Deconstructing `Option<T>` in const context

2

Oh Map on non-copy option in const context mentions using:

const fn map_wrapper<T>(option: Option<T>) -> Option<Wrapper<T>> {
    match option {
        // call unwrap() instead of destructuring
        Some(_) => Some(Wrapper(option.unwrap())),

        // call forget() instead of dropping
        option @ None => {
            mem::forget(option);
            None
        }
    }
}

So we can avoid using unsafe:

const fn option_manually_drop<T>(value: Option<T>) -> Option<std::mem::ManuallyDrop<T>> {
    if value.is_some() {
        Some(std::mem::ManuallyDrop::new(value.unwrap()))
    } else {
        std::mem::forget(value);
        None
    }
}

const fn f<T>(slot: &mut MaybeUninit<T>, value: Option<T>) {
    if let Some(value) = option_manually_drop(value) {
        let value = std::mem::ManuallyDrop::into_inner(value);
        // use value somehow
        slot.write(value);
    }
}