Re: [PATCH] rust: pin-init: add references to previously initialized fields

["Benno Lossin" <lossin@kernel.org>]

On Mon Sep 8, 2025 at 9:38 PM CEST, Boqun Feng wrote:
> On Mon, Sep 08, 2025 at 10:57:36AM +0200, Danilo Krummrich wrote:
>> On Mon Sep 8, 2025 at 10:27 AM CEST, Benno Lossin wrote:
>> > On Mon Sep 8, 2025 at 4:08 AM CEST, Boqun Feng wrote:
>> >> On Mon, Sep 08, 2025 at 01:33:26AM +0200, Danilo Krummrich wrote:
>> >>> On Mon Sep 8, 2025 at 12:51 AM CEST, Benno Lossin wrote:
>> >>> > I actually came up with a third option that looks best IMO:
>> >>> >
>> >>> >     init!(MyStruct {
>> >>> >         x: 42,
>> >>> >         #[with_binding]
>> >>> >         y: 24,
>> >>> >         z: *y,
>> >>> >     })
>> >>> >
>> >>> > The `#[with_binding]` attribute makes the macro generate a variable `y`.
>> >>> > `x` & `z` don't give access to their value. (we of course should come up
>> >>> > with a better name).
>> >>> >
>> >>> > Any thoughts?
>> >>> 
>> >>> It may be a bit verbose is some cases, but it makes things pretty obvious, so
>> >>> LGTM.
>> >>> 
>> >>> How about just #[bind] or #[access]?
>> >
>> > I like `#[bind]`.
>> >
>> >> #[shadow] or #[maybe_rebind] ? Or #[pin_ref], the last one is clear
>> >> about the purpose.
>> >
>> > Hmm in `init!` it's never pinned.
>> 
>> I thought about #[shadow] as well, but it is not really accurate I think, as we
>> might not shadow anything. #[maybe_rebind] sounds a bit like it conditionally
>> rebinds, as in "it may not do anything", but it always binds.
>> 
>> So, I think it should one clear instruction, i.e. #[bind], #[access], #[ref],
>> #[use], #[let], etc.
>
> In that sense I think `#[let]` is best? Because it indicates this field
> initialization works as a `let`-statement (in term of creating a new
> binding), of course I don't have strong ojections against other options.

Ultimately I decided to go with `#[bind]`, since I felt like `#[let]`
might be confused with just having a let statement (ie replacing the
assignment with a let binding).

`#[bind]` also might be confused with some device binding I guess, but
we can rename it's too bad.

---
Cheers,
Benno