Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

boost/proto/generate.hpp

#ifndef BOOST_PP_IS_ITERATING
    ///////////////////////////////////////////////////////////////////////////////
    /// \file generate.hpp
    /// Contains definition of generate\<\> class template, which end users can
    /// specialize for generating domain-specific expression wrappers.
    //
    //  Copyright 2008 Eric Niebler. Distributed under 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)

    #ifndef BOOST_PROTO_GENERATE_HPP_EAN_02_13_2007
    #define BOOST_PROTO_GENERATE_HPP_EAN_02_13_2007

    #include <boost/config.hpp>
    #include <boost/preprocessor/cat.hpp>
    #include <boost/preprocessor/iteration/iterate.hpp>
    #include <boost/preprocessor/facilities/intercept.hpp>
    #include <boost/preprocessor/repetition/enum_params.hpp>
    #include <boost/preprocessor/repetition/enum_binary_params.hpp>
    #include <boost/preprocessor/repetition/enum_trailing_params.hpp>
    #include <boost/mpl/bool.hpp>
    #include <boost/utility/enable_if.hpp>
    #include <boost/utility/result_of.hpp>
    #include <boost/proto/proto_fwd.hpp>
    #include <boost/proto/args.hpp>

    namespace boost { namespace proto
    {

        namespace detail
        {
            template<typename Expr>
            struct by_value_generator_;

            template<typename Tag, typename Arg>
            struct by_value_generator_<proto::expr<Tag, term<Arg>, 0> >
            {
                typedef
                    proto::expr<
                        Tag
                      , term<typename detail::term_traits<Arg>::value_type>
                      , 0
                    >
                type;

                static type const call(proto::expr<Tag, term<Arg>, 0> const &e)
                {
                    type that = {e.child0};
                    return that;
                }
            };

            template<typename Tag, typename Arg>
            struct by_value_generator_<proto::basic_expr<Tag, term<Arg>, 0> >
            {
                typedef
                    proto::basic_expr<
                        Tag
                      , term<typename detail::term_traits<Arg>::value_type>
                      , 0
                    >
                type;

                static type const call(proto::basic_expr<Tag, term<Arg>, 0> const &e)
                {
                    type that = {e.child0};
                    return that;
                }
            };

        #define BOOST_PP_ITERATION_PARAMS_1 (3, (1, BOOST_PROTO_MAX_ARITY, <boost/proto/generate.hpp>))
        #include BOOST_PP_ITERATE()

        #undef BOOST_PROTO_DEFINE_BY_VALUE
        #undef BOOST_PROTO_DEFINE_BY_VALUE_TYPE

        }

        /// \brief A simple generator that passes an expression
        /// through unchanged.
        ///
        /// Generators are intended for use as the first template parameter
        /// to the \c domain\<\> class template and control if and how
        /// expressions within that domain are to be customized.
        /// The \c default_generator makes no modifications to the expressions
        /// passed to it.
        struct default_generator
        {
            BOOST_PROTO_CALLABLE()

            template<typename Sig>
            struct result;

            template<typename This, typename Expr>
            struct result<This(Expr)>
            {
                typedef Expr type;
            };

            /// \param expr A Proto expression
            /// \return expr
            template<typename Expr>
            #ifdef BOOST_PROTO_STRICT_RESULT_OF
            Expr
            #else
            Expr const &
            #endif
            operator ()(Expr const &e) const
            {
                return e;
            }
        };

        /// \brief A generator that wraps expressions passed
        /// to it in the specified extension wrapper.
        ///
        /// Generators are intended for use as the first template parameter
        /// to the \c domain\<\> class template and control if and how
        /// expressions within that domain are to be customized.
        /// \c generator\<\> wraps each expression passed to it in
        /// the \c Extends\<\> wrapper.
        template<template<typename> class Extends>
        struct generator
        {
            BOOST_PROTO_CALLABLE()
            BOOST_PROTO_USE_BASIC_EXPR()

            template<typename Sig>
            struct result;

            template<typename This, typename Expr>
            struct result<This(Expr)>
            {
                typedef Extends<Expr> type;
            };

            template<typename This, typename Expr>
            struct result<This(Expr &)>
            {
                typedef Extends<Expr> type;
            };

            template<typename This, typename Expr>
            struct result<This(Expr const &)>
            {
                typedef Extends<Expr> type;
            };

            /// \param expr A Proto expression
            /// \return Extends<Expr>(expr)
            template<typename Expr>
            Extends<Expr> operator ()(Expr const &e) const
            {
                return Extends<Expr>(e);
            }
        };

        /// \brief A generator that wraps expressions passed
        /// to it in the specified extension wrapper and uses
        /// aggregate initialization for the wrapper.
        ///
        /// Generators are intended for use as the first template parameter
        /// to the \c domain\<\> class template and control if and how
        /// expressions within that domain are to be customized.
        /// \c pod_generator\<\> wraps each expression passed to it in
        /// the \c Extends\<\> wrapper, and uses aggregate initialzation
        /// for the wrapped object.
        template<template<typename> class Extends>
        struct pod_generator
        {
            BOOST_PROTO_CALLABLE()
            BOOST_PROTO_USE_BASIC_EXPR()

            template<typename Sig>
            struct result;

            template<typename This, typename Expr>
            struct result<This(Expr)>
            {
                typedef Extends<Expr> type;
            };

            template<typename This, typename Expr>
            struct result<This(Expr &)>
            {
                typedef Extends<Expr> type;
            };

            template<typename This, typename Expr>
            struct result<This(Expr const &)>
            {
                typedef Extends<Expr> type;
            };

            /// \param expr The expression to wrap
            /// \return <tt>Extends\<Expr\> that = {expr}; return that;</tt>
            template<typename Expr>
            Extends<Expr> operator ()(Expr const &e) const
            {
                Extends<Expr> that = {e};
                return that;
            }
        };

        /// \brief A generator that replaces child nodes held by
        /// reference with ones held by value. Use with
        /// \c compose_generators to forward that result to another
        /// generator.
        ///
        /// Generators are intended for use as the first template parameter
        /// to the \c domain\<\> class template and control if and how
        /// expressions within that domain are to be customized.
        /// \c by_value_generator ensures all child nodes are
        /// held by value. This generator is typically composed with a
        /// second generator for further processing, as
        /// <tt>compose_generators\<by_value_generator, MyGenerator\></tt>.
        struct by_value_generator
        {
            BOOST_PROTO_CALLABLE()

            template<typename Sig>
            struct result;

            template<typename This, typename Expr>
            struct result<This(Expr)>
            {
                typedef
                    typename detail::by_value_generator_<Expr>::type
                type;
            };

            template<typename This, typename Expr>
            struct result<This(Expr &)>
            {
                typedef
                    typename detail::by_value_generator_<Expr>::type
                type;
            };

            template<typename This, typename Expr>
            struct result<This(Expr const &)>
            {
                typedef
                    typename detail::by_value_generator_<Expr>::type
                type;
            };

            /// \param expr The expression to modify.
            /// \return <tt>deep_copy(expr)</tt>
            template<typename Expr>
            typename result<by_value_generator(Expr)>::type operator ()(Expr const &e) const
            {
                return detail::by_value_generator_<Expr>::call(e);
            }
        };

        /// \brief A composite generator that first applies one
        /// transform to an expression and then forwards the result
        /// on to another generator for further transformation.
        ///
        /// Generators are intended for use as the first template parameter
        /// to the \c domain\<\> class template and control if and how
        /// expressions within that domain are to be customized.
        /// \c compose_generators\<\> is a composite generator that first
        /// applies one transform to an expression and then forwards the
        /// result on to another generator for further transformation.
        template<typename First, typename Second>
        struct compose_generators
        {
            BOOST_PROTO_CALLABLE()

            template<typename Sig>
            struct result;

            template<typename This, typename Expr>
            struct result<This(Expr)>
            {
                typedef
                    typename Second::template result<
                        Second(typename First::template result<First(Expr)>::type)
                    >::type
                type;
            };

            template<typename This, typename Expr>
            struct result<This(Expr &)>
            {
                typedef
                    typename Second::template result<
                        Second(typename First::template result<First(Expr)>::type)
                    >::type
                type;
            };

            template<typename This, typename Expr>
            struct result<This(Expr const &)>
            {
                typedef
                    typename Second::template result<
                        Second(typename First::template result<First(Expr)>::type)
                    >::type
                type;
            };

            /// \param expr The expression to modify.
            /// \return Second()(First()(expr))
            template<typename Expr>
            typename result<compose_generators(Expr)>::type operator ()(Expr const &e) const
            {
                return Second()(First()(e));
            }
        };

        /// \brief Annotate a generator to indicate that it would
        /// prefer to be passed instances of \c proto::basic_expr\<\> rather
        /// than \c proto::expr\<\>. <tt>use_basic_expr\<Generator\></tt> is
        /// itself a generator.
        ///
        template<typename Generator>
        struct use_basic_expr
          : Generator
        {
            BOOST_PROTO_USE_BASIC_EXPR()
        };

        /// \brief Tests a generator to see whether it would prefer
        /// to be passed instances of \c proto::basic_expr\<\> rather than
        /// \c proto::expr\<\>.
        ///
        template<typename Generator, typename Void>
        struct wants_basic_expr
          : mpl::false_
        {};

        template<typename Generator>
        struct wants_basic_expr<Generator, typename Generator::proto_use_basic_expr_>
          : mpl::true_
        {};

        /// INTERNAL ONLY
        template<>
        struct is_callable<default_generator>
          : mpl::true_
        {};

        /// INTERNAL ONLY
        template<template<typename> class Extends>
        struct is_callable<generator<Extends> >
          : mpl::true_
        {};

        /// INTERNAL ONLY
        template<template<typename> class Extends>
        struct is_callable<pod_generator<Extends> >
          : mpl::true_
        {};

        /// INTERNAL ONLY
        template<>
        struct is_callable<by_value_generator>
          : mpl::true_
        {};

        /// INTERNAL ONLY
        template<typename First, typename Second>
        struct is_callable<compose_generators<First, Second> >
          : mpl::true_
        {};

    }}

    // Specialization of boost::result_of to eliminate some unnecessary template instantiations
    namespace boost
    {
        template<typename Expr>
        struct result_of<proto::default_domain(Expr)>
        {
            typedef Expr type;
        };

        template<typename Expr>
        struct result_of<proto::default_generator(Expr)>
        {
            typedef Expr type;
        };
    }

    #endif // BOOST_PROTO_GENERATE_HPP_EAN_02_13_2007

#else // BOOST_PP_IS_ITERATING

    #define N BOOST_PP_ITERATION()

            template<typename Tag BOOST_PP_ENUM_TRAILING_PARAMS(N, typename Arg) >
            struct by_value_generator_<
                proto::expr<Tag, BOOST_PP_CAT(list, N)<BOOST_PP_ENUM_PARAMS(N, Arg)>, N>
            >
            {
                typedef
                    BOOST_PP_CAT(list, N)<BOOST_PP_ENUM_PARAMS(N, Arg)>
                src_args;

                typedef
                    BOOST_PP_CAT(list, N)<
                        BOOST_PP_ENUM_BINARY_PARAMS(N, typename uncvref<Arg, >::type BOOST_PP_INTERCEPT)
                    >
                dst_args;

                typedef proto::expr<Tag, src_args, N> src_type;
                typedef proto::expr<Tag, dst_args, N> type;

                static type const call(src_type const &e)
                {
                    type that = {
                        BOOST_PP_ENUM_PARAMS(N, e.child)
                    };
                    return that;
                }
            };

            template<typename Tag BOOST_PP_ENUM_TRAILING_PARAMS(N, typename Arg) >
            struct by_value_generator_<
                proto::basic_expr<Tag, BOOST_PP_CAT(list, N)<BOOST_PP_ENUM_PARAMS(N, Arg)>, N>
            >
            {
                typedef
                    BOOST_PP_CAT(list, N)<BOOST_PP_ENUM_PARAMS(N, Arg)>
                src_args;

                typedef
                    BOOST_PP_CAT(list, N)<
                        BOOST_PP_ENUM_BINARY_PARAMS(N, typename uncvref<Arg, >::type BOOST_PP_INTERCEPT)
                    >
                dst_args;

                typedef proto::basic_expr<Tag, src_args, N> src_type;
                typedef proto::basic_expr<Tag, dst_args, N> type;

                static type const call(src_type const &e)
                {
                    type that = {
                        BOOST_PP_ENUM_PARAMS(N, e.child)
                    };
                    return that;
                }
            };

    #undef N

#endif