#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(derive_coerce_pointee)]
use std::marker::CoercePointee;
use std::ops::Deref;
#[derive(CoercePointee)]
#[repr(transparent)]
struct MySmartPointer<T: ?Sized>(Box<T>);
impl<T: ?Sized> Deref for MySmartPointer<T> {
    type Target = T;
    fn deref(&self) -> &T {
        &self.0
    }
}
trait MyTrait {}
impl MyTrait for i32 {}
fn main() {
    let ptr: MySmartPointer<i32> = MySmartPointer(Box::new(4));
    let ptr: MySmartPointer<dyn MyTrait> = ptr;
}