[USE WITH CAUTION, not reviewed] How the compiler drops trait objects in Rust

unsafe_magic.rs

use std::ptr::write;

#[derive(Clone, Copy, Debug)]
#[repr(C)]
struct FatPtr {
    ptr: *mut (),
    extra: *const (),
}

trait Foo {
}

struct Bar(usize);

impl Foo for Bar {
}

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

unsafe fn _dyn(foo: *mut Foo) {
    let fat = *(&foo as *const _ as *const FatPtr);
    let vtable = fat.extra as *const fn(*mut ()); // is this using the Rust ABI?
    (*vtable)(fat.ptr);
}

fn main() {
    let mut dst = [0usize; 1];
    unsafe {
        write(&mut dst as *mut _ as *mut Bar, Bar(5));
        _dyn(&mut dst as *mut _ as *mut Bar as *mut Foo);
    }
}