paste

// #![feature(trait_upcasting)]

use std::sync::Arc;

trait Foo: std::fmt::Display {
    fn a(&self) {
        println!("Foo::a -- {}", self);
    }
}

trait Bar: Foo {
    fn a(&self) {
        println!("Bar::a -- {}", self);
    }

    fn b(&self) {
        println!("Bar::b -- {}", self);
    }
}

impl Foo for i32 {}

impl Bar for i32 {}

fn main() {
    let bar: &dyn Bar = &21;
    let foo: &dyn Foo = bar;
    foo.a();
    println!("foo: {}", foo);
    Bar::a(bar);
    bar.b();

    let bar: Arc<dyn Bar> = Arc::new(42);
    println!("Arc-bar: {}", bar);
    let foo: Arc<dyn Foo> = bar;
    println!("Arc-foo: {}", foo);
}