Ownership and Borrowing

Mutable Borrow

Changing Through a Reference

A mutable reference (&mut) lets a function change a value the caller owns. Dereferencing with * reaches the value.

Program

Play the program to add a bonus to total through a mutable reference.

mutable_borrow.rs 
fn main() {
    let mut total = 10;
    add_bonus(&mut total);
    println!("{total}");
}

fn add_bonus(value: &mut i32) {
    *value += 5;
}
&mut `&mut total` hands out a mutable reference.
dereference `*value` reaches the value the reference points to.
in-place change The owned `total` reflects the change after the call.