MSVC 1916 does not have a good constexpr 14 support about config

[jzmaddock]

Sorry for the delay in getting around to this!

This is a weird one, and I'm not completely convinced msvc is at fault yet. If I change the == operator to:

template <class Derived, class TypeInfo>
BOOST_CXX14_CONSTEXPR inline bool operator == (const type_index_facade<Derived, TypeInfo>& lhs, const type_index_facade<Derived, TypeInfo>& rhs) BOOST_NOEXCEPT {
   constexpr Derived const& d1 = static_cast<Derived const&>(lhs);
   constexpr Derived const& d2 = static_cast<Derived const&>(rhs);
   return d1.equal(d2);
}

Then obviously it can only be used in a constexpr context, but even then both gcc and clang issue (completely inscrutable) errors. But work just fine if I remove the constexpr from d1 and d2.

Confused yours...