Re: [PATCH v2] rust: pin-init: add `#[bind]` attribute to access previously initialized fields

[Benno Lossin]

On Wed Sep 10, 2025 at 4:02 PM CEST, Boqun Feng wrote:
> On Wed, Sep 10, 2025 at 02:19:00PM +0200, Benno Lossin wrote:
>> On Wed Sep 10, 2025 at 12:40 PM CEST, Alice Ryhl wrote:
>> > On Wed, Sep 10, 2025 at 12:36 PM Benno Lossin <lossin@xxxxxxxxxx> wrote:
>> >>
>> >> On Wed Sep 10, 2025 at 12:17 PM CEST, Alice Ryhl wrote:
>> >> > On Wed, Sep 10, 2025 at 12:07:53PM +0200, Benno Lossin wrote:
>> >> >> Assigning a field a value in an initializer macro can be marked with the
>> >> >> `#[bind]` attribute. Doing so creates a `let` binding with the same
>> >> >> name. This `let` binding has the type `Pin<&mut T>` if the field is
>> >> >> structurally pinned or `&mut T` otherwise (where `T` is the type of the
>> >> >> field).
>> >> >>
>> >> >> Signed-off-by: Benno Lossin <lossin@xxxxxxxxxx>
>> >> >
>> >> > Is there a reason we can't apply this to all fields and avoid the
>> >> > attribute?
>> >>
>> >> Adding the attribute was due to Boqun's concern on v1 [1]. I think it
>> >> might be surprising too, but I'm also happy with no attribute.
>> >>
>> >> [1]: https://lore.kernel.org/all/aLshd0_C-1rh3FAg@tardis-2.local
>> >
>> > IMO the ideal is if it works without an attribute. Perhaps trying that
>> > in the kernel is a reasonable experiment to find out whether that's
>> > reasonable to do for the general language feature?
>> 
>> @Boqun what is your opinion on this?
>> 
>
> If we plan to make the in-place initializer language feature behave
> similar, as I asked here [1], then dropping `#[bind]` seems good to me.

I don't think we can promise how that language feature is going to look
like. It will definitely support accessing already initialized fields,
but in what form remains to be seen.

---
Cheers,
Benno

> [1]: https://lore.kernel.org/rust-for-linux/aLshd0_C-1rh3FAg@tardis-2.local/
>
> Thanks!
>
> Regards,
> Boqun
>
>> I'm open to take v2 or v1, whatever you guys prefer.
>> 
>> ---
>> Cheers,
>> Benno