struct Foo<'a> {
    bar: &'a Bar,
}

impl<'a> Foo<'a> {
    const fn new(bar: &'a Bar) -> Foo<'a> {
        Foo { bar }
    }
}

struct Bar {
    value: i32,
}

impl Bar {
    const fn empty() -> Bar {
        Bar {
            value: 42,
        }
    }
}

fn main() {
    let foo = Foo::new(&Bar::empty());
    println!("{}", foo.bar.value);
}