simple examples of passing values by reference and references by reference

references_by_reference.rs

#[derive(Debug)]
struct Foo {
    n: u32,
}


fn overwrite<T: Copy>(input: &mut T, new: &mut T) {
    // FORBIDDEN: you will copy the pointer pointing to a future freed memory
    // *input = *new;
}

fn main() {
    let foo_long = Box::new(Foo { n: 1 });

    let mut foo_long_ref = &foo_long;

    {
        let foo_short = Box::new(Foo { n: 2 });
        let mut foo_short_ref = &foo_short;

        // The args are passed as References by Reference
        overwrite(&mut foo_long_ref, &mut foo_short_ref);
    }
    println!("{:?}", foo_long_ref);


}

values_by_reference.rs

#[derive(Copy, Clone, Debug)]
struct Foo {
    n: u32,
}


fn overwrite<T: Copy>(input: &mut T, new: &mut T) {
    // you are copying bits, it is safe
    *input = *new;
}

fn main() {
    let mut foo_long = Foo { n: 1 };

    {
        let mut foo_short = Foo { n: 2 };

        // The args are passed as Values by Reference
        overwrite(&mut foo_long, &mut foo_short);
    }
    println!("{:?}", foo_long);


}