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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Fri, 16 Apr 2021 23:19:18 +0200
Message-ID: <CANiq72=3zZvdEsp-AH2Xj1nuvfGOQQ1WGmav6i4nFTz-3-_c_w@mail.gmail.com>
Subject: Re: [PATCH 04/13] Kbuild: Rust support
To:     Willy Tarreau <w@1wt.eu>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Miguel Ojeda <ojeda@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        rust-for-linux@vger.kernel.org,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Geoffrey Thomas <geofft@ldpreload.com>,
        Finn Behrens <me@kloenk.de>,
        Adam Bratschi-Kaye <ark.email@gmail.com>,
        Wedson Almeida Filho <wedsonaf@google.com>,
        Michael Ellerman <mpe@ellerman.id.au>
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On Fri, Apr 16, 2021 at 10:22 PM Willy Tarreau <w@1wt.eu> wrote:
>
> So it simply does the equivalent of:
>
>   struct result {
>      int status;
>      int error;
>   };

Not exactly, it is more like a tagged union, as Connor mentioned.

However, and this is the critical bit: it is a compile-time error to
access the inactive variants (in safe code). In C, it is on you to
keep track which one is the current one.

>      kill_foo();   // only for rust, C doesn't need it

Please note that `kill_foo()` is not needed in Rust -- it was an
example of possible cleanup (since Al mentioned resources/cleanup)
using RAII.

Cheers,
Miguel