struct Foo<'a> {
    r:&'a str,
}

impl<'a> Foo<'a> {
    fn new(s: &'a str) -> Foo<'a> {
        Foo {
            r:s
        }
    }
}

#[derive(Default)]
struct Foos<'s> {
    r: Vec<&'s str>
}

impl<'s> Foos<'s> {
    fn add<'a : 's>(&mut self, f: Foo<'a>) {

        self.r.push(f.r);
    }
}

fn main() {
    let mut foos = Foos::<'static>::default();
    foos.add(Foo::new("foo"));
}