What is the difference between immutable and mutable borrows

Immutable borrows (&T) let you read data without changing it, while mutable borrows (&mut T) let you modify the data but prevent any other borrows from existing at the same time.

fn main() {
    let mut number = 5;
    
    // Immutable borrow: can read, cannot write
    let immutable_ref = &number;
    println!("Read: {}", immutable_ref);
    
    // Mutable borrow: can read and write, exclusive access
    let mutable_ref = &mut number;
    *mutable_ref = 10;
    println!("Modified: {}", mutable_ref);
}

Think of an immutable borrow like reading a book in a library; you can look at it, but you can't write in it, and others can read it too. A mutable borrow is like checking out the only copy of a book; you can write in it, but no one else can touch it until you return it. This rule prevents crashes by ensuring only one person changes data at a time.