text: //  (C) Copyright 2009-2011 Frederic Bron, Robert Stewart, Steven Watanabe & Roman Perepelitsa.
  //
  //  Use, modification and distribution are subject to the Boost Software License,
  //  Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
  //  http://www.boost.org/LICENSE_1_0.txt).
  //
  //  See http://www.boost.org/libs/type_traits for most recent version including documentation.
  
  #include <boost/config.hpp>
  #include <boost/type_traits/detail/config.hpp>
  
  #if defined(BOOST_TT_HAS_ACCURATE_BINARY_OPERATOR_DETECTION)
  
  #include <boost/type_traits/integral_constant.hpp>
  #include <boost/type_traits/make_void.hpp>
  #include <boost/type_traits/is_convertible.hpp>
  #include <boost/type_traits/is_void.hpp>
  #include <boost/type_traits/add_reference.hpp>
  #include <utility>
  
  #ifdef BOOST_GCC
  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wdeprecated"
  #endif
  #if defined(BOOST_MSVC)
  #   pragma warning ( push )
  #   pragma warning ( disable : 4804)
  #endif
  
  namespace boost
  {
  
     namespace binary_op_detail {
  
        struct dont_care;
  
        template <class T, class Ret, class = void>
        struct BOOST_JOIN(BOOST_TT_TRAIT_NAME, _ret_imp) : public boost::false_type {};
  
        template <class T, class Ret>
        struct BOOST_JOIN(BOOST_TT_TRAIT_NAME, _ret_imp)<T, Ret, typename boost::make_void<decltype(BOOST_TT_TRAIT_OP std::declval<typename add_reference<T>::type>()) >::type>
           : public boost::integral_constant<bool, ::boost::is_convertible<decltype(BOOST_TT_TRAIT_OP std::declval<typename add_reference<T>::type>() ), Ret>::value> {};
  
        template <class T, class = void >
        struct BOOST_JOIN(BOOST_TT_TRAIT_NAME, _void_imp) : public boost::false_type {};
  
        template <class T>
        struct BOOST_JOIN(BOOST_TT_TRAIT_NAME, _void_imp)<T, typename boost::make_void<decltype(BOOST_TT_TRAIT_OP std::declval<typename add_reference<T>::type>())>::type>
           : public boost::integral_constant<bool, ::boost::is_void<decltype(BOOST_TT_TRAIT_OP std::declval<typename add_reference<T>::type>())>::value> {};
  
        template <class T, class = void>
        struct BOOST_JOIN(BOOST_TT_TRAIT_NAME, _dc_imp) : public boost::false_type {};
  
        template <class T>
        struct BOOST_JOIN(BOOST_TT_TRAIT_NAME, _dc_imp)<T, typename boost::make_void<decltype(BOOST_TT_TRAIT_OP std::declval<typename add_reference<T>::type>() )>::type>
           : public boost::true_type {};
  
     }
  
     template <class T, class Ret = boost::binary_op_detail::dont_care>
     struct BOOST_TT_TRAIT_NAME : public boost::binary_op_detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _ret_imp) <T, Ret> {};
     template <class T>
     struct BOOST_TT_TRAIT_NAME<T, void> : public boost::binary_op_detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _void_imp) <T> {};
     template <class T>
     struct BOOST_TT_TRAIT_NAME<T, boost::binary_op_detail::dont_care> : public boost::binary_op_detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _dc_imp) <T> {};
  
  
  }
  
  #ifdef BOOST_GCC
  #pragma GCC diagnostic pop
  #endif
  #if defined(BOOST_MSVC)
  #   pragma warning ( pop )
  #endif
  
  #else
  
  #include <boost/type_traits/detail/yes_no_type.hpp>
  #include <boost/type_traits/integral_constant.hpp>
  #include <boost/type_traits/is_const.hpp>
  #include <boost/type_traits/is_fundamental.hpp>
  #include <boost/type_traits/is_integral.hpp>
  #include <boost/type_traits/is_pointer.hpp>
  #include <boost/type_traits/is_same.hpp>
  #include <boost/type_traits/is_void.hpp>
  #include <boost/type_traits/remove_cv.hpp>
  #include <boost/type_traits/remove_pointer.hpp>
  #include <boost/type_traits/remove_reference.hpp>
  
  // cannot include this header without getting warnings of the kind:
  // gcc:
  //    warning: value computed is not used
  //    warning: comparison between signed and unsigned integer expressions
  // msvc:
  //    warning C4146: unary minus operator applied to unsigned type, result still unsigned
  //    warning C4804: '-' : unsafe use of type 'bool' in operation
  // cannot find another implementation -> declared as system header to suppress these warnings.
  #if defined(__GNUC__)
  #   pragma GCC system_header
  #elif defined(BOOST_MSVC)
  #   pragma warning ( push )
  #   pragma warning ( disable : 4146 4804 4913 4244 4800)
  #   if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000)
  #       pragma warning ( disable : 6334)
  #   endif
  #   if BOOST_WORKAROUND(_MSC_VER, >= 1913)
  #       pragma warning ( disable : 4834)
  #   endif
  #endif
  
  
  
  namespace boost {
  namespace detail {
  
  // This namespace ensures that argument-dependent name lookup does not mess things up.
  namespace BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl) {
  
  // 1. a function to have an instance of type T without requiring T to be default
  // constructible
  template <typename T> T &make();
  
  
  // 2. we provide our operator definition for types that do not have one already
  
  // a type returned from operator BOOST_TT_TRAIT_OP when no such operator is
  // found in the type's own namespace (our own operator is used) so that we have
  // a means to know that our operator was used
  struct no_operator { };
  
  // this class allows implicit conversions and makes the following operator
  // definition less-preferred than any other such operators that might be found
  // via argument-dependent name lookup
  struct any { template <class T> any(T const&); };
  
  // when operator BOOST_TT_TRAIT_OP is not available, this one is used
  no_operator operator BOOST_TT_TRAIT_OP (const any&);
  
  
  // 3. checks if the operator returns void or not
  // conditions: Rhs!=void
  
  // we first redefine "operator," so that we have no compilation error if
  // operator BOOST_TT_TRAIT_OP returns void and we can use the return type of
  // (BOOST_TT_TRAIT_OP rhs, returns_void_t()) to deduce if
  // operator BOOST_TT_TRAIT_OP returns void or not:
  // - operator BOOST_TT_TRAIT_OP returns void   -> (BOOST_TT_TRAIT_OP rhs, returns_void_t()) returns returns_void_t
  // - operator BOOST_TT_TRAIT_OP returns !=void -> (BOOST_TT_TRAIT_OP rhs, returns_void_t()) returns int
  struct returns_void_t { };
  template <typename T> int operator,(const T&, returns_void_t);
  template <typename T> int operator,(const volatile T&, returns_void_t);
  
  // this intermediate trait has member value of type bool:
  // - value==true -> operator BOOST_TT_TRAIT_OP returns void
  // - value==false -> operator BOOST_TT_TRAIT_OP does not return void
  template < typename Rhs >
  struct operator_returns_void {
     // overloads of function returns_void make the difference
     // yes_type and no_type have different size by construction
     static ::boost::type_traits::yes_type returns_void(returns_void_t);
     static ::boost::type_traits::no_type returns_void(int);
     BOOST_STATIC_CONSTANT(bool, value = (sizeof(::boost::type_traits::yes_type)==sizeof(returns_void((BOOST_TT_TRAIT_OP make<Rhs>(),returns_void_t())))));
  };
  
  
  // 4. checks if the return type is Ret or Ret==dont_care
  // conditions: Rhs!=void
  
  struct dont_care { };
  
  template < typename Rhs, typename Ret, bool Returns_void >
  struct operator_returns_Ret;
  
  template < typename Rhs >
  struct operator_returns_Ret < Rhs, dont_care, true > {
     BOOST_STATIC_CONSTANT(bool, value = true);
  };
  
  template < typename Rhs >
  struct operator_returns_Ret < Rhs, dont_care, false > {
     BOOST_STATIC_CONSTANT(bool, value = true);
  };
  
  template < typename Rhs >
  struct operator_returns_Ret < Rhs, void, true > {
     BOOST_STATIC_CONSTANT(bool, value = true);
  };
  
  template < typename Rhs >
  struct operator_returns_Ret < Rhs, void, false > {
     BOOST_STATIC_CONSTANT(bool, value = false);
  };
  
  template < typename Rhs, typename Ret >
  struct operator_returns_Ret < Rhs, Ret, true > {
     BOOST_STATIC_CONSTANT(bool, value = false);
  };
  
  // otherwise checks if it is convertible to Ret using the sizeof trick
  // based on overload resolution
  // condition: Ret!=void and Ret!=dont_care and the operator does not return void
  template < typename Rhs, typename Ret >
  struct operator_returns_Ret < Rhs, Ret, false > {
     static ::boost::type_traits::yes_type is_convertible_to_Ret(Ret); // this version is preferred for types convertible to Ret
     static ::boost::type_traits::no_type is_convertible_to_Ret(...); // this version is used otherwise
  
     BOOST_STATIC_CONSTANT(bool, value = (sizeof(is_convertible_to_Ret(BOOST_TT_TRAIT_OP make<Rhs>()))==sizeof(::boost::type_traits::yes_type)));
  };
  
  
  // 5. checks for operator existence
  // condition: Rhs!=void
  
  // checks if our definition of operator BOOST_TT_TRAIT_OP is used or an other
  // existing one;
  // this is done with redefinition of "operator," that returns no_operator or has_operator
  struct has_operator { };
  no_operator operator,(no_operator, has_operator);
  
  template < typename Rhs >
  struct operator_exists {
     static ::boost::type_traits::yes_type s_check(has_operator); // this version is preferred when operator exists
     static ::boost::type_traits::no_type s_check(no_operator); // this version is used otherwise
  
     BOOST_STATIC_CONSTANT(bool, value = (sizeof(s_check(((BOOST_TT_TRAIT_OP make<Rhs>()),make<has_operator>())))==sizeof(::boost::type_traits::yes_type)));
  };
  
  
  // 6. main trait: to avoid any compilation error, this class behaves
  // differently when operator BOOST_TT_TRAIT_OP(Rhs) is forbidden by the
  // standard.
  // Forbidden_if is a bool that is:
  // - true when the operator BOOST_TT_TRAIT_OP(Rhs) is forbidden by the standard
  //   (would yield compilation error if used)
  // - false otherwise
  template < typename Rhs, typename Ret, bool Forbidden_if >
  struct trait_impl1;
  
  template < typename Rhs, typename Ret >
  struct trait_impl1 < Rhs, Ret, true > {
     BOOST_STATIC_CONSTANT(bool, value = false);
  };
  
  template < typename Rhs, typename Ret >
  struct trait_impl1 < Rhs, Ret, false > {
     BOOST_STATIC_CONSTANT(bool,
        value = (operator_exists < Rhs >::value && operator_returns_Ret < Rhs, Ret, operator_returns_void < Rhs >::value >::value));
  };
  
  // specialization needs to be declared for the special void case
  template < typename Ret >
  struct trait_impl1 < void, Ret, false > {
     BOOST_STATIC_CONSTANT(bool, value = false);
  };
  
  // defines some typedef for convenience
  template < typename Rhs, typename Ret >
  struct trait_impl {
     typedef typename ::boost::remove_reference<Rhs>::type Rhs_noref;
     typedef typename ::boost::remove_cv<Rhs_noref>::type Rhs_nocv;
     typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Rhs_noref>::type >::type >::type Rhs_noptr;
     BOOST_STATIC_CONSTANT(bool, value = (trait_impl1 < Rhs_noref, Ret, BOOST_TT_FORBIDDEN_IF >::value));
  };
  
  } // namespace impl
  } // namespace detail
  
  // this is the accessible definition of the trait to end user
  template <class Rhs, class Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care>
  struct BOOST_TT_TRAIT_NAME : public integral_constant<bool, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _impl)::trait_impl < Rhs, Ret >::value)>{};
  
  } // namespace boost
  
  #if defined(BOOST_MSVC)
  #   pragma warning ( pop )
  #endif
  
  #endif
  
  