Hi John, i miss these for C++17/20/23 in boost/config. Can you retrofit this? thx Gero It could look like this: see https://en.cppreference.com/w/cpp/feature_test#__cpp_constexpr #if (__cpp_constexpr < 201703L) #define BOOST_NO_CXX17_CONSTEXPR #endif #if defined(BOOST_NO_CXX17_CONSTEXPR) #define BOOST_CXX17_CONSTEXPR #else #define BOOST_CXX17_CONSTEXPR constexpr #endif #if (__cpp_constexpr < 202002L) #define BOOST_NO_CXX20_CONSTEXPR #endif #if defined(BOOST_NO_CXX20_CONSTEXPR) #define BOOST_CXX20_CONSTEXPR #else #define BOOST_CXX20_CONSTEXPR constexpr #endif #if (__cpp_constexpr < 202207L) #define BOOST_NO_CXX23_CONSTEXPR #endif #if defined(BOOST_NO_CXX23_CONSTEXPR) #define BOOST_CXX23_CONSTEXPR #else #define BOOST_CXX23_CONSTEXPR constexpr #endif