IntoBytes for MaybeUninit<T>

[kartva]

(not attaching the name of my project since it's still a prototype)

When building a zerocopy network protocol, I want to be able to have a function with the following signature:

pub unsafe fn send(&mut self, fill: impl FnOnce(&mut MaybeUninit<Payload>)) {
        let mem = &mut packet[packet_start_offset..];
        fill(MaybeUninit::<Payload>::mut_from_bytes(mem).unwrap());
        ...
}

so that users can just write to the uninit data and thus write to the underlying byte buffer.

Are there any reasons for why this isn't possible / desirable?

[kupiakos]

The reason this isn't directly possible is because one can pass this in for fill: |x| *x = MaybeUninit::uninit(), thus deinitializing previously initialized memory in packet.

You want something like "out" references:

use uninit::extension_traits::{AsOut, ManuallyDropMut};
use uninit::out_ref::Out;

pub unsafe fn send(&mut self, fill: impl FnOnce(Out<'_, Payload>)) {
        let payload = Payload::mut_from_bytes(&mut packet[packet_start_offset..]).unwrap();
        fill(MaybeUninit::<Payload>::mut_from_bytes(payload.manually_drop_mut().as_out()).unwrap());
        ...
}