From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Jeff King <peff@peff.net>
Cc: "René Scharfe" <l.s.r@web.de>,
"Brandon Williams" <bmwill@google.com>,
"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: Wed, 1 Feb 2017 12:28:13 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.20.1702011225250.3469@virtualbox> (raw)
In-Reply-To: <20170131213507.uiwmkkcg7umvd3f4@sigill.intra.peff.net>
[-- Attachment #1: Type: text/plain, Size: 1390 bytes --]
Hi Peff,
On Tue, 31 Jan 2017, Jeff King wrote:
> On Tue, Jan 31, 2017 at 10:03:01PM +0100, René Scharfe wrote:
>
> > > 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.
>
> One funny thing is that your macro takes address-of itself, behind the
> scenes. I wonder if it would be more natural for it to take
> pointers-to-objects, making it look more like a real function (i.e.,
> SWAP(&a, &b) instead of SWAP(a, b)". And then these funny corner cases
> become quite obvious in the caller, because the caller is the one who
> has to type "&".
But forcing SWAP(&a, &b) would make it even more cumbersome to use, and it
would also make it harder to optimize, say, by using registers instead of
addressable memory (think swapping two 32-bit integers: there is *no* need
to write them into memory just to swap them).
And I think I should repeat my point that this discussion veers towards
making simple swaps *more* complicated, rather than less complicated. Bad
direction.
Ciao,
Dscho
next prev parent reply other threads:[~2017-02-01 11:28 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
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 [this message]
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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