What Is Mutable Borrowing in Rust?

Mutable borrowing in Rust is the act of creating a reference to a value that allows you to modify it, using the &mut syntax. You can only have one mutable reference to a particular piece of data in a particular scope at a time, and you cannot have a mutable reference while an immutable reference exists. This rule prevents data races and ensures memory safety at compile time.

fn main() {
    let mut number = 5;
    let mutable_ref = &mut number;
    *mutable_ref = 6; // Modifies the original value
    println!("{number}"); // Prints 6
}

Mutable borrowing is like borrowing a library book with a special pen that lets you write in it. While you have the book, no one else can read it or borrow it, ensuring no one else changes the pages while you are writing. This rule prevents conflicts where two people try to edit the same document at the same time.