struct UserInfo {
    id: i32,
    name: String,
    pass: String,
}

impl UserInfo {
    pub fn new(id: i32) -> UserInfo {
        UserInfo {
            id,
            name: format!("user{}", id),
            pass: String::from("***"),
        }
    }
}

fn register_user(user: &UserInfo) {
    println!("hello {}", user.name);
}

fn main() {
    let mut u1 = UserInfo::new(41);
    let mut u2 = UserInfo::new(43);
    unsafe {
        let ptr = &mut u2 as *mut UserInfo;
        std::ptr::write(ptr, u1);
    }
    register_user(&u2);
}