There are some cases were dynamic checks are required (e.g. with reference counting/shared ownership: class in Swift, Rc/Arc in Rust). Swift will automatically insert checks in these cases, whereas they have to be manually written into Rust code (via tools like RefCell). Swift and the APIs inherited from Obj-C use a lot more reference counting that Rust does by default, plus it's more difficult for the programmer to reason about the checks (e.g. to be able to write code that avoids them, to optimise) when they're implicit.
In summary, Rust and Swift have essentially the same rules, but Rust requires manual code to break the default rules, whereas the Swift compiler will implicitly insert those necessary checks (in some cases).
