Mastering Rust - Second Edition

Borrowing rules

Similar to the ownership rule, we also have borrowing rules that maintain the single ownership semantics with references, too. These rules are as follows:

• A reference may not live longer than what it referred to. This is obvious, since if it did, it would be referring to a garbage value.
• If there's a mutable reference to a value, no other references, either mutable or immutable references, are allowed to the same value in that scope. A mutable reference is an exclusive borrow.
• If there is no mutable reference to a thing, any number of immutable references to the same value are allowed in the scope.

The borrowing rules in Rust are analyzed by a component of the compiler called the borrow checker. The Rust community amusingly ...