linux-kernel - Re: [PATCH v2 2/2] rust: list: make the cursor point between elements

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Message-ID: <87h65sb9k7.fsf@kernel.org>
Date: Tue, 21 Jan 2025 14:06:32 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Miguel Ojeda" <ojeda@...nel.org>,  "Alex Gaynor"
 <alex.gaynor@...il.com>,  "Boqun Feng" <boqun.feng@...il.com>,  "Gary Guo"
 <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,  "Benno
 Lossin" <benno.lossin@...ton.me>,  "Trevor Gross" <tmgross@...ch.edu>,
  <rust-for-linux@...r.kernel.org>,  <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] rust: list: make the cursor point between elements

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> I've been using the linked list cursor for a few different things, and I
> find it inconvenient to use because all of the functions have signatures
> along the lines of `Self -> Option<Self>`. The root cause of these
> signatures is that the cursor points *at* an element, rather than
> *between* two elements.
>
> Thus, change the cursor API to point between two elements. This is
> inspired by the stdlib linked list (well, really by this guy [1]), which
> also uses cursors that point between elements.
>
> The `peek_next` method returns a helper that lets you look at and
> optionally remove the element, as one common use-case of cursors is to
> iterate a list to look for an element, then remove that element.
>
> For many of the methods, this will reduce how many we need since they
> now just need a prev/next method, instead of the current state where you
> may end up needing all of curr/prev/next. Also, if we decide to add a
> function for splitting a list into two lists at the cursor, then a
> cursor that points between elements is exactly what makes the most
> sense.
>
> Another advantage is that this means you can now have a cursor into an
> empty list.
>
> Link: https://rust-unofficial.github.io/too-many-lists/sixth-cursors-intro.html [1]
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>

Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>

If you for some reason find yourself sending a new version, it would be
cool if the example actually executed the functions and made some
asserts.

Best regards,
Andreas Hindborg