use std::ptr;
#[derive(Debug, Default)]
struct Foo {
    v: Vec<u32>,
}


fn zeroed<T>(item: &mut T) {
    let mut ptr = item as *mut _ as *mut u8;

    let mut n = 0;

    let untill = std::mem::size_of::<T>();

    while n as usize + 8 <= untill {
        unsafe {
            ptr::write(ptr.offset(n + 0), 0);
            ptr::write(ptr.offset(n + 1), 0);
            ptr::write(ptr.offset(n + 2), 0);
            ptr::write(ptr.offset(n + 3), 0);
            ptr::write(ptr.offset(n + 4), 0);
            ptr::write(ptr.offset(n + 5), 0);
            ptr::write(ptr.offset(n + 6), 0);
            ptr::write(ptr.offset(n + 7), 0);
        }

        n += 8;
    }

    println!("Status after unrolled loop: n = {}, size_of::<T> = {}, bits = {}", n, untill, n * 8);

    for offset in n..untill as isize {
        println!("fixup loop round {}", offset);
        unsafe {
            ptr::write(ptr.offset(n + offset), 0);
        }
    }
}
fn main() {
    let mut f = Foo {
        v: Vec::new(),
    };

    zeroed(&mut f);
    println!("{:?}", f);

    println!("{:?}", f.v);

    for i in 0..100 {
        f.v.push(i);
    }

    println!("{:?}", f.v);

}