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Re: ->=

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On 11/27/2015 08:14 PM, John Bode wrote:
> On Wednesday, November 25, 2015 at 2:40:25 PM UTC-6, James Kuyper wrote:
>> On 11/25/2015 03:24 PM, John Bode wrote:
>>> On Wednesday, November 25, 2015 at 9:12:43 AM UTC-6, Richard Heathfield wrote:
>>>> On 25/11/15 14:53, glen herrmannsfeldt wrote:
>>>>> In a recent post on linked list, there was the common notation:
>>>>>
>>>>>
>>>>>      p = p->next;
>>>>>
>>>>> Though I have written it many times, this time it occured to me
>>>>> that there could have been a C operator ->= such that:
>>>>>
>>>>>     p ->= next;
>> ...
>>
>>> You'd probably want to add a `.=` operator as well. 
>>
>> For consistency with the other compound assignment operators, the expression
>>
>>     s .= member;
>>
>> would have to be equivalent to:
>>
>>     s = s.member
>>
>> That would require that s.member have a type that's compatible with the
>> type of s (6.5.16.1p1). How could that even be possible?
> 
> Derp.
> 
> You're correct, of course.
> 
> Which introduces a bit of an assymetry.  After thinking about it some more,
> I'm not sure it would be that useful an operator.  I mean, `->` is syntactic
> sugar for `(*).`, but it's applicable to all struct member accesses; `->=`
> would only be applicable in a very narrow domain (the member has to have
> the same pointer type as the target).

True - but it's a fairly common narrow domain. Any time you have a
navigate a network of nodes of the same type connected by pointers, this
operator could be convenient, and that's not an uncommon property for C
data structures. Linked lists are just the simplest example of such a
structure.

Note: 6.5.16.2p3 would have to be revised slightly in a way that makes
->= a special case. That clause doesn't explicitly say that E2 is an
expression, but that's clearly what was intended, and is hinted at by
the 'E', and that wouldn't be the case for pstruct->=member. Also,
defining it as equivalent to E1 = E1 op (E2) works for all of the
existing compound assignment operators, but the parenthesis would have
to be removed for ->=. I'm not sure that's sufficient reason to justify
rejecting this idea, but it is a valid thing to object to.

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->= glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-25 14:53 +0000
  Re: ->= Richard Heathfield <rjh@cpax.org.uk> - 2015-11-25 15:12 +0000
    Re: ->= James Kuyper <jameskuyper@verizon.net> - 2015-11-25 11:51 -0500
      Re: ->= "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-25 09:49 -0800
      Re: ->= supercat@casperkitty.com - 2015-11-25 09:55 -0800
    Re: ->= John Bode <jfbode1029@gmail.com> - 2015-11-25 12:24 -0800
      Re: ->= James Kuyper <jameskuyper@verizon.net> - 2015-11-25 15:40 -0500
        Re: ->= John Bode <jfbode1029@gmail.com> - 2015-11-27 17:14 -0800
          Re: ->= James Kuyper <jameskuyper@verizon.net> - 2015-11-27 20:28 -0500
  Re: ->= "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-25 07:35 -0800
  Re: ->= "Charles Richmond" <numerist@aquaporin4.com> - 2015-11-25 15:47 -0600
    Re: ->= James Kuyper <jameskuyper@verizon.net> - 2015-11-25 17:04 -0500
    Re: ->= Nobody <nobody@nowhere.invalid> - 2015-11-26 10:58 +0000
      Re: ->= supercat@casperkitty.com - 2015-11-26 08:55 -0800
  Re: ->= raltbos@xs4all.nl (Richard Bos) - 2015-11-26 00:48 +0000
  Re: ->= Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 14:15 -0800
    Re: ->= supercat@casperkitty.com - 2015-11-27 14:26 -0800
      Re: ->= BartC <bc@freeuk.com> - 2015-11-27 23:38 +0000
        Re: ->= Keith Thompson <kst-u@mib.org> - 2015-11-27 19:37 -0800
          Re: ->= Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-28 06:35 -0800
      Re: ->= Stephen Sprunk <stephen@sprunk.org> - 2015-11-27 17:51 -0600
      Re: ->= Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-28 06:53 -0800
        Re: ->= glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-28 17:12 +0000
          Re: ->= Keith Thompson <kst-u@mib.org> - 2015-11-28 10:26 -0800
            Re: ->= glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-28 19:50 +0000
          Re: ->= BartC <bc@freeuk.com> - 2015-11-28 19:14 +0000
            Re: ->= supercat@casperkitty.com - 2015-11-28 11:48 -0800
              Re: ->= glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-29 22:33 +0000
            Re: ->= glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-28 20:18 +0000
              Re: ->= Stephen Sprunk <stephen@sprunk.org> - 2015-11-28 18:15 -0600
                Re: ->= glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-29 22:44 +0000
                Re: ->= Stephen Sprunk <stephen@sprunk.org> - 2015-11-29 18:25 -0600
                Re: ->= raltbos@xs4all.nl (Richard Bos) - 2015-11-30 10:21 +0000
            Re: ->= Keith Thompson <kst-u@mib.org> - 2015-11-28 13:10 -0800
              Re: ->= BartC <bc@freeuk.com> - 2015-11-28 22:12 +0000
                Re: ->= raltbos@xs4all.nl (Richard Bos) - 2015-11-29 11:42 +0000
                Re: ->= BartC <bc@freeuk.com> - 2015-11-29 14:24 +0000
                Re: "->=" Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-29 10:33 -0500
                Re: "->=" BartC <bc@freeuk.com> - 2015-11-29 17:49 +0000
                Re: ->= supercat@casperkitty.com - 2015-11-29 11:50 -0800
                Re: ->= BartC <bc@freeuk.com> - 2015-11-29 22:37 +0000
                Re: ->= Keith Thompson <kst-u@mib.org> - 2015-11-30 00:23 -0800
              Re: ->= glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-29 23:00 +0000
                Re: ->= Keith Thompson <kst-u@mib.org> - 2015-11-30 00:28 -0800
                Re: ->= Rosario19 <Ros@invalid.invalid> - 2015-12-13 16:29 +0100
  Re: ->= Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-28 14:59 -0500

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