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

impl<T: AsRef<[u32]>> Foo for T {
    fn foo(&self) -> u32 {
        self.as_ref()[0]
    }
}

fn bar<T>(f: T) -> u32
where
    T: Foo,
{
    f.foo() + 1
}

fn main() {
    let f: &[u32] = &[42];
    bar(f);
    let v = vec![34, 12];
    bar(&v);
}