experiments.rs

use std::convert::Into;
use std::error::Error;

pub trait MyTrait<T> {
    type E: Into<Box<dyn Error>>;
    fn method(&self, _: T);

    fn boxed(self) -> Box<dyn MyTrait<T, E = Self::E>>
    where
        Self: Sized + 'static,
    {
        Box::new(self)
    }
}

impl<T, E> MyTrait<T> for Box<dyn MyTrait<T, E = E>>
where
    E: Into<Box<dyn Error>>,
{
    type E = E;
    fn method(&self, t: T) {
        (**self).method(t)
    }

    fn boxed(self) -> Box<dyn MyTrait<T, E = E>> {
        self
    }
}

pub trait MyTraitRefInput<T>: for<'t> MyTrait<&'t T> {
    fn boxed(self) -> Box<dyn for<'t> MyTrait<&'t T, E = <Self as MyTrait<&'t T>>::E>>
    where
        Self: Sized + 'static,
    {
        Box::new(self)
    }
}

struct Wrapper<T, E>(Box<dyn for<'t> MyTrait<&'t T, E = E>>);

impl<'t, T, E> MyTrait<&'t T> for Wrapper<T, E>
where
    E: Into<Box<dyn Error>>,
{
    type E = E;
    fn method(&self, t: &'t T) {
        self.0.method(t)
    }

    fn boxed(self) -> Box<dyn for<'a> MyTrait<&'a T, E = Self::E>> {
        self.0
    }
}

impl<E, T> MyTraitRefInput<T> for Wrapper<T, E>
where
    E: Into<Box<dyn Error>>,
{
    fn boxed(self) -> Box<dyn for<'t> MyTrait<&'t T, E = E>> {
        self.0
    }
}