linux-kernel - Re: [PATCH v6 2/6] rust: str: implement `Index` for `BStr`

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Message-ID: <20250211164004.6de768c3@eugeo>
Date: Tue, 11 Feb 2025 16:40:04 +0000
From: Gary Guo <gary@...yguo.net>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, Alice
 Ryhl <aliceryhl@...gle.com>, Masahiro Yamada <masahiroy@...nel.org>, Nathan
 Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, Luis
 Chamberlain <mcgrof@...nel.org>, Trevor Gross <tmgross@...ch.edu>, Adam
 Bratschi-Kaye <ark.email@...il.com>, rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, Petr Pavlu
 <petr.pavlu@...e.com>, Sami Tolvanen <samitolvanen@...gle.com>, Daniel
 Gomez <da.gomez@...sung.com>, Simona Vetter <simona.vetter@...ll.ch>, Greg
 KH <gregkh@...uxfoundation.org>, linux-modules@...r.kernel.org
Subject: Re: [PATCH v6 2/6] rust: str: implement `Index` for `BStr`

On Tue, 11 Feb 2025 16:57:36 +0100
Andreas Hindborg <a.hindborg@...nel.org> wrote:

> The `Index` implementation on `BStr` was lost when we switched `BStr` from
> a type alias of `[u8]` to a newtype. This patch adds back `Index` by
> implementing `Index` for `BStr` when `Index` would be implemented for
> `[u8]`.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
>  rust/kernel/str.rs | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index 002dcddf7c768..1eb945bed77d6 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -114,6 +114,17 @@ fn eq(&self, other: &Self) -> bool {
>      }
>  }
>  
> +impl<Idx> Index<Idx> for BStr
> +where
> +    Idx: core::slice::SliceIndex<[u8], Output = [u8]>,

I think I'd prefer

	[T]: Index<Idx>,

here.

> +{
> +    type Output = Self;
> +
> +    fn index(&self, index: Idx) -> &Self::Output {
> +        BStr::from_bytes(&self.0[index])
> +    }
> +}
> +
>  /// Creates a new [`BStr`] from a string literal.
>  ///
>  /// `b_str!` converts the supplied string literal to byte string, so non-ASCII
>