Tracking Issue for Vec::spare_capacity_mut

[Amanieu]

The feature gate for the issue is #![feature(vec_spare_capacity)].

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also uses as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

Implementation history

• Initial implementation (Add Vec::spare_capacity_mut #75015)

[danielhenrymantilla]

FWIW, here is a full-featured API provided by an external crate: https://docs.rs/uninit/0.3.0/uninit/extension_traits/trait.VecCapacity.html#foreign-impls

[djc]

I wonder how this API relates to ReadBuf. It would be great if there was some safe API that wrapped around the use of ReadBuf to access a Vec's spare capacity, then updated len based on the ReadBufs filled.

[the8472]

FWIW, here is a full-featured API provided by an external crate: https://docs.rs/uninit/0.3.0/uninit/extension_traits/trait.VecCapacity.html#foreign-impls

Maybe we should follow that example and generalize spare_capacity_mut() to return (&mut [T], &mut [MaybeUninit<T>])?

[Shnatsel]

Maybe we should follow that example and generalize spare_capacity_mut() to return (&mut [T], &mut [MaybeUninit<T>])?

#79015 has implemented that, albeit as a private function. Sounds like a good idea to me.

[the8472]

Since #81944 exists now I think vec_spare_capacity is redundant.

[WaffleLapkin]

@the8472

Since #81944 exists now I think vec_spare_capacity is redundant.

That's not actually true due to pointer invalidation, see #81944 (comment) and #82564