Re: [PATCH v10 1/2] rust: types: add `ForeignOwnable::PointedTo`

[Tamir Duberstein]

On Mon, Nov 25, 2024 at 9:49 AM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
>
> On Wed, Nov 20, 2024 at 12:48 PM Tamir Duberstein <tamird@xxxxxxxxx> wrote:
> >
> > Allow implementors to specify the foreign pointer type; this exposes
> > information about the pointed-to type such as its alignment.
> >
> > This requires the trait to be `unsafe` since it is now possible for
> > implementors to break soundness by returning a misaligned pointer.
> >
> > Encoding the pointer type in the trait (and avoiding pointer casts)
> > allows the compiler to check that implementors return the correct
> > pointer type. This is preferable to directly encoding the alignment in
> > the trait using a constant as the compiler would be unable to check it.
> >
> > Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx>
>
> I'm not super convinced by this way forward. It introduces more casts
> to/from c_void in code using it, and forces us to expose internal
> types such as ArcInner. Does anyone else have thoughts on this?

It's certainly a trade-off. The alternative (something like exposing
`const ALIGNMENT: usize`) would nullify the compiler's ability to
check implementations.