trait Functionality<T> {
    fn func(self, other: T);
}

trait Marker {}

impl<'a, T: Marker> Functionality<&'a Vec<T>> for &'a Vec<T> {
    fn func(self, other: &'a Vec<T>) {}
}

impl<'a, T> Functionality<&'a T> for &'a Vec<T> {
    fn func(self, other: &'a T) {}
}

struct Elem;

// Uncomment this impl for code to compile
// impl Marker for Elem {}

fn main() {
    let v = vec![Elem];
    v.func(&v);
}