use std::ops::Deref;

struct Big<'a> {
    option: BigOption,
    small: Small<&'a SmallOption>,
}

struct Small<T: Deref<Target = SmallOption>> {
    option: T,
}

struct BigOption {
    a: u32,
    small_option: SmallOption,
}

struct SmallOption {
    b: u32,
}

impl<T: Deref<Target = SmallOption>> Small<T> {
    fn new(option: T) -> Self {
        Self {
            option,
        }
    }
}

impl<'a> Big<'a> {
    fn new(option: BigOption) -> Self {
        let small = Small::new(&option.small_option);
        Self { option, small }
    }
}

fn main() {
    let big_option = BigOption {
        a: 123,
        small_option: SmallOption {
            b: 456,
        }
    };
    Big::new(big_option);
}