#![feature(arbitrary_self_types)]
use std::marker::PhantomPinned;
use std::ops::Receiver;
use std::pin::Pin;

trait MyTrait {
    fn hello(self: Pin<&mut Foo<Self>>) -> Pin<&mut Foo<u32>>;
}
impl MyTrait for u32 {
    fn hello(self: Pin<&mut Foo<Self>>) -> Pin<&mut Foo<u32>> {
        self
    }
}

struct Foo<T: ?Sized> {
    _pin: PhantomPinned,
    val: T,
}

impl<T: ?Sized> Receiver for Foo<T> {
    type Target = T;
}
impl Unpin for Foo<dyn MyTrait> {}

fn pin_it(r: &mut Foo<u32>) -> Pin<&mut Foo<u32>> {
    Pin::<&mut Foo<dyn MyTrait>>::new(r).hello()
}