From: "René Scharfe" <l.s.r@web.de>
To: Brandon Williams <bmwill@google.com>
Cc: Johannes Schindelin <Johannes.Schindelin@gmx.de>,
Johannes Sixt <j6t@kdbg.org>, Git List <git@vger.kernel.org>,
Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 1/5] add SWAP macro
Date: Tue, 31 Jan 2017 22:03:01 +0100 [thread overview]
Message-ID: <8e94756a-c3a5-9b81-268d-d0f36876f710@web.de> (raw)
In-Reply-To: <20170130222157.GC35626@google.com>
Am 30.01.2017 um 23:21 schrieb Brandon Williams:
> On 01/30, René Scharfe wrote:
>> Am 30.01.2017 um 22:03 schrieb Johannes Schindelin:
>>> It is curious, though, that an
>>> expression like "sizeof(a++)" would not be rejected.
>>
>> Clang normally warns about something like this ("warning: expression
>> with side effects has no effect in an unevaluated context
>> [-Wunevaluated-expression]"), but not if the code is part of a
>> macro. I don't know if that's intended, but it sure is helpful in
>> the case of SWAP.
>>
>>> Further, what would SWAP(a++, b) do? Swap a and b, and *then* increment a?
>>
>> That might be a valid expectation, but GCC says "error: lvalue
>> required as unary '&' operand" and clang puts it "error: cannot take
>> the address of an rvalue of type".
>>
>> René
>
> Perhaps we could disallow a side-effect operator in the macro. By
> disallow I mean place a comment at the definition to the macro and
> hopefully catch something like that in code-review. We have the same
> issue with the `ALLOC_GROW()` macro.
SWAP(a++, ...) is caught by the compiler, SWAP(*a++, ...) works fine.
Technically that should be enough. :) A comment wouldn't hurt, of course.
René
next prev parent reply other threads:[~2017-01-31 21:03 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-28 21:13 [PATCH 0/5] introduce SWAP macro René Scharfe
2017-01-28 21:38 ` [PATCH 1/5] add " René Scharfe
2017-01-30 15:39 ` Johannes Schindelin
2017-01-30 16:48 ` René Scharfe
2017-01-30 20:48 ` Johannes Schindelin
2017-01-30 21:46 ` René Scharfe
2017-01-31 12:13 ` Johannes Schindelin
2017-01-31 21:02 ` René Scharfe
2017-02-01 0:44 ` Ramsay Jones
2017-02-01 11:39 ` Johannes Schindelin
2017-01-30 16:01 ` Johannes Schindelin
2017-01-30 16:59 ` René Scharfe
2017-01-30 18:41 ` Johannes Sixt
2017-01-30 21:03 ` Johannes Schindelin
2017-01-30 22:09 ` René Scharfe
2017-01-30 22:21 ` Brandon Williams
2017-01-31 21:03 ` René Scharfe [this message]
2017-01-31 21:35 ` Jeff King
2017-01-31 22:29 ` Junio C Hamano
2017-01-31 22:36 ` Jeff King
2017-02-01 11:28 ` Johannes Schindelin
2017-02-01 11:47 ` Jeff King
2017-02-01 18:06 ` René Scharfe
2017-02-01 18:33 ` Junio C Hamano
2017-02-07 22:04 ` René Scharfe
2017-02-07 22:30 ` Junio C Hamano
2017-02-08 15:14 ` Johannes Schindelin
2017-01-31 12:03 ` Johannes Schindelin
2017-04-24 11:29 ` Jeff King
2017-04-24 11:49 ` Jeff King
2017-04-24 13:13 ` Duy Nguyen
2017-04-28 17:04 ` René Scharfe
2017-04-28 21:49 ` Jeff King
2017-04-29 18:16 ` René Scharfe
2017-04-30 3:11 ` Jeff King
2017-05-02 5:29 ` René Scharfe
2017-01-28 21:40 ` [PATCH 2/5] apply: use " René Scharfe
2017-01-28 21:40 ` [PATCH 3/5] " René Scharfe
2017-01-30 16:03 ` Johannes Schindelin
2017-01-30 17:18 ` René Scharfe
2017-01-30 22:22 ` Junio C Hamano
2017-01-31 21:02 ` René Scharfe
2017-01-28 21:41 ` [PATCH 4/5] diff: " René Scharfe
2017-01-30 16:04 ` Johannes Schindelin
2017-01-30 17:26 ` René Scharfe
2017-01-30 22:22 ` Junio C Hamano
2017-01-28 21:42 ` [PATCH 5/5] graph: " René Scharfe
2017-01-30 16:16 ` Johannes Schindelin
2017-01-30 17:41 ` René Scharfe
2017-01-30 23:20 ` [PATCH 0/5] introduce " Junio C Hamano
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