macro BOOST_HAS_CONCEPTS not work + namespace for concepts

From: Gero Peterhoff (g.peterhoff_at_[hidden])
Date: 2023-02-19 12:24:54

Hi,
1) the macro BOOST_HAS_CONCEPTS from <boost/config.hpp> (https://www.boost.org/doc/libs/1_81_0/libs/config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_possible_c___future_features) not work:
https://godbolt.org/z/3G8vTrjcf


2) namespace for concepts
Would it make sense to introduce a namespace *only* for concepts to avoid naming conflicts with existing classes? boost::concepts would be useful, but this is already used by the concept-check-library. Then would boost::Concepts be a good choice or could boost::concepts still be used? EG

namespace boost
{
template <typename Type> struct my_trait ...;

#if !defined(BOOST_NO_CXX17_INLINE_VARIABLES)
template <typename Type> inline constexpr bool my_trait_v = my_trait<Type>::value;
#endif

#if concepts available
namespace Concepts
{
template <typename Type> concept my_concept = my_trait_v<Type>;
} // Concepts
#endif
} // boost


thx
Gero