use std::os::raw::c_void;

struct Counter {
    val: u32,
}

impl Counter {
    fn inc(&mut self, n: &mut N) {
        self.val += n.val;
        n.val += 1;
    }
}

struct N {
    val: u32,
}

struct X {
    n: N,
    ctr: Counter,
}

fn main() {
    let mut x = X{n: N{val:1}, ctr: Counter{val: 0}};

    {
        f(&mut x as *mut _ as *mut c_void);
        f(&mut x as *mut _ as *mut c_void);
    }

    println!("{}", x.ctr.val);
}

fn f(x_ptr: *mut c_void) {
    let x = unsafe { &mut *(x_ptr as *mut X) };
    x.ctr.inc(&mut x.n);
}