trait Foo {
    const U: usize;
}

trait Bar {
    const V: usize;
}

impl<T: Foo> Bar for T {
    const V: usize = 5 - T::U;
}

impl Foo for u32 {
    const U: usize = 6;
}

fn main() {
    // uncomment for error
    //let x = <u32 as Bar>::V;
    //println!("{}", x);
}