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From: Andreas Hindborg <a.hindborg@kernel.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: Miguel Ojeda <ojeda@kernel.org>, Boqun Feng <boqun.feng@gmail.com>, Gary
 Guo <gary@garyguo.net>, =?utf-8?Q?Bj=C3=B6rn?= Roy Baron
 <bjorn3_gh@protonmail.com>, Benno
 Lossin <lossin@kernel.org>, Alice Ryhl <aliceryhl@google.com>, Trevor
 Gross <tmgross@umich.edu>, Danilo Krummrich <dakr@kernel.org>,
 rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] rust: impl_flags: add conversion functions
In-Reply-To: <CANiq72kLDR5m8iVjDYT7doCw-z7oj2ijVK3QuA9ees7jL7zW0w@mail.gmail.com>
References: <20260215-impl-flags-additions-v1-0-6538c8fb841c@kernel.org>
 <20260215-impl-flags-additions-v1-1-6538c8fb841c@kernel.org>
 <CANiq72kLDR5m8iVjDYT7doCw-z7oj2ijVK3QuA9ees7jL7zW0w@mail.gmail.com>
Date: Tue, 12 May 2026 10:05:30 +0200
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Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> writes:

> On Sun, Feb 15, 2026 at 9:23=E2=80=AFPM Andreas Hindborg <a.hindborg@kern=
el.org> wrote:
>>
>> +        impl ::core::convert::From<$flag> for $ty {
>> +            #[inline]
>> +            fn from(value: $flag) -> Self {
>> +                // SAFETY: All `$flag` values are valid for use as `$ty=
`.
>> +                unsafe { core::mem::transmute::<$flag, $ty>(value) }
>> +            }
>> +        }
>
> Why do we need the transmute instead of a cast? Did you notice a differen=
ce?

No, I did not think of using `as`. I can do that.

> Same in the other one -- why not constructing the object normally?

Will do.

> Also, you can use `Self` for `$ty` and `$flags` to make it easier to read.

Ok.

>
> In addition, I would suggest an early return with a simple `if`.

Ok.

>
> Finally, it wouldn't hurt adding a one-liner example for each at the top.

I'll add an example.


Best regards,
Andreas Hindborg