Re: Why does this work on Xcode ???

From	James Kuyper <jameskuyper@alumni.caltech.edu>
Newsgroups	comp.lang.c++
Subject	Re: Why does this work on Xcode ???
Date	2019-08-26 00:43 -0400
Organization	A noiseless patient Spider
Message-ID	<qjvo23$2rb$1@dont-email.me> (permalink)
References	(12 earlier) <qjoplk$ep$1@dont-email.me> <qjotnh$p13$1@dont-email.me> <qjpki9$vhs$1@dont-email.me> <qjtkrh$gd1$1@dont-email.me> <qjtrb2$hvu$2@dont-email.me>

Show all headers | View raw

On 8/25/19 7:27 AM, Alf P. Steinbach wrote:
> On 25.08.2019 11:36, David Brown wrote:
>> On 23/08/2019 23:07, Alf P. Steinbach wrote:
>>> On 23.08.2019 16:37, David Brown wrote:
>>> [snip]
>>>>   It would be an
>>>> unpopular tool, but this would not affect the observable behaviour and
>>>> thus it would not affect the conformance of the compiler.
>>>
>>> It would affect observable behavior. One would get wrong results or
>>> crashes. Instead of with a conforming compiler, correct results.
>>
>> No.  Please re-read the part of the C++ standard explaining what
>> "observable behaviour" is in regards to the standards.  It does /not/
>> mean "behaviour observed by the user".
> 
> In your opinion results are not part of observable behavior.

No, certain kinds of results do qualify as observable behavior. The
problem is not the observable behavior, except insofar as stack usages
does NOT qualify as such. The problem is resource limits, and on systems
which use them, stack is definitely a resource with a finite limit.

Because an implementation is excused from executing programs correctly
when resource limits are exceeded, the requirement that observable
behavior must occur as specified by the standard applies only when
enough resources are available to execute the program. The standard
imposes no requirements on the minimum amount of resources that must be
available, nor on the maximum amount that may be required. In fact, the
standard says nothing at all about the particular resource (stack space)
that is relevant to this thread.

Therefore, the fact that a recursive implementation of a piece of code
may require more resources than an iterative one does not render
translation of iterative code into a recursive implementation
non-conforming. So long as both ways of implementing the code produce
the required observable behavior when sufficient resources are
available, it doesn't matter, as far as standard conformance is
concerned, that the amount of resources required to produce that
behavior is radically different for the two algorithms. That's purely an
issue of QoI, outside the scope of the C++ standard.

It was never intended to be the case that knowing that an implementation
of C++ is fully conforming would be sufficient to ensure that the
implementation is useful for any particular purpose (or indeed, for any
purpose whatsoever). Too many things that are relevant to usefulness are
outside the scope of the C++ standard, starting with the execution time
of C++ code, which is completely unspecified. If you consider the C++
standard to be impractical, that's because it was never intended to be
practical in that sense. You need to also evaluate the Quality of
Implementation (QoI) of a fully conforming implementation before you can
determine whether it's actually useful for anything.

Thread

Why does this work on Xcode ??? Bob Langelaan <bobl0456@gmail.com> - 2019-07-16 22:03 -0700
  Re: Why does this work on Xcode ??? Paavo Helde <myfirstname@osa.pri.ee> - 2019-07-17 08:46 +0300
  Re: Why does this work on Xcode ??? Öö Tiib <ootiib@hot.ee> - 2019-07-17 00:06 -0700
    Re: Why does this work on Xcode ??? Öö Tiib <ootiib@hot.ee> - 2019-07-17 01:44 -0700
  Re: Why does this work on Xcode ??? Juha Nieminen <nospam@thanks.invalid> - 2019-07-17 07:46 +0000
  Re: Why does this work on Xcode ??? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-07-17 09:12 -0400
  Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-07-17 17:01 +0200
    Re: Why does this work on Xcode ??? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2019-07-17 22:15 +0100
      Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-07-17 23:29 +0200
        Re: Why does this work on Xcode ??? Christian Gollwitzer <auriocus@gmx.de> - 2019-07-19 08:27 +0200
          Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-07-19 09:09 +0200
            Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-07-19 09:24 +0200
            Re: Why does this work on Xcode ??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-10 11:18 -0700
              Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-10 21:05 +0200
                Re: Why does this work on Xcode ??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-22 10:28 -0700
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-22 19:50 +0200
                Re: Why does this work on Xcode ??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-08-22 23:45 +0100
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-23 07:22 +0200
                Re: Why does this work on Xcode ??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-08-23 13:12 +0100
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-23 16:02 +0200
                Re: Why does this work on Xcode ??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-09-18 08:50 -0700
                Re: Why does this work on Xcode ??? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-08-23 09:28 -0400
                Re: Why does this work on Xcode ??? David Brown <david.brown@hesbynett.no> - 2019-08-23 16:37 +0200
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-23 23:07 +0200
                Re: Why does this work on Xcode ??? Richard Damon <Richard@Damon-Family.org> - 2019-08-23 19:10 -0400
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-24 06:49 +0200
                Re: Why does this work on Xcode ??? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-08-23 19:49 -0400
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-24 06:45 +0200
                Re: Why does this work on Xcode ??? David Brown <david.brown@hesbynett.no> - 2019-08-25 12:06 +0200
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-25 13:25 +0200
                Re: Why does this work on Xcode ??? David Brown <david.brown@hesbynett.no> - 2019-08-25 15:11 +0200
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-25 17:12 +0200
                Re: Why does this work on Xcode ??? David Brown <david.brown@hesbynett.no> - 2019-08-25 23:32 +0200
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-26 11:51 +0200
                Re: Why does this work on Xcode ??? David Brown <david.brown@hesbynett.no> - 2019-08-26 13:26 +0200
                Re: Why does this work on Xcode ??? David Brown <david.brown@hesbynett.no> - 2019-08-25 11:36 +0200
                Re: Why does this work on Xcode ??? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-25 13:27 +0200
                Re: Why does this work on Xcode ??? David Brown <david.brown@hesbynett.no> - 2019-08-25 15:15 +0200
                Re: Why does this work on Xcode ??? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-08-26 00:43 -0400
                Re: Why does this work on Xcode ??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-24 04:58 -0700
                Re: Why does this work on Xcode ??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-26 09:53 -0700
                Re: Why does this work on Xcode ??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-28 18:03 -0700
          Re: Why does this work on Xcode ??? Öö Tiib <ootiib@hot.ee> - 2019-07-19 00:20 -0700
          Re: Why does this work on Xcode ??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-09 07:41 -0700
      Re: Why does this work on Xcode ??? Bonita Montero <Bonita.Montero@gmail.com> - 2019-08-24 19:49 +0200
    Re: Why does this work on Xcode ??? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-07-21 11:41 +0000
      Re: Why does this work on Xcode ??? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-08-10 09:29 -0700

csiph-web