Ownership and Borrowing

The sacred rules of ownership guide all Rustaceans.

§The Three Rules of Ownership

1. Each value in Rust has a variable that's called its owner
2. There can only be one owner at a time
3. When the owner goes out of scope, the value will be dropped

§Borrowing

You may borrow references without taking ownership:

fn calculate_length(s: &String) -> usize {
    s.len()
}

§Mutable References

Mutable references allow modification, but with restrictions:

fn append_text(s: &mut String) {
    s.push_str(" - blessed by the compiler");
}

"In Rust, you cannot have both a mutable reference and an immutable reference in the same scope."

§The Borrow Checker

The borrow checker ensures memory safety at compile time. Trust in its wisdom, for it prevents data races and use-after-free errors.

§Practice

Try writing functions that borrow references and see the borrow checker guide you to safe code.