Cannot link shared library in C++14 or later

[jbeich]

After 7b6dcf6 the following doesn't work, breaking a number of consumers. Adding -DBOOST_NO_CXX14_CONSTEXPR appears to help. Is this intentional?

$ cat >a.cc
#include <boost/system/error_code.hpp>

int main()
{
  return 0;
}

$ pkg info -x boost
boost-libs-1.68.0.beta1.rc2

$ c++ -v
FreeBSD clang version 6.0.1 (tags/RELEASE_601/final 335540) (based on LLVM 6.0.1)
Target: x86_64-unknown-freebsd12.0
Thread model: posix
InstalledDir: /usr/bin

$ c++ a.cc -std=c++14 -I/usr/local/include -L/usr/local/lib -lboost_system
/usr/bin/ld: error: undefined symbol: boost::system::detail::generic_category_instance
>>> referenced by a.cc
>>>               /tmp/a-912c13.o:(boost::system::generic_category())
c++: error: linker command failed with exit code 1 (use -v to see invocation)

[jbeich]

Ah, Boost.System itself has to be built with -std=c++14. I was building with -std=gnu++11, so Boost.Config auto-enabled cxx11_constexpr.

[pdimov]

Yes. I think I support the reverse case, linking from C++11 to a C++14-built System, but not this one. (And linking from 03 to 11 should work in both directions.) But in general this kind of thing (mixing C++ dialects) is unlikely to work.