References in Rust

Previous: Rust

Rules of references in Rust

• At any given time, you can have either one mutable reference or any number of immutable references.
• References must always be valid.

A reference in Rust never owns the value it points to; it only provides access to it. This ties references directly into Rust’s ownership system: borrowing values instead of transferring ownership. The act of creating a reference is called borrowing.

The borrow checker ensures that multiple immutable references can coexist, but a mutable reference must always be unique. This enforces Rust’s principle of immutability by default, consistent with `let` (immutable) and `mut` (mutable) bindings.

In terms of C++ comparison, &mut T behaves similarly to an lvalue reference (T&), while &T is closer to a const lvalue reference (T const&). The critical difference is that Rust enforces aliasing and lifetime guarantees at compile time, eliminating undefined behavior from dangling or aliased references.