pinned_but_unpinned.rs

use std::borrow::BorrowMut;
use std::convert::From;
use std::ops::Drop;
use std::pin::Pin;

#[derive(Debug)]
#[allow(dead_code)]
struct U8Wrapper(u8, ());
impl From<u8> for U8Wrapper {
    fn from(value: u8) -> Self {
        Self(value, Default::default())
    }
}
impl Drop for U8Wrapper {
    fn drop(&mut self) {
        println!("{self:?}@{self:p} dropped")
    }
}

fn main() {
    let mut value_a = U8Wrapper::from(3);
    let mut value_b = U8Wrapper::from(5);
    {
        let ref_a = &mut value_a;
        let ref_b = &mut value_b;
        println!();
        println!("ref_a: {}", std::any::type_name_of_val(&ref_a));
        println!("ref_b: {}", std::any::type_name_of_val(&ref_b));

        println!(
            "(ref_a, ref_b) @ ({0:p}, {1:p}) = ({0:?}, {1:?})",
            ref_a, ref_b
        );
        std::mem::swap::<U8Wrapper>(ref_a.borrow_mut(), ref_b.borrow_mut());
        println!("swap(ref_a, ref_b)");
        println!(
            "(ref_a, ref_b) @ ({0:p}, {1:p}) = ({0:?}, {1:?})",
            ref_a, ref_b
        );

        let mut ref_a = Pin::new(ref_a);
        let mut ref_b = Pin::new(ref_b);
        println!();
        println!("ref_a: {}", std::any::type_name_of_val(&ref_a));
        println!("ref_b: {}", std::any::type_name_of_val(&ref_b));

        println!(
            "(ref_a, ref_b) @ ({0:p}, {1:p}) = ({0:?}, {1:?})",
            ref_a, ref_b
        );
        std::mem::swap::<U8Wrapper>(ref_a.borrow_mut(), ref_b.borrow_mut());
        println!("swap(ref_a, ref_b)");
        println!(
            "(ref_a, ref_b) @ ({0:p}, {1:p}) = ({0:?}, {1:?})",
            ref_a, ref_b
        );
    }
    {
        let mut ref_a = Box::new(value_a);
        let mut ref_b = Box::new(value_b);
        println!();
        println!("ref_a: {}", std::any::type_name_of_val(&ref_a));
        println!("ref_b: {}", std::any::type_name_of_val(&ref_b));

        println!(
            "(ref_a, ref_b) @ ({0:p}, {1:p}) = ({0:?}, {1:?})",
            ref_a, ref_b
        );
        std::mem::swap::<U8Wrapper>(ref_a.borrow_mut(), ref_b.borrow_mut());
        println!("swap(ref_a, ref_b)");
        println!(
            "(ref_a, ref_b) @ ({0:p}, {1:p}) = ({0:?}, {1:?})",
            ref_a, ref_b
        );

        let mut ref_a = Pin::new(ref_a);
        let mut ref_b = Pin::new(ref_b);
        println!();
        println!("ref_a: {}", std::any::type_name_of_val(&ref_a));
        println!("ref_b: {}", std::any::type_name_of_val(&ref_b));

        println!(
            "(ref_a, ref_b) @ ({0:p}, {1:p}) = ({0:?}, {1:?})",
            ref_a, ref_b
        );
        std::mem::swap::<U8Wrapper>(ref_a.borrow_mut(), ref_b.borrow_mut());
        println!("swap(ref_a, ref_b)");
        println!(
            "(ref_a, ref_b) @ ({0:p}, {1:p}) = ({0:?}, {1:?})",
            ref_a, ref_b
        );
    }
}