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Re: On endianness, many #ifdefs, and the need thereof

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Daniel <danielaparker@gmail.com> wrote:
>> > > > static constexpr bool little_endianess(int num = 1) noexcept
>> > > > {
>> > > >     return *reinterpret_cast<char*>(&num) == 1;
>> > > > }

>> > The example is from the nlohmann json library, where I first saw it, 
>> > https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp#L5159, 
>> > and it does compile.
>> 
>> On what compiler does that compile:
>> 
>>     constexpr bool b = nlohmann:detail::little_endianess();
>>  
>> ???
> 
> That wouldn't :-) little_endianess() is a static member function of the 
> template class binary_reader. I meant that the function compiles in the 
> contexts in which it is used in nlohmann's library, it is used after all. But 
> the result can't be assigned to a constexpr bool. 

I find it surprising that it will compile with that 'constexpr'
modifier. I have always had the understanding that a constexpr
function can only contain code that could at least in theory be
evaluated at compile time (even if it actually isn't). At the very
least the potential must be there.

Taking the address of a variable and dereferencing it doesn't
sound like something that should be doable at compile time,
and therefore it sounds like it wouldn't be allowed in a
constexpr function (in the same way as it isn't allowed
eg. as a non-type template parameter).

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On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-02 04:00 -0700
  Re: On endianness, many #ifdefs, and the need thereof David Brown <david.brown@hesbynett.no> - 2019-10-02 13:26 +0200
    Re: On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-02 08:59 -0700
  Re: On endianness, many #ifdefs, and the need thereof Öö Tiib <ootiib@hot.ee> - 2019-10-02 05:42 -0700
  Re: On endianness, many #ifdefs, and the need thereof Juha Nieminen <nospam@thanks.invalid> - 2019-10-02 12:53 +0000
    Re: On endianness, many #ifdefs, and the need thereof David Brown <david.brown@hesbynett.no> - 2019-10-02 15:05 +0200
      Re: On endianness, many #ifdefs, and the need thereof scott@slp53.sl.home (Scott Lurndal) - 2019-10-02 13:54 +0000
        Re: On endianness, many #ifdefs, and the need thereof Keith Thompson <kst-u@mib.org> - 2019-10-02 12:54 -0700
          Re: On endianness, many #ifdefs, and the need thereof scott@slp53.sl.home (Scott Lurndal) - 2019-10-02 20:16 +0000
        Re: On endianness, many #ifdefs, and the need thereof David Brown <david.brown@hesbynett.no> - 2019-10-03 09:48 +0200
    Re: On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-02 07:52 -0700
      Re: On endianness, many #ifdefs, and the need thereof Öö Tiib <ootiib@hot.ee> - 2019-10-02 08:04 -0700
        Re: On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-02 08:31 -0700
          Re: On endianness, many #ifdefs, and the need thereof Juha Nieminen <nospam@thanks.invalid> - 2019-10-02 21:32 +0000
      Re: On endianness, many #ifdefs, and the need thereof Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-10-03 11:33 +0000
        Re: On endianness, many #ifdefs, and the need thereof David Brown <david.brown@hesbynett.no> - 2019-10-03 13:46 +0200
          Re: On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-03 05:56 -0700
            Re: On endianness, many #ifdefs, and the need thereof scott@slp53.sl.home (Scott Lurndal) - 2019-10-03 13:17 +0000
              Re: On endianness, many #ifdefs, and the need thereof David Brown <david.brown@hesbynett.no> - 2019-10-03 16:03 +0200
                Re: On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-03 07:13 -0700
          Re: On endianness, many #ifdefs, and the need thereof Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-10-03 18:51 +0000
          Re: On endianness, many #ifdefs, and the need thereof Keith Thompson <kst-u@mib.org> - 2019-10-03 14:28 -0700
            Re: On endianness, many #ifdefs, and the need thereof David Brown <david.brown@hesbynett.no> - 2019-10-04 10:11 +0200
              Re: On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-04 09:00 -0700
        Re: On endianness, many #ifdefs, and the need thereof Paavo Helde <myfirstname@osa.pri.ee> - 2019-10-03 14:46 +0300
        Re: On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-03 05:40 -0700
  Re: On endianness, many #ifdefs, and the need thereof Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-02 15:10 +0200
  Re: On endianness, many #ifdefs, and the need thereof Barry Schwarz <schwarzb@dqel.com> - 2019-10-02 08:33 -0700
    Re: On endianness, many #ifdefs, and the need thereof David Brown <david.brown@hesbynett.no> - 2019-10-03 09:54 +0200
  Re: On endianness, many #ifdefs, and the need thereof "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-10-02 19:35 +0200
    Re: On endianness, many #ifdefs, and the need thereof Daniel <danielaparker@gmail.com> - 2019-10-02 15:39 -0700
  Re: On endianness, many #ifdefs, and the need thereof "Oliver S." <Follow.Me@gmx.net> - 2019-10-02 19:59 +0200

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