// $ rustc ownersystem_4_mutable.rs 
// $ ./ownersystem_4_mutable
struct Bob {
    n: Vec<i32>
}

impl Bob {
    fn new() -> Bob {
        Bob { n: Vec::new() }
    }
}

fn func_1() {
    let mut n = Bob::new();
    let n1 = &mut n;
    // doesn't work because there is already a mutable borrowing
    //let n2 = &n;
    func_2(n1);
    //func_3(n2);
    //works because both func_2 and func_3 only got read only references
    println!("{}", n.n[0]);
}

fn func_2(b: &mut Bob) {
    println!("{}", b.n[0]);
}

fn func_3(b: &Bob) {
    println!("{}", b.n[0]);
}

fn main() {
    func_1();
}