Upcast pattern

upcast_pattern.rs

trait Upcast<DynTy: ?Sized> {
    fn up(&self) -> &DynTy;
}

trait UpcastA {
    fn up_a<'me>(&self) -> &(dyn A + 'me)
    where 
        Self: 'me;
}

trait A: UpcastA {
   fn a_method(&self) {
       eprintln!("a_method");
   } 
}

impl<T: A> UpcastA for T {
    fn up_a<'me>(&self) -> &(dyn A + 'me)
    where
        Self: 'me,
    {
        self
    }
}

impl<'me, T: ?Sized + UpcastA + 'me> Upcast<dyn A + 'me> for T {
    fn up(&self) -> &(dyn A + 'me) {
        self.up_a()
    }
}

trait B: A { }

fn foo(x: &dyn B) {
    bar(x.up())
}

fn bar(x: &dyn A) {
    
}