[Arnavion]

As I wrote in https://news.ycombinator.com/item?id=44048391 , you have to get used to copying the libstd impl when working with MaybeUninit. For my code I put a "TODO(rustup)" comment on such copies, to remind myself to revisit them every time I update the Rust version in toolchain.toml

[nemothekid]

In other words the """safe""" stable code looks like this:

    let mut data = Vec::with_capacity(sz);
    let mut dst_uninit = data.spare_capacity_mut();
    let uninit_src: &[MaybeUninit<T>] = unsafe { transmute(buf) };
    dst_uninit.copy_from_slice(uninit_src);
    unsafe { data.set_len(sz) };

[Arnavion]

That's correct.