Boost C++ Libraries

boost/spirit/home/support/auto/meta_create.hpp

//  Copyright (c) 2001-2011 Hartmut Kaiser
//
//  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)

#if !defined(BOOST_SPIRIT_SUPPORT_META_CREATE_NOV_21_2009_0327PM)
#define BOOST_SPIRIT_SUPPORT_META_CREATE_NOV_21_2009_0327PM

#if defined(_MSC_VER)
#pragma once
#endif

#include <boost/spirit/home/support/unused.hpp>

#include <boost/version.hpp>
#include <boost/proto/make_expr.hpp>
#include <boost/proto/traits.hpp>
#include <boost/utility/result_of.hpp>
#include <boost/type_traits/add_const.hpp>
#include <boost/type_traits/add_reference.hpp>
#include <boost/type_traits/remove_const.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <boost/fusion/include/fold.hpp>
#include <boost/mpl/and.hpp>
#include <boost/mpl/not.hpp>

// needed for workaround below
#if defined(__GNUC__) && ((__GNUC__ < 4) || (__GNUC__ == 4) && (__GNUC_MINOR__ < 3))
#include <boost/type_traits/is_same.hpp>
#endif

namespace boost { namespace spirit { namespace traits
{
    ///////////////////////////////////////////////////////////////////////////
    // This is the main dispatch point for meta_create to the correct domain
    template <typename Domain, typename T, typename Enable = void>
    struct meta_create;

    ///////////////////////////////////////////////////////////////////////////
    // This allows to query whether a valid mapping exists for the given data 
    // type to a component in the given domain
    template <typename Domain, typename T, typename Enable = void>
    struct meta_create_exists : mpl::false_ {};
}}}

namespace boost { namespace spirit 
{
    ///////////////////////////////////////////////////////////////////////////
    namespace detail
    {
        template <typename T>
        struct add_const_ref
          : add_reference<typename add_const<T>::type> {};

        template <typename T>
        struct remove_const_ref
          : remove_const<typename remove_reference<T>::type> {};

// starting with Boost V1.42 fusion::fold has been changed to be compatible 
// with mpl::fold (the sequence of template parameters for the meta-function 
// object has been changed)
#if BOOST_VERSION < 104200
        ///////////////////////////////////////////////////////////////////////
        template <typename OpTag, typename Domain>
        struct nary_proto_expr_function
        {
            template <typename T>
            struct result;

// this is a workaround for older versions of g++ (< V4.3) which apparently have
// problems with the following template specialization
#if defined(__GNUC__) && ((__GNUC__ < 4) || (__GNUC__ == 4) && (__GNUC_MINOR__ < 3))
            template <typename F, typename T1, typename T2>
            struct result<F(T1, T2)>
            {
                BOOST_STATIC_ASSERT((is_same<F, nary_proto_expr_function>::value));
#else
            template <typename T1, typename T2>
            struct result<nary_proto_expr_function(T1, T2)>
            {
#endif
                typedef typename remove_const_ref<T2>::type left_type;
                typedef typename 
                    spirit::traits::meta_create<Domain, T1>::type
                right_type;

                typedef typename mpl::eval_if<
                    traits::not_is_unused<left_type>
                  , proto::result_of::make_expr<OpTag, left_type, right_type>
                  , mpl::identity<right_type>
                >::type type;
            };

            template <typename T>
            typename result<nary_proto_expr_function(T, unused_type const&)>::type
            operator()(T, unused_type const&) const
            {
                typedef spirit::traits::meta_create<Domain, T> right_type;
                return right_type::call();
            }

            template <typename T1, typename T2>
            typename result<nary_proto_expr_function(T1, T2)>::type
            operator()(T1, T2 const& t2) const
            {
                // we variants to the alternative operator
                typedef spirit::traits::meta_create<Domain, T1> right_type;
                return proto::make_expr<OpTag>(t2, right_type::call());
            }
        };
#else
        ///////////////////////////////////////////////////////////////////////
        template <typename OpTag, typename Domain>
        struct nary_proto_expr_function
        {
            template <typename T>
            struct result;

// this is a workaround for older versions of g++ (< V4.3) which apparently have
// problems with the following template specialization
#if defined(__GNUC__) && ((__GNUC__ < 4) || (__GNUC__ == 4) && (__GNUC_MINOR__ < 3))
            template <typename F, typename T1, typename T2>
            struct result<F(T1, T2)>
            {
                BOOST_STATIC_ASSERT((is_same<F, nary_proto_expr_function>::value));
#else
            template <typename T1, typename T2>
            struct result<nary_proto_expr_function(T1, T2)>
            {
#endif
                typedef typename remove_const_ref<T1>::type left_type;
                typedef typename 
                    spirit::traits::meta_create<Domain, T2>::type
                right_type;

                typedef typename mpl::eval_if<
                    traits::not_is_unused<left_type>
                  , proto::result_of::make_expr<OpTag, left_type, right_type>
                  , mpl::identity<right_type>
                >::type type;
            };

            template <typename T>
            typename result<nary_proto_expr_function(unused_type const&, T)>::type
            operator()(unused_type const&, T) const
            {
                typedef spirit::traits::meta_create<Domain, T> right_type;
                return right_type::call();
            }

            template <typename T1, typename T2>
            typename result<nary_proto_expr_function(T1, T2)>::type
            operator()(T1 const& t1, T2) const
            {
                // we variants to the alternative operator
                typedef spirit::traits::meta_create<Domain, T2> right_type;
                return proto::make_expr<OpTag>(t1, right_type::call());
            }
        };
#endif
    }

    ///////////////////////////////////////////////////////////////////////
    template <typename T, typename OpTag, typename Domain>
    struct make_unary_proto_expr
    {
        typedef spirit::traits::meta_create<Domain, T> subject_type;

        typedef typename proto::result_of::make_expr<
            OpTag, typename subject_type::type
        >::type type;

        static type call()
        {
            return proto::make_expr<OpTag>(subject_type::call());
        }
    };

    ///////////////////////////////////////////////////////////////////////////
    template <typename Sequence, typename OpTag, typename Domain>
    struct make_nary_proto_expr
    {
        typedef detail::nary_proto_expr_function<OpTag, Domain> 
            make_proto_expr;

        typedef typename fusion::result_of::fold<
            Sequence, unused_type, make_proto_expr
        >::type type;

        static type call()
        {
            return fusion::fold(Sequence(), unused, make_proto_expr());
        }
    };

    ///////////////////////////////////////////////////////////////////////////
    namespace detail
    {
        // Starting with newer versions of Proto, all Proto expressions are at 
        // the same time Fusion sequences. This is the correct behavior, but
        // we need to distinguish between Fusion sequences and Proto 
        // expressions. This meta-function does exactly that.
        template <typename T>
        struct is_fusion_sequence_but_not_proto_expr
          : mpl::and_<
                fusion::traits::is_sequence<T>
              , mpl::not_<proto::is_expr<T> > >
        {};
    }
}}

#endif