Class type

include/boost/asio/query.hpp:198–210

  {
#if defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
    struct type
    {
      template <typename P>
      auto query(P&& p)
        noexcept(
          noexcept(
            declval<conditional_t<true, T, P>>().query(static_cast<P&&>(p))
          )
        )
        -> decltype(
          declval<conditional_t<true, T, P>>().query(static_cast<P&&>(p))
        );
    };
#else // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
    typedef T type;
#endif // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)