Hi Andrey,
I'm seeing compilation errors coming from Boost.Fusion headers on Sandia-intel-17.0-c++14:
http://www.boost.org/development/tests/develop/developer/output/Sandia-intel...
Notably, the same tests compile fine in C++11 mode on the same compiler, which makes me think that is related to C++14 mode specifically. Looking at the code, it seems the compiler makes constexpr functions implicitly const-qualified even though it shouldn't in C++14 mode, so it's likely a compiler bug. Still, is it possible to add a workaround? I think the bug affects not only fusion, i.e. updating config is better.
Is it possible to override BOOST_CXX14_CONSTEXPR somehow?
Only if you define and use your own similar macro in Boost.Fusion. Or if we decide that C++14 constexpr is broken enough in the compiler to warrant the change in Boost.Config. The compiler passes all Boost.Config tests[1] in C++14 mode, so I guess it supports C++14 mostly ok.
[1]: http://www.boost.org/development/tests/develop/developer/config.html It seems the test is not enough about such case. I opened a pull-request that updates config_test: https://github.com/boostorg/config/pull/104 .
Thanks, Kohei Takahashi