Re: C++, Ada, ...

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.arch.embedded
Subject	Re: C++, Ada, ...
Date	2021-04-19 08:52 +0200
Organization	A noiseless patient Spider
Message-ID	<s5j9bk$ced$1@dont-email.me> (permalink)
References	(4 earlier) <ie34olFmda9U1@mid.individual.net> <s5hq48$k2e$1@dont-email.me> <WU_eI.237389$KHwf.63256@fx25.ams4> <s5i441$tro$1@dont-email.me> <Kd2fI.273342$zV01.166134@fx49.ams4>

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On 19/04/2021 00:17, Tom Gardner wrote:
> On 18/04/21 21:17, David Brown wrote:
>> On 18/04/2021 20:30, Tom Gardner wrote:
>>> On 18/04/21 18:26, David Brown wrote:
>>>> C++ has got a lot stronger at compile-time work in recent versions. 
>>>> Not
>>>> only have templates got more powerful, but we've got "concepts" (named
>>>> sets of features or requirements for types), constexpr functions (that
>>>> can be evaluated at compile time or runtime), consteval functions (that
>>>> must be evaluated at compile time), constinit data (that must have
>>>> compile-time constant initialisers), etc.  And constants determined at
>>>> compile-time are not restricted to scaler or simple types.
>>>
>>> Sounds wordy ;)
>>
>> Have you looked at the C++ standards documents?  There are more than a
>> few words there!
> 
> No. I value my sanity.

I have looked at it, and come back as sane as ever (apart from the
pencils up my nose and underpants on my head).  But I've worked up to it
through many versions of the C standards.

More seriously, if I need to look up any details of C or C++, I find
<https://en.cppreference.com/w/> vastly more user-friendly.

> 
> 
>> I'm not suggesting C++ is a perfect language - not by a long way.  It
>> has plenty of ugliness, and in this thread we've covered several points
>> where Ada can do something neater and clearer than you can do it in C++.
>>
>> But it's a good thing that it has more ways for handling things at
>> compile time.  In many of my C projects, I have had Python code for
>> pre-processing, for computing tables, and that kind of thing.  With
>> modern C++, these are no longer needed.
> 
> The useful question is not whether something is good,
> but whether there are better alternatives. "Better",
> of course, can include /anything/ relevant!
> 

Yes - and "better" is usually highly subjective.

In the case of compile-time calculations, modern C++ is certainly better
than older C++ versions or C (or, AFAIK, Ada).  It can't do everything
that I might do with external Python scripts - it can't do code
generation, or make tables that depend on multiple source files, or make
CRC checks for the final binary.  But it can do some things that
previously required external scripts, and that's nice.

> 
> 
>> An odd thing about the compile-time calculation features of C++ is that
>> they came about partly by accident, or unforeseen side-effects.  Someone
>> discovered that templates with integer parameters could be used to do
>> quite a lot of compile-time calculations.  The code was /really/ ugly,
>> slow to compile, limited in scope.  But people were finding use for it.
>>   So the motivation for "constexpr" was that programmers were already
>> doing compile-time calculations, and so it was best to let them do it in
>> a nicer way.
> 
> Infamously, getting a valid C++ program that cause the
> compiler to generate the sequence of prime numbers during
> compilation came as an unpleasant /surprise/ to the C++
> standards committee.

I don't believe that the surprise was "unpleasant" - it's just something
they hadn't considered.  (I'm not even sure of that either - my feeling
is that this is an urban myth, or at least a story exaggerated in the
regular retelling.)

> 
> The code is short; whether it is ugly is a matter of taste!
> https://en.wikibooks.org/wiki/C%2B%2B_Programming/Templates/Template_Meta-Programming#History_of_TMP
> 

Template-based calculations were certainly very convoluted - they needed
a functional programming style structure but with much more awkward
syntax (and at the height of their "popularity", horrendous compiler
error messages when you made a mistake - that too has improved greatly).
 And that is why constexpr (especially in latest versions) is so much
better.

Template-based calculations are a bit like trying to do calculations and
data structures in LaTeX.  It is all possible, but it doesn't roll off
the tongue very easily.

(I wonder if anyone else understands the pencil and underpants
reference.  I am sure Tom does.)

Thread

C++, Ada, ... pozz <pozzugno@gmail.com> - 2021-04-17 17:48 +0200
  Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-17 18:45 +0200
    Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-17 19:55 +0100
      Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-18 12:53 +0200
        Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-18 18:48 +0300
          Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-18 18:59 +0200
            Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-19 13:51 +0300
              Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-19 14:22 +0200
                Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-19 19:16 +0300
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-19 22:19 +0200
                Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-20 01:03 +0300
                Re: C++, Ada, ... Richard Damon <Richard@Damon-Family.org> - 2021-04-19 18:09 -0400
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-20 06:58 +0200
                Re: C++, Ada, ... Paul Rubin <no.email@nospam.invalid> - 2021-04-19 23:18 -0700
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-20 09:36 +0200
              Re: C++, Ada, ... Paul Rubin <no.email@nospam.invalid> - 2021-04-19 12:20 -0700
                Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-20 00:26 +0300
                Re: C++, Ada, ... Paul Rubin <no.email@nospam.invalid> - 2021-04-19 16:01 -0700
                Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-20 10:47 +0300
                Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-19 23:30 +0100
    Re: C++, Ada, ... Clifford Heath <no.spam@please.net> - 2021-04-18 08:29 +1000
    Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-18 10:39 +0300
      Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-18 14:59 +0200
        Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-18 19:23 +0300
          Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-18 19:26 +0200
            Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-18 19:29 +0100
              Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-18 22:23 +0200
                Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-18 23:09 +0100
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-19 08:56 +0200
                Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-19 14:04 +0300
                Re: C++, Ada, ... Dimiter_Popoff <dp@tgi-sci.com> - 2021-04-19 15:16 +0300
                Re: C++, Ada, ... Paul Rubin <no.email@nospam.invalid> - 2021-04-19 12:47 -0700
                Re: C++, Ada, ... Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-04-20 00:37 +0300
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-20 07:50 +0200
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-19 14:26 +0200
            Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-18 19:30 +0100
              Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-18 22:17 +0200
                Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-18 23:17 +0100
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-19 08:52 +0200
                Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-19 10:08 +0100
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-19 12:15 +0200
                Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-19 12:00 +0100
                Re: C++, Ada, ... Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2021-04-19 16:15 +0300
                Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-19 15:43 +0200
    Re: C++, Ada, ... pozz <pozzugno@gmail.com> - 2021-04-19 18:38 +0200
      Re: C++, Ada, ... Paul Rubin <no.email@nospam.invalid> - 2021-04-19 10:48 -0700
      Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-19 19:33 +0100
        Re: C++, Ada, ... Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2021-04-20 15:09 +0300
          Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-20 15:29 +0100
      Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-19 22:48 +0200
        Re: C++, Ada, ... pozz <pozzugno@gmail.com> - 2021-04-19 23:17 +0200
          Re: C++, Ada, ... Paul Rubin <no.email@nospam.invalid> - 2021-04-19 15:55 -0700
            Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-20 08:21 +0200
          Re: C++, Ada, ... David Brown <david.brown@hesbynett.no> - 2021-04-20 08:20 +0200
  Re: C++, Ada, ... Dave Nadler <drn@nadler.com> - 2021-04-17 21:07 -0400
    Re: C++, Ada, ... Don Y <blockedofcourse@foo.invalid> - 2021-04-17 18:53 -0700
    Re: C++, Ada, ... Tom Gardner <spamjunk@blueyonder.co.uk> - 2021-04-18 09:42 +0100
  Re: C++, Ada, ... dalai lamah <antonio12358@hotmail.com> - 2021-04-18 14:39 +0200

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