struct Bar<'a> {
    c: &'a [u8],
}

impl<'a> Bar<'a> {
    fn new(c: &'a [u8]) -> Bar<'a> {
        Bar { c }
    }
}

struct Foo<'a> {
    a: &'a [u8],
    b: Bar<'a>,
}

impl<'a> Foo<'a> {
    fn new(a: &'a [u8]) -> Foo<'a> {
        let mut b = a.to_vec();
        b.push(4);
        Foo { a, b: Bar::new(&b) }
    }
}

fn main() {
    let foo = Foo::new(&[1, 2, 3]);
    println!("{:x?} {:x?}", foo.a, foo.b.c);
}