text: #ifndef BOOST_CLBL_TRTS_DETAIL_FORWARD_DECLARATIONS
  #define BOOST_CLBL_TRTS_DETAIL_FORWARD_DECLARATIONS
  #include <boost/callable_traits/detail/config.hpp>
  #include <boost/callable_traits/detail/default_callable_traits.hpp>
  
  namespace boost { namespace callable_traits { namespace detail {
  
  template<typename T>
  struct function;
  
  template<typename T>
  struct has_normal_call_operator
  {
      template<typename N, N Value>
      struct check { check(std::nullptr_t) {} };
  
      template<typename U>
      static std::int8_t test(
          check<decltype(&U::operator()), &U::operator()>);
  
      template<typename>
      static std::int16_t test(...);
  
      static constexpr bool value =
          sizeof(test<T>(nullptr)) == sizeof(std::int8_t);
  };
  
  struct callable_dummy {
      void operator()() {}
  };
  
  template<typename T>
  using default_to_function_object = typename std::conditional<
      has_normal_call_operator<T>::value,
      T, callable_dummy>::type;
  
  template<typename T>
  struct pmf;
  
  template<typename T>
  struct pmd;
  
  template<typename F, typename T = typename std::remove_reference<F>::type>
  using function_object_base = typename std::conditional<
      has_normal_call_operator<T>::value,
      pmf<decltype(&default_to_function_object<T>::operator())>,
      default_callable_traits<T>>::type;
  
  template<typename T, typename Base = function_object_base<T>>
  struct function_object;
  
  }}} // namespace boost::callable_traits::detail
  
  #endif // #ifndef BOOST_CLBL_TRTS_DETAIL_FORWARD_DECLARATIONS
  