use std::ptr;
use std::mem;

fn main() {
    let n: i32 = 394;

    let a_ptr: *const i32 = &n as *const i32;
    let b_ptr: *const i32 = ptr::null();

    let a_opt: Option<&i32> = unsafe { mem::transmute(a_ptr) };
    let b_opt: Option<&i32> = unsafe { mem::transmute(b_ptr) };

    assert_eq!(a_opt, Some(&394));
    assert_eq!(b_opt, None);
}