hatches to guard access to it.