use std::any::Any;

trait T {
    fn foo(&self) -> &'static str;
    fn into_any(self: Box<Self>) -> Box<dyn Any>;
}

struct A();

impl T for A {
    fn foo(&self) -> &'static str {
        "a"
    }

    fn into_any(self: Box<Self>) -> Box<dyn Any> {
        self
    }
}

fn main() {
    // construct Box<dyn T>
    let a: Box<dyn T> = Box::new(A());
    println!("{}", a.foo());

    // convert Box<A> to Box<dyn Any>
    let a: Box<A> = Box::new(A());
    let a = a as Box<dyn Any>;
    println!("{}", a.downcast::<A>().unwrap().foo());

    // convert Box<dyn T> to Box<dyn Any>
    let a: Box<dyn T> = Box::new(A());
    let a = a.into_any();
    println!("{}", a.downcast::<A>().unwrap().foo());
}