mod thing {
    pub trait Tr {
        fn foo(&self) -> u32;
    }

    pub struct S;

    impl S {
        pub fn foo(&self) -> u32 {
            Tr::foo(self)
        }
    }

    impl Tr for S {
        fn foo(&self) -> u32 {
            1
        }
    }
}

fn main() {
    let s = thing::S;
    println!("{:?}", s.foo());
}