linux-kernel - Re: [PATCH] rust: kernel: drop repetition in offset

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Date:   Fri, 16 Dec 2022 23:30:34 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Wedson Almeida Filho <wedsonaf@...il.com>,
        Wei Liu <wei.liu@...nel.org>, rust-for-linux@...r.kernel.org,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>
Subject: Re: [PATCH] rust: kernel: drop repetition in offset_of macro

On Fri, Dec 16, 2022 at 02:15:16PM -0800, Boqun Feng wrote:
> On Fri, Dec 16, 2022 at 06:26:57PM +0000, Wedson Almeida Filho wrote:
> > On Fri, 16 Dec 2022 at 17:49, Wei Liu <wei.liu@...nel.org> wrote:
> > >
> > > It doesn't make sense to allow multiple fields to be specified in
> > > offset_of.
> > 
> > Why do you say it doesn't make sense?
> > 
> > Here's what I had in mind:
> > ```
> >     struct Y {
> >         z: u32
> >     }
> >     struct X {
> >         y: Y
> >     }
> >     offset_of!(X, y.z)
> 
> For me, it's not very obvious that "y.z" is multiples of token trees
> rather a single token tree ;-)
> 
> Maybe some examples of the match pattern of macros can help people catch
> up faster? Like
> 
> 	"y.z" => tt [y], tt [.], tt [z]
> 
> I will defer to Gary or Bjorn for a better quick guide of Rust macros
> ;-)
> 

What will be  even better is someone please contribute such a macro to
libcore so that I don't have to replicate the code snippet everywhere.
:-)

I have a version somewhere, the second argument matches against ident,
which was definitely not as flexible as tt.

Thanks,
Wei.