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/boos...) 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