[boost] [config] Configuring for C++14 and later library features.

Subject: [boost] [config] Configuring for C++14 and later library features.
From: John Maddock (jz.maddock_at_[hidden])
Date: 2015-04-24 08:32:36

Folks,

I have an open PR for adding BOOST_NO_CXX14_INTEGER_SEQUENCE 
(https://github.com/boostorg/config/pull/58).

Unfortunately, the correct way to check for std::integer_sequence is to 
include <utility> and then check for __cpp_lib_integer_sequence.  The 
problem is that we went to some lengths to remove dependencies on 
<utility> in https://github.com/boostorg/config/pull/40.  Further, if we 
get requests for more such feature-detection macros, we would end up 
including the whole std lib (see 
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3745#recs.cpp14).

This doesn't look acceptable to me, but what to do?  The only solution I 
can see is to simply not support these features in Boost.Config, but 
rather rely on users needing these features checking the std detection 
macros directly.  Which will work up until someone implements a feature 
without defining the appropriate macro :(

Thoughts?

Thanks, John.