linux-kernel - Re: [PATCH 1/4] rust: alloc: implement `Borrow` and `BorrowMut` for `Vec`

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Message-Id: <DAL8LBJYGJU8.H23CBQ07RAMI@kernel.org>
Date: Fri, 13 Jun 2025 09:45:33 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Alexandre Courbot" <acourbot@...dia.com>, "Danilo Krummrich"
 <dakr@...nel.org>, "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>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] rust: alloc: implement `Borrow` and `BorrowMut` for
 `Vec`

On Fri Jun 13, 2025 at 7:35 AM CEST, Alexandre Courbot wrote:
> On Wed Jun 4, 2025 at 4:34 PM JST, Benno Lossin wrote:
>> On Mon Jun 2, 2025 at 3:13 AM CEST, Alexandre Courbot wrote:
>>> Hi Benno,
>>>
>>> On Mon Jun 2, 2025 at 1:11 AM JST, Benno Lossin wrote:
>>>> On Sun Jun 1, 2025 at 5:00 AM CEST, Alexandre Courbot wrote:
>>>>> Implement these two common traits, which allow generic types to store
>>>>> either an owned value or a reference to it.
>>>>
>>>> I don't understand the second part of the sentence.
>>>
>>> I want to say that Borrow allows you to do something like:
>>>
>>>     struct Foo<B: Borrow<u32>>(B);
>>>
>>>     // `foo1` owns its value...
>>>     let foo1 = Foo(0x12);
>>>
>>>     let i = 0x24;
>>>     // ... but `foo2` just borrows it, subject to the lifetime of `i`.
>>>     let foo2 = Foo(&i);
>>>
>>> And the implementations in this series also let you do:
>>>
>>>     // `foo3`'s value is owned, but heap-allocated
>>>     let foo3 = Arc::new(KBox::new(0x56, GFP_KERNEL)?);
>>>
>>>     let j = Arc::new(0x78, GFP_KERNEL)?;
>>>     // `foo4`'s value is shared and its lifetime runtime-managed.
>>>     let foo4 = Foo(j.clone());
>>
>> How about something like:
>>
>>     Implement `Borrow<[T]>` and `BorrowMut<[T]>` for `Vec<T>`. This allows
>>     `Vec<T>` to be used in generic APIs asking for types implementing those
>>     traits. `[T; N]` and `&mut [T]` also implement those traits allowing
>>     users to use either owned, borrowed and heap-owned values.
>
> This is super clear, and I think I'll just reuse this message as-is if
> that's ok with you. Thanks!

Sure!

---
Cheers,
Benno