trait Foo {
    fn foo(&self) -> u32;
}

impl<'a> Foo for &'a [u32] {
    fn foo(&self) -> u32 {
        self[0]
    }
}

fn bar(f: impl Foo) -> u32 {
    f.foo()+1
}

fn main() {
    let f:&[u32] = &[42];
    println!("{}", bar(f));
}