Re: What's a "side effect"

From	James Kuyper <jameskuyper@verizon.net>
Newsgroups	comp.std.c++
Subject	Re: What's a "side effect"
Date	2012-10-07 07:43 -0700
Organization	A noiseless patient Spider
Message-ID	<506F093C.1000505@verizon.net> (permalink)
References	<506de288$0$71204$742ec2ed@news.sonic.net>

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On 10/05/2012 04:35 AM, Andy Lutomirski wrote:
>
> I'm trying to userstand the memory model.  [intro.multithread] mentions
> lots of things like:
>
> A release sequence ... is a maximal contiguous sub-sequence of side effects
>
> I know what a /visible/ side effect is (see #13), but that doesn't tell
> me what a side effect is in the first place.  I assume that a "side
> effect" is just a write (e.g. "a = b" has a side effect of modifying a),
> but AFAICS the N3376 has no language to support that assumption.
>
> Am I right?  Should I submit a defect report?

You're right - the expression "a = b" does have a side effect, which is
the modification of the object identified by "a" (unless a very peculiar
operator overload applies). However, there are other kinds of side
effects that don't fit your description:

"Accessing an object designated by a volatile glvalue (3.10), modifying
an object, calling a library I/O function, or calling a function that
does any of those operations are all side effects, ..." (1.9p12) The
phrase "side effects" is italicized in that sentence, which is an ISO
convention for indicating that the sentence containing that phrase
constitutes the definition of that phrase.

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What's a "side effect" Andy Lutomirski <luto@amacapital.net> - 2012-10-05 02:35 -0600
  Re: What's a "side effect" James Kuyper <jameskuyper@verizon.net> - 2012-10-07 07:43 -0700
  Re: What's a "side effect" =3D?ISO-8859-1?Q?Daniel_Kr=3DFCgler?=3D <daniel.kruegler@googlemail.c= om> - 2012-10-08 09:11 -0700

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