Returning Box<dyn Self> via helper trait

as_trait.rs

trait Trait: AsTrait {
    fn get_answer(&self) -> i32;
}

struct S;

impl Trait for S {
    fn get_answer(&self) -> i32 { 42 }
}

trait AsTrait {
    fn as_trait(&self) -> &Trait;
}

impl<T> AsTrait for T where T: Trait {
    fn as_trait(&self) -> &Trait {
        self
    }
}

fn main() {
    let s = Box::new(S) as Box<dyn Trait>;
    let t = s.as_trait();
    println!("{}", t.get_answer());
}