Borrowing and References

Use values without taking ownership.

Learning objectives

• Create immutable references
• Create mutable references safely
• Understand borrowing rules

Borrowing

Borrowing allows a function or variable to use a value without taking ownership of it. This is done with references.

Immutable References

An immutable reference lets you read a value but not change it.

Mutable References

A mutable reference lets you change a value. Rust restricts mutable borrowing to prevent data races and conflicting changes.

Example code

fn print_length(text: &String) {
    println!("Length: {}", text.len());
}

fn add_word(text: &mut String) {
    text.push_str(" programming");
}

fn main() {
    let mut language = String::from("Rust");
    print_length(&language);
    add_word(&mut language);
    println!("{}", language);
}