Rust: trait object with existential associated type

trait_object_associated_type.rs

// https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=c7d98a91435963f2cc8568b7dfd04366

use std::fmt::Debug;

trait MyTrait {
    type R: Debug;
    fn get_r(&self) -> Box<Self::R>;
}

#[derive(Debug)]
struct A;
impl MyTrait for A {
    type R = u32;
    fn get_r(&self) -> Box<Self::R> {
        Box::new(u32::default())
    }
}

#[derive(Debug)]
struct B;
impl MyTrait for B {
    type R = char;
    fn get_r(&self) -> Box<Self::R> {
        Box::new(char::default())
    }
}

struct AnyVecMyTrait<'a, D: Debug + 'a> {
    any_vec: Vec<&'a dyn MyTrait<R = D>>
}

impl<'a, D: Debug> AnyVecMyTrait<'a, D> {
    pub fn add<T: MyTrait<R = D>>(&mut self, a: &'a T) {
        self.any_vec.push(a);
    }

    pub fn debug_vec(self) {
        for v in self.any_vec.into_iter() {
            println!("{:?}", v.get_r());
        }
    }
}

#[test]
fn test_vec_of_dyn_object_with_associated_types() {
    let a = A;
    let b = B;
    let mut any_vec = AnyVecMyTrait {
        any_vec: vec!(),
    };
    any_vec.add(&a);
    any_vec.add(&b); // ERROR
    any_vec.debug_vec();
}