fn main() {
    println!("Hello, world!");
    let vv = 1;
    println!("Before  {}", vv);
    rec_refr_mut_value(&vv);  // NOTE, do not have to label as mut
    println!("After   {}", vv);

    let mut vv = 1;
    println!("\n\nBefore  {}", vv);
    rec_refr_mut_reference(&mut vv);  // NOTE, MUST label as mut
    println!("After   {}", vv);
}

fn rec_refr(aa : &i32) {
    //*aa = 12;  //not allowed when behind a &
    // aa = &12; // cannot mutate aa
}

// this changes what the parameter points at, NOT
// what the original points at
fn rec_refr_mut_value(mut aa : &i32) {
    println!("Before  int {}", aa);
    //*aa = 12;  //not allowed when behind a &
    aa = &12; // cannot mutate aa
    println!("After  int {}", aa);
}

// in this version can mutate the value pointed to by the parameter
fn rec_refr_mut_reference(aa : &mut i32) {
    println!("Before  int {}", aa);
    *aa = 12;  //not allowed when behind a &
    //aa = &12; // cannot mutate aa
    println!("After  int {}", aa);
}


#[derive(Debug)]
struct aa {
    aval : i32
}

fn main2() {
    println!("Hello, world!");
    let vv = aa{aval:12};
    println!("Before  {:?}", vv);
    rec_refr_mut_value_s(&vv);  // NOTE, do not have to label as mut
    println!("After   {:?}", vv);

    let mut vv = aa{aval:12};
    println!("\n\nBefore  {:?}", vv);
    rec_refr_mut_reference_s(&mut vv);  // NOTE, MUST label as mut
    println!("After   {:?}", vv);
}

fn rec_refr_s(aa : &aa) {
    //*aa = 12;  //not allowed when behind a &
    // aa = &12; // cannot mutate aa
}

// this changes what the parameter points at, NOT
// what the original points at
fn rec_refr_mut_value_s(mut aa : &aa) {
    println!("Before  int {:?}", aa);
    //*aa = 12;  //not allowed when behind a &
    aa.aval = 12; // cannot mutate aa
    println!("After  int {:?}", aa);
}

// in this version can mutate the value pointed to by the parameter
fn rec_refr_mut_reference_s(mut aa : &aa) {
    println!("Before  int {:?}", aa);
    let mut bb = aa{aval:42};  //not allowed when behind a &
    aa = &bb; // compile error : `bb` does not live long enough
              // `bb` dropped here while still borrowed
    //aa = &12; // cannot mutate aa
    println!("After  int {:?}", aa);
}