Is writing over a not deinitialized object undefined behavior?

Question

struct C { ... }
impl C {
  pub fn new() { ... }
}
fn main() {
  let mut x = C::new();
  unsafe { *(&x as *mut C) = C::new(); } // We are overwriting an object without disposing old value.
}

Is it undefined behavior?

If it is, how should I dispose the old object (x) before the unsafe assignment?

Answer 1

It is not undefined bevaviour

struct C;
impl C {
    pub fn new() -> Self {
        C
    }
}

impl Drop for C {
    fn drop(&mut self) {
        println!("C is Drop!");
    }
}

fn main() {
    let mut x = C::new();
    println!("before reassignment !");
    unsafe {
        *(&mut x as *mut C) = C::new();
    } // We are overwriting an object without disposing old value.
    println!("after reassignment !");
}

will print:

before reassignment !
C is Drop!
after reassignment !
C is Drop!