Two rules references in Rust

TIL

633

Giang Nguyen viết ngày 01/10/2016

Rule 1

Can one or more immutable references (&T) to a resource

    fn main() {
        let x: i32 = 10;
        let y = &x;
        let z = &x;
        println!("{}", x);
    }

Output: 10;

Rule 2

Exactly one mutable reference (&mut T) to a resource

fn main() {
    let mut x = 10;
    let y = &mut x;
    println!("{}", x);
}

Compile error:

error[E0502]: cannot borrow `x` as immutable because it is also borrowed as mutable
 --> src/main.rs:4:20
  |
3 |     let y = &mut x;
  |                  - mutable borrow occurs here
4 |     println!("{}", x);
  |                    ^ immutable borrow occurs here
5 | }
  | - mutable borrow ends here