[boost] Re: Are BOOST_STATIC_ASSERT() and BOOST_STATIC_CONSTANT() still necessary?

Daniela Engert wrote:

What's really bugging me is the use of BOOST_CONSTEXPR_OR_CONST at namespace scope in header files. You can easily end up in TU-local entities which are deprecated in traditional compilations, and outright forbidden in modules / header units. I have replaced them with BOOST_INLINE_CONSTEXPR in some libraries to get an actually usable module Boost.

There was no good way to have a namespace scope constant before C++17, so it's not that surprising that every library written before that is technically broken.