linux-kernel - Re: [PATCH 4/7] rust: sync: introduce `ArcBorrow`

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Date:   Mon, 16 Jan 2023 22:07:36 +0000
From:   Gary Guo <gary@...yguo.net>
To:     Emilio Cobos Álvarez <emilio@...sal.io>
Cc:     Wedson Almeida Filho <wedsonaf@...il.com>,
        rust-for-linux@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] rust: sync: introduce `ArcBorrow`

On Wed, 4 Jan 2023 17:06:50 +0100
Emilio Cobos Álvarez <emilio@...sal.io> wrote:

> Sorry for the drive-by comment, but maybe it saves some work.
> 
> On 1/4/23 16:29, Wedson Almeida Filho wrote:
> > On Sat, 31 Dec 2022 at 19:43, Gary Guo <gary@...yguo.net> wrote:  
> >>
> >> On Wed, 28 Dec 2022 06:03:43 +0000
> >> Wedson Almeida Filho <wedsonaf@...il.com> wrote:
> >>> +pub struct ArcBorrow<'a, T: ?Sized + 'a> {
> >>> +    inner: NonNull<ArcInner<T>>,
> >>> +    _p: PhantomData<&'a ()>,
> >>> +}
> >>> +
> >>> +impl<T: ?Sized> Clone for ArcBorrow<'_, T> {
> >>> +    fn clone(&self) -> Self {
> >>> +        *self
> >>> +    }
> >>> +}
> >>> +
> >>> +impl<T: ?Sized> Copy for ArcBorrow<'_, T> {}  
> >>
> >> Couldn't this just be derived `Clone` and `Copy`?  
> > 
> > Indeed. I'll send a v2 with this.  
> 
> I'm not sure this is true. Deriving will add the T: Copy and T: Clone 
> bound, which I think is not what you want here.
> 
> i.e., I assume you want an ArcBorrow to be Copy even if the underlying T 
> is not.

Thanks for pointing out, I neglected that.

In this case:

Reviewed-by: Gary Guo <gary@...yguo.net>