linux-kernel - Re: [PATCH v6 2/2] rust: list: make the cursor point between elements

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Message-ID: <CAH5fLgi3bXB3=rjkP=pHEuzsdOuLHPcNQW-+Krc8vj56KJSUDw@mail.gmail.com>
Date: Fri, 31 Jan 2025 21:44:43 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: 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>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/2] rust: list: make the cursor point between elements

On Fri, Jan 31, 2025 at 9:16 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> 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]
> Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
> Reviewed-by: Boqun Feng <boqun.feng@...il.com>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>

> +    /// Insert an element at this cursor's location.
> +    pub fn insert(self, item: ListArc<T, ID>) {

Oops this needs to be `mut self` to compile. Those last minute changes get ya.

Alice