What Is Borrowing in Rust? Immutable References Explained

Borrowing in Rust is the mechanism that allows you to use a value without taking ownership of it, and an immutable reference (&T) lets you read that data without changing it. You create an immutable reference by prefixing a variable with &, which grants read-only access while the original owner retains control.

fn main() {
    let s1 = String::from("hello");
    let s2 = &s1; // Borrow s1 immutably
    println!("{s1}, {s2}");
}

You can have multiple immutable references to the same data at the same time, but you cannot modify the data through any of them.

Borrowing is like lending a book to a friend: they can read it, but they cannot tear out pages or write in it, and they must return it when they are done. This ensures the original owner keeps their copy safe while others use it. You use this whenever you need to pass data to a function or share it across your code without copying the entire thing.