mod private {
    pub struct Foo {
        field: i32,
        bar: Bar,
    }

    pub struct Bar {
        pub field: u32,
    }

    impl std::ops::Deref for Foo {
        type Target = Bar;

        fn deref(&self) -> &Self::Target {
            &self.bar
        }
    }
}

use private::Foo;

fn example(f: Foo) {
    let a: i32 = f.field;
}

fn main() {}