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

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Message-ID: <aL8wnJcro6uXiD74@tardis-2.local>
Date: Mon, 8 Sep 2025 12:38:04 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Benno Lossin <lossin@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Fiona Behrens <me@...enk.dev>, Alban Kurti <kurti@...icto.ai>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Wilczy´nski <kwilczynski@...nel.org>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: pin-init: add references to previously initialized
 fields

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.

Regards,
Boqun