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Re: lvalues from the ternary op

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supercat@casperkitty.com writes:

> On Friday, February 24, 2017 at 9:58:56 AM UTC-6, Tim Rentsch wrote:
>> The problem you're having now is that your conclusions are not
>> consistent with everyone else's.  Until you learn to express
>> yourself in a way that communicates effectively with other
>> people, /and vice versa/, that problem is not going to go away.
>> A tall order, I know, but there it is.
>
> The following questions assume the following declaration is in scope, and
> for questions about code, assume the scope is within some function and is
> executed.
>
>     union { unsigned u; float f; } uf;
>
> True or false:  the Standard specifies as a runtime constraint that stored
> value of an object of type "float" may not be accessed with an lvalue of
> type "unsigned".  Because this is a runtime constraint, the Standard
> allow implementations to do anything whatsoever if code violates it.  Such
> permission overrides anything else in the Standard that would otherwise
> define the behavior of the code.
>
> True or false:  the Standard specifies that the above declaration will, among
> other things, create an object of type "float" which is stored within "uf",
> and such object will exist as long as containing "uf" object exists.
>
> True or false:  the Standard specifies that the expression "uf.u" will
> is an lvalue of type "unsigned".
>
> True or false:  the Standard allows an implementation to process the
> statement "uf.u = 4;" in a way that writes to the stored value of the float
> value stored within "uf".
>
> True or false:  the Standard allows an implementation to process the
> statement "uf.u = 4;" in a way that would cause a stored value of type
> "float" to be accessed using an lvalue of type "unsigned", violating a
> runtime constraint.
>
> True or false:  if any of the ways in which a conforming implementation
> could process an action invoke UB, the action itself invokes UB.
>
> If all of the above are true, they would imply that given the above union,
> an attempt to write member "uf.u" may be regarded as violating a runtime
> constraint, and would thus invoke UB, regardless of whether code makes any
> effort to use "uf.f".
>
> The only way I can see for the Standard to impose any requirements on the
> behavior of code which writes "uf.u" would be for the language of the
> Standard to be interpreted in such a way that at least one of the above
> true-false statements is false.  I suspect that that any compiler that
> applied aliasing constraints to the above code for the purpose of
> disregarding everything else would be widely denounced as a piece of junk.
> Since the Standard acknowledges the possibility of conforming-but-useless
> implementations, however, I see no reason to believe it a compiler that
> interpreted aliasing rules as described could not be conforming.

You're making the same mistake as before.  Your comments are
phrased in the style of making an argument for your point of
view.  What you need to do instead is state your views explicitly
as being your opinion, eg, "I believe the Standard says an object
of union type contains one or more overlapping objects, one for
each member".  Then, _after_ giving those views, ask about what
other people think and invite them to react or give their own
views or both.  Maybe the most important point is to try to
listen rather than argue.

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Re: lvalues from the ternary op Manfred <noname@invalid.add> - 2017-01-04 19:46 +0100
  Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-04 11:08 -0800
  Re: lvalues from the ternary op Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-04 21:10 +0000
    Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 13:48 -0800
      Re: lvalues from the ternary op Ian Collins <ian-news@hotmail.com> - 2017-01-05 11:07 +1300
        Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 14:20 -0800
      Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-04 14:41 -0800
        Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 15:21 -0800
          Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-04 15:52 -0800
            Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 16:37 -0800
            Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 18:31 -0800
              Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-13 17:26 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-13 17:49 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-15 22:53 -0800
    Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-13 17:08 -0800
      Re: lvalues from the ternary op Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-14 02:15 +0000
        Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-15 22:51 -0800
      Re: lvalues from the ternary op luser droog <luser.droog@gmail.com> - 2017-01-16 23:09 -0800
        Re: lvalues from the ternary op Manfred <noname@invalid.add> - 2017-01-18 14:51 +0100
          Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-18 09:59 -0800
            Re: lvalues from the ternary op Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2017-01-18 13:12 -0500
            Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-18 12:11 -0800
              Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-18 12:45 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-18 14:07 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-18 14:40 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-18 16:10 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-18 18:08 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-19 06:44 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-19 08:40 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-19 12:32 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-20 06:01 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-20 08:15 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-20 10:51 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-20 11:32 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-20 13:41 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-23 07:04 -0800
                Re: lvalues from the ternary op Ike Naar <ike@iceland.freeshell.org> - 2017-01-23 17:59 +0000
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-23 10:57 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-31 08:45 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-31 09:13 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-31 10:17 -0800
                Re: lvalues from the ternary op Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-01 01:51 +0000
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-01 14:24 -0800
                Re: lvalues from the ternary op Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-02 03:07 +0000
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 04:43 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-04 08:01 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-09 09:06 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-09 11:56 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-12 10:29 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-12 13:43 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-19 21:44 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-20 08:15 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-24 07:58 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-24 10:00 -0800
                Re: lvalues from the ternary op scott@slp53.sl.home (Scott Lurndal) - 2017-02-24 18:58 +0000
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-24 13:03 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-02-24 14:11 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-02-24 12:42 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-02-24 13:49 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-24 13:58 -0800
                Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-02-24 14:56 -0800
                Re: lvalues from the ternary op supercat <flatfinger@casperkitty.com> - 2017-02-25 14:00 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-25 09:23 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-25 09:43 -0800
                Re: lvalues from the ternary op Kelsey Bjarnason <kbjarnason@gmail.com> - 2017-02-01 22:47 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-02 10:12 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 07:51 -0800
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-04 08:18 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-09 08:58 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 04:00 -0800
                Re: lvalues from the ternary op Kelsey Bjarnason <kbjarnason@gmail.com> - 2017-02-04 09:35 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 09:35 -0800
                Re: lvalues from the ternary op Robert Wessel <robertwessel2@yahoo.com> - 2017-01-31 13:36 -0600
                Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-31 12:23 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-01 13:48 -0800
                Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-31 08:53 -0800
            Re: lvalues from the ternary op Manfred <noname@invalid.add> - 2017-01-19 14:10 +0100
        Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-30 12:05 -0800

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