linux-kernel - Re: [PATCH v4 4/7] rust: num: add `into

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Message-Id: <DG1CQZ54QY3K.28BHAW8Q3Q4A4@garyguo.net>
Date: Thu, 29 Jan 2026 20:23:32 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Alexandre Courbot" <acourbot@...dia.com>, "Gary Guo" <gary@...yguo.net>
Cc: "Danilo Krummrich" <dakr@...nel.org>, "Alice Ryhl"
 <aliceryhl@...gle.com>, "Daniel Almeida" <daniel.almeida@...labora.com>,
 "Miguel Ojeda" <ojeda@...nel.org>, "Boqun Feng" <boqun.feng@...il.com>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Trevor
 Gross" <tmgross@...ch.edu>, "Yury Norov" <yury.norov@...il.com>, "John
 Hubbard" <jhubbard@...dia.com>, "Alistair Popple" <apopple@...dia.com>,
 "Joel Fernandes" <joelagnelf@...dia.com>, "Timur Tabi" <ttabi@...dia.com>,
 "Edwin Peer" <epeer@...dia.com>, "Eliot Courtney" <ecourtney@...dia.com>,
 "Dirk Behme" <dirk.behme@...bosch.com>, "Steven Price"
 <steven.price@....com>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 4/7] rust: num: add `into_inner` method to `Bounded`

On Thu Jan 29, 2026 at 8:05 AM GMT, Alexandre Courbot wrote:
> On Thu Jan 29, 2026 at 12:43 AM JST, Gary Guo wrote:
>> On Wed Jan 28, 2026 at 2:37 AM GMT, Alexandre Courbot wrote:
>>> This is useful to access the inner value in const contexts.
>>>
>>> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
>>> ---
>>>  rust/kernel/num/bounded.rs | 16 ++++++++++++++++
>>>  1 file changed, 16 insertions(+)
>>>
>>> diff --git a/rust/kernel/num/bounded.rs b/rust/kernel/num/bounded.rs
>>> index b41ca6df1525..850827033f67 100644
>>> --- a/rust/kernel/num/bounded.rs
>>> +++ b/rust/kernel/num/bounded.rs
>>> @@ -388,6 +388,22 @@ pub fn get(self) -> T {
>>>          *self.deref()
>>>      }
>>>  
>>> +    /// Returns the wrapped value as the backing type.
>>> +    ///
>>> +    /// This is a const-friendly variant of [`Self::get`] that can be used in const contexts.
>>> +    ///
>>> +    /// # Examples
>>> +    ///
>>> +    /// ```
>>> +    /// use kernel::num::Bounded;
>>> +    ///
>>> +    /// const V: u32 = Bounded::<u32, 4>::new::<7>().into_inner();
>>> +    /// assert_eq!(V, 7u32);
>>> +    /// ```
>>> +    pub const fn into_inner(self) -> T {
>>> +        self.0
>>> +    }
>>
>> This is... just `get`.
>>
>> You can implement it (with the `fits_with_in` check) in the same manner as the
>> const new.
>
> But unfortunately doing so also prevents `get` from being called from
> generic code, which is a must-have. Or am I misunderstanding your
> suggestion?

Can you remove the `fits_with_in` check then and just provide `self.0` in `get`
then?

If the assume is really important, then we should at least name this `get_const`
(or `const_get`) to indicate that this is a limitation caused by const eval, not
a completely different method as the name would otherwise suggest.

Best,
Gary