Tracking issue for viewing Result/Option as slices

[alexcrichton]

This is a tracking issue for the unstable as_slice feature in the standard library. These functions enable viewing a Result<T, U> and Option<T> as some form of [T] (both shared and mutably). In each case an array of at most one item will be returned.

It's somewhat unclear (like with ref_slice and ref_mut_slice) how useful these are and whether they should exist to me.

[nagisa]

These can be trivially implemented in terms of ref_slice and ref_mut_slice.

[SimonSapin]

Which in turn can be trivially implemented in terms of slice::from_raw_parts{,_mut}, although with unsafe code. #27774

[alexcrichton]

This feature is now entering its final comment period for deprecation

[devonhollowood]

This seems like it could be pretty useful in some niche scenarios, although admittedly I haven't personally run into any of those niches. It seems useful enough though that I'm not sure that this should be deprecated.

[aturon]

As usual, I think there's little harm in providing additional conversions that follow the usual conventions.