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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: ->=
Date: Fri, 27 Nov 2015 19:37:28 -0800
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BartC <bc@freeuk.com> writes:
[...]
>> On Friday, November 27, 2015 at 4:15:37 PM UTC-6, Tim Rentsch wrote:
[...]
>  >> best it's no more than syntactic saccharin.  Note also it
>  >> requires revising the rule stated in the first sentence of
>  >> 6.5.16.2 p3.  Kind of sticks out like a sort thumb.
>
> I didn't understand that bit. But I can see that if a member name 
> normally only follows a "." or "->" token, now it will need to be 
> allowed after "->=" too. It can't just be mapped to = and ->, unless the 
> implementation ensures that any side-effects occur just once.

6.5.16.2p3 says:

    A compound assignment of the form E1 op = E2 is equivalent to
    the simple assignment expression E1 = E1 op (E2), except that
    the lvalue E1 is evaluated only once, and with respect to an
    indeterminately-sequenced function call, the operation of a
    compound assignment is a single evaluation.

The semantics of the `->=` operator would have to be defined
without the parentheses, since `foo->(bar)` is illegal even when
`foo->bar` is legal.  Not a fatal problem, but it would be one more
special case.

(Tim: I suggest that you'd save a some people some time if you'd quote
the sentence rather than just citing the section and paragraph number.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"