Example does not compile VS C++17

[simonrenger]

The example:

#include <iostream>
#include <string>
#include "boost/pfr/precise.hpp"

struct some_person {
    std::string name;
    unsigned birth_year;
};

int main() {
    some_person val{"Edgar Allan Poe", 1809};

    std::cout << boost::pfr::get<0>(val)                // No macro!
        << " was born in " << boost::pfr::get<1>(val);  // Works with any aggregate initializables!
}

Does not compile:

1>a:\cpp\reftest\reftest\ext\include\boost\pfr\detail\fields_count.hpp(209): error C2338: ====================> Boost.PFR: Types with user specified constructors (non-aggregate initializable types) are not supported.
1>a:\cpp\reftest\reftest\ext\include\boost\pfr\detail\core17_generated.hpp(1036): note: see reference to function template instantiation 'size_t boost::pfr::detail::fields_count<T>(void) noexcept' being compiled
1>        with
1>        [
1>            T=some_person
1>        ]
1>a:\cpp\reftest\reftest\ext\include\boost\pfr\precise\core.hpp(50): note: see reference to function template instantiation 'auto boost::pfr::detail::tie_as_tuple<T>(T &) noexcept' being compiled
1>        with
1>        [
1>            T=some_person
1>        ]
1>a:\cpp\reftest\reftest\src\main.cpp(62): note: see reference to function template instantiation 'decltype(auto) boost::pfr::get<0,some_person>(T &) noexcept' being compiled
1>        with
1>        [
1>            T=some_person
1>        ]
1>a:\cpp\reftest\reftest\ext\include\boost\pfr\detail\fields_count.hpp(214): error C2338: ====================> Boost.PFR: If there's no other failed static asserts then something went wrong. Please report this issue to the github along with the structure you're reflecting.
1>a:\cpp\reftest\reftest\ext\include\boost\pfr\detail\sequence_tuple.hpp(114): error C2338: ====================> Boost.PFR: Tuple index out of bounds
1>a:\cpp\reftest\reftest\ext\include\boost\pfr\precise\core.hpp(50): note: see reference to function template instantiation 'decltype(auto) boost::pfr::detail::sequence_tuple::get<0,>(boost::pfr::detail::sequence_tuple::tuple<> &&) noexcept' being compiled
1>a:\cpp\reftest\reftest\ext\include\boost\pfr\detail\sequence_tuple.hpp(115): error C2672: 'get_impl': no matching overloaded function found
1>a:\cpp\reftest\reftest\ext\include\boost\pfr\detail\sequence_tuple.hpp(113): error C2784: 'T &boost::pfr::detail::sequence_tuple::get_impl(boost::pfr::detail::sequence_tuple::base_from_member<N,T> &) noexcept': could not deduce template argument for 'boost::pfr::detail::sequence_tuple::base_from_member<0,T> &' from 'boost::pfr::detail::sequence_tuple::tuple<>'
1>a:\cpp\reftest\reftest\ext\include\boost\pfr\detail\sequence_tuple.hpp(51): note: see declaration of 'boost::pfr::detail::sequence_tuple::get_impl'
1>a:\cpp\reftest\reftest\src\main.cpp(62): error C2679: binary '<<': no operator found which takes a right-hand operand of type 'void' (or there is no acceptable conversion)

Compiler:

/JMC /permissive- /MP /GS /W3 /Zc:wchar_t /I"A:\cpp\reftest\reftest\ext\include\" /I"A:\cpp\reftest\\include\" /I"C:\Program Files (x86)\Visual Leak Detector\include" /ZI /Gm- /Od /sdl /Fd"x64\Debug\vc141.pdb" /Zc:inline /fp:precise /D "_MBCS" /errorReport:prompt /WX- /Zc:forScope /RTC1 /Gd /MDd /std:c++17 /FC /Fa"x64\Debug\" /EHsc /nologo /Fo"x64\Debug\" /Fp"x64\Debug\reftest.pch" /diagnostics:classic 

[apolukhin]

I've added more platforms and MSVC flags into the CI runs in commit apolukhin@e993693

No issues were found. Probably your issue was fixed in commit apolukhin@9520aa7 .

@simonrenger could you please double check that the issue still exist with the latest develop version of the library?

[simonrenger]

I got latest of the develop branch... but I still get a compiler error

Just to make sure I have created an empty C++ Solution with VS17

The error remains:

1>------ Build started: Project: magic_getTest, Configuration: Debug x64 ------
1>main.cpp
1>a:\cpp\magic_get\include\boost\pfr\detail\fields_count.hpp(210): error C2338: ====================> Boost.PFR: Types with user specified constructors (non-aggregate initializable types) are not supported.
1>a:\cpp\magic_get\include\boost\pfr\detail\core17_generated.hpp(1036): note: see reference to function template instantiation 'size_t boost::pfr::detail::fields_count<T>(void) noexcept' being compiled
1>        with
1>        [
1>            T=some_person
1>        ]
1>a:\cpp\magic_get\include\boost\pfr\precise\core.hpp(51): note: see reference to function template instantiation 'auto boost::pfr::detail::tie_as_tuple<T>(T &) noexcept' being compiled
1>        with
1>        [
1>            T=some_person
1>        ]
1>a:\cpp\magic_gettest\magic_gettest\main.cpp(13): note: see reference to function template instantiation 'decltype(auto) boost::pfr::get<0,some_person>(T &) noexcept' being compiled
1>        with
1>        [
1>            T=some_person
1>        ]
1>a:\cpp\magic_get\include\boost\pfr\detail\fields_count.hpp(215): error C2338: ====================> Boost.PFR: If there's no other failed static asserts then something went wrong. Please report this issue to the github along with the structure you're reflecting.
1>a:\cpp\magic_get\include\boost\pfr\detail\sequence_tuple.hpp(115): error C2338: ====================> Boost.PFR: Tuple index out of bounds
1>a:\cpp\magic_get\include\boost\pfr\precise\core.hpp(51): note: see reference to function template instantiation 'decltype(auto) boost::pfr::detail::sequence_tuple::get<0,>(boost::pfr::detail::sequence_tuple::tuple<> &&) noexcept' being compiled
1>a:\cpp\magic_get\include\boost\pfr\detail\sequence_tuple.hpp(116): error C2672: 'get_impl': no matching overloaded function found
1>a:\cpp\magic_get\include\boost\pfr\detail\sequence_tuple.hpp(114): error C2784: 'T &boost::pfr::detail::sequence_tuple::get_impl(boost::pfr::detail::sequence_tuple::base_from_member<N,T> &) noexcept': could not deduce template argument for 'boost::pfr::detail::sequence_tuple::base_from_member<0,T> &' from 'boost::pfr::detail::sequence_tuple::tuple<>'
1>a:\cpp\magic_get\include\boost\pfr\detail\sequence_tuple.hpp(52): note: see declaration of 'boost::pfr::detail::sequence_tuple::get_impl'
1>a:\cpp\magic_gettest\magic_gettest\main.cpp(13): error C2679: binary '<<': no operator found which takes a right-hand operand of type 'void' (or there is no acceptable conversion)
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(508): note: could be 'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_streambuf<char,std::char_traits<char>> *)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(480): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(const void *)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(460): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(long double)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(440): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(double)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(420): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(float)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(400): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned __int64)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(380): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(__int64)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(360): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned long)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(340): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(long)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(320): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned int)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(295): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(int)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(275): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned short)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(241): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(short)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(221): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(bool)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(215): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::ios_base &(__cdecl *)(std::ios_base &))'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(209): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_ios<char,std::char_traits<char>> &(__cdecl *)(std::basic_ios<char,std::char_traits<char>> &))'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(204): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_ostream<char,std::char_traits<char>> &(__cdecl *)(std::basic_ostream<char,std::char_traits<char>> &))'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(502): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<<void>(std::nullptr_t)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(702): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const char *)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(749): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(787): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const char *)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(834): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(960): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const signed char *)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(967): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,signed char)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(974): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const unsigned char *)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(981): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,unsigned char)'
1>c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\ostream(1047): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const std::error_code &)'
1>a:\cpp\magic_gettest\magic_gettest\main.cpp(14): note: while trying to match the argument list '(std::ostream, void)'
1>a:\cpp\magic_get\include\boost\pfr\detail\sequence_tuple.hpp(114): error C2784: 'T &boost::pfr::detail::sequence_tuple::get_impl(boost::pfr::detail::sequence_tuple::base_from_member<N,T> &) noexcept': could not deduce template argument for 'boost::pfr::detail::sequence_tuple::base_from_member<1,T> &' from 'boost::pfr::detail::sequence_tuple::tuple<>'
1>a:\cpp\magic_get\include\boost\pfr\detail\sequence_tuple.hpp(52): note: see declaration of 'boost::pfr::detail::sequence_tuple::get_impl'
1>Done building project "magic_getTest.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

[apolukhin]

@simonrenger could you please run the tests using b2.exe from Boost? I'd like to make sure, that the failure is caused by a change in MSVC internals, rather than by some flag or environmental change.

Do the other examples compile?

[dimarusyy]

I'm getting the same error. See the log in attached file after feeding tests to b2.
log.zip

[andj1210]

The error appears by /permissive- in VS2017, in VS2019 its always persent!
See: https://github.com/apolukhin/magic_get/issues/21#issuecomment-473656962

[janwilmans]

This specific example does work, when you make sure /std:c++17 is specified and /permissive- is not specified.

However, the tests from test/flat/flat_for_each_field.cpp do not compile on vs2017 nor vs2019 even with /std:latest. Looking at the logs these tests are also not running in CI, I see destructuring_tie.cpp passing, but none of the other tests below:

core.cpp
destructuring_tie.cpp  // this is the only test that I see running in the log file on appveyor 
flat_for_each_field.cpp
flat_motivating_example.cpp
flat_motivating_example2.cpp
flat_tuple_size.cpp
flat_tuple_size_on_bitfields.cpp
flat_tuple_size_on_non_aggregate.cpp

We should close this issue, as the example here is actually working, I've opened a new issue #37 for the CI problem.

[apolukhin]

Closing in favor of #37

[apolukhin]

I'd appreciate reporting the /std:c++17 + /permissive- issue to the MSVC development team if anyone is interested in that combination of flags.

[janwilmans]

I'd be happy to report anything, however, /permissive- means to the compiler adheres strictly to the standard's rules and disables microsoft specific extensions. That said, a lot has changed during the last 2 years in the msvc compiler. They finally support two-phase-lookup and expression SFINAE and according to their website, they were fully c++17 compliant last year.