rust-ownership-patterns

E0382 occurs when a value is used after its ownership moved to another binding or function. Fix it by passing a reference with & instead of moving, calling .clone() to create an explicit deep copy, or restructuring the code so the original owner stays alive.

Use Rc for shared ownership in single-threaded code and Arc for shared ownership across threads. Use RefCell for interior mutability in single-threaded contexts, and Mutex or RwLock when mutation must be thread-safe.

Copy is an implicit bitwise duplicate limited to stack-only types like i32, f64, and bool, so assignment never moves. Clone is an explicit .clone() call that can perform deep copies of heap data like String and Vec.

Explicit <'a> annotations are required when the compiler's three elision rules cannot determine which input reference the output borrows from, such as functions taking two or more references. Structs holding references must always declare lifetime parameters.

E0499 happens because Rust allows only one &mut reference at a time to prevent data races. Fix it by narrowing the scope of each mutable borrow, splitting borrows across disjoint fields, or using RefCell for runtime borrow checking.

Use Cow<'_, str> when a function usually returns a borrowed slice but occasionally needs to allocate, such as normalization that only modifies some inputs. This avoids unnecessary heap allocations in the common borrowed case.