make.hpp

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            struct make : proto::callable
            {
                template<typename Sig>
                struct result;

                template<typename This, typename Expr, typename State, typename Visitor>
                struct result<This(Expr, State, Visitor)>
                {
                    typedef typename detail::make_if_<Object, Expr, State, Visitor>::type type;
                };

                /// \param expr The current expression
                /// \param state The current state
                /// \param visitor An arbitrary visitor
                /// \return <tt>result\<void(Expr, State, Visitor)\>::::type()</tt>
                template<typename Expr, typename State, typename Visitor>
                typename result<void(Expr, State, Visitor)>::type
                operator ()(Expr const &, State const &, Visitor &) const
                {
                    typedef typename result<void(Expr, State, Visitor)>::type result_type;
                    return result_type();
                }
            };

            #define BOOST_PP_ITERATION_PARAMS_1 (3, (0, BOOST_PROTO_MAX_ARITY, <boost/xpressive/proto/transform/make.hpp>))
            #include BOOST_PP_ITERATE()
        }

        /// INTERNAL ONLY
        ///
        template<typename Object>
        struct is_callable<transform::make<Object> >
          : mpl::true_
        {};

    }}

    #endif

#else

    #define N BOOST_PP_ITERATION()

        namespace detail
        {
            #if N > 0
            template<typename T BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)>
            struct nested_type_if<
                T
              , typelist<BOOST_PP_ENUM_PARAMS(N, A)>
              , typename typelist<
                    BOOST_PP_ENUM_BINARY_PARAMS(N, typename A, ::not_applied_ BOOST_PP_INTERCEPT)
                >::type
            >
            {
                typedef T type;
                typedef void not_applied_;
            };

            template<
                template<BOOST_PP_ENUM_PARAMS(N, typename BOOST_PP_INTERCEPT)> class R
                BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)
              , typename Expr, typename State, typename Visitor
            >
            struct make_<R<BOOST_PP_ENUM_PARAMS(N, A)>, Expr, State, Visitor
                BOOST_MPL_AUX_LAMBDA_ARITY_PARAM(N)
            >
              : nested_type_if<
                    #define TMP0(Z, M, DATA) make_if_<BOOST_PP_CAT(A, M), Expr, State, Visitor>
                    #define TMP1(Z, M, DATA) typename TMP0(Z, M, DATA) ::type
                    R<BOOST_PP_ENUM(N, TMP1, ~)>
                  , typelist<BOOST_PP_ENUM(N, TMP0, ~) >
                    #undef TMP0
                    #undef TMP1
                >
            {};
            #endif

            template<
                typename R
                BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)
              , typename Expr, typename State, typename Visitor
            >
            struct make_if_<R(BOOST_PP_ENUM_PARAMS(N, A)), Expr, State, Visitor, false>
            {
                typedef typename when<_, R(BOOST_PP_ENUM_PARAMS(N, A))>::template result<void(Expr, State, Visitor)>::type type;
            };

            template<
                typename R
                BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)
              , typename Expr, typename State, typename Visitor
            >
            struct make_if_<R(*)(BOOST_PP_ENUM_PARAMS(N, A)), Expr, State, Visitor, false>
            {
                typedef typename when<_, R(BOOST_PP_ENUM_PARAMS(N, A))>::template result<void(Expr, State, Visitor)>::type type;
            };

            template<typename T, typename A>
            struct construct_<proto::expr<T, A, N>, true>
            {
                typedef proto::expr<T, A, N> result_type;

                template<BOOST_PP_ENUM_PARAMS(BOOST_PP_MAX(N, 1), typename A)>
                result_type operator ()(BOOST_PP_ENUM_BINARY_PARAMS(BOOST_PP_MAX(N, 1), A, &a)) const
                {
                    return result_type::make(BOOST_PP_ENUM_PARAMS(BOOST_PP_MAX(N, 1), a));
                }
            };
        }

        /// \brief A PrimitiveTransform which computes a type by evaluating any
        /// nested transforms and then constructs an object of that type with the
        /// current expression, state and visitor, transformed according
        /// to \c A0 through \c AN.
        template<typename Object BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)>
        struct make<Object(BOOST_PP_ENUM_PARAMS(N, A))> : proto::callable
        {
            template<typename Sig>
            struct result;

            template<typename This, typename Expr, typename State, typename Visitor>
            struct result<This(Expr, State, Visitor)>
            {
                /// \brief <tt>make\<Object\>::::result\<void(Expr, State, Visitor)\>::::type</tt>
                typedef typename detail::make_if_<Object, Expr, State, Visitor>::type type;
            };

            /// Let \c ax be <tt>when\<_, Ax\>()(expr, state, visitor)</tt>
            /// for each \c x in <tt>[0,N]</tt>.
            /// Let \c T be <tt>result\<void(Expr, State, Visitor)\>::::type</tt>.
            /// Return <tt>T(a0, a1,... aN)</tt>.
            ///
            /// \param expr The current expression
            /// \param state The current state
            /// \param visitor An arbitrary visitor
            template<typename Expr, typename State, typename Visitor>
            typename result<void(Expr, State, Visitor)>::type
            operator ()(Expr const &expr, State const &state, Visitor &visitor) const
            {
                typedef typename result<void(Expr, State, Visitor)>::type result_type;
                proto::detail::ignore_unused(expr);
                proto::detail::ignore_unused(state);
                proto::detail::ignore_unused(visitor);
                return detail::construct<result_type>(
                    #define TMP(Z, M, DATA) detail::as_lvalue(when<_, BOOST_PP_CAT(A, M)>()(expr, state, visitor))
                    BOOST_PP_ENUM(N, TMP, DATA)
                    #undef TMP
                );
            }
        };

        #if BOOST_WORKAROUND(__GNUC__, == 3)
        // work around GCC bug
        template<typename Tag, typename Args, long Arity BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)>
        struct make<proto::expr<Tag, Args, Arity>(BOOST_PP_ENUM_PARAMS(N, A))>
          : proto::callable
        {
            template<typename Sig>
            struct result;

            template<typename This, typename Expr, typename State, typename Visitor>
            struct result<This(Expr, State, Visitor)>
            {
                typedef proto::expr<Tag, Args, Arity> type;
            };

            template<typename Expr, typename State, typename Visitor>
            proto::expr<Tag, Args, Arity> operator ()(Expr const &expr, State const &state, Visitor &visitor) const
            {
                return proto::expr<Tag, Args, Arity>::make(
                    #define TMP(Z, M, DATA) detail::as_lvalue(when<_, BOOST_PP_CAT(A, M)>()(expr, state, visitor))
                    BOOST_PP_ENUM(N, TMP, DATA)
                    #undef TMP
                );
            }
        };
        #endif

    #undef N

#endif