traits.hpp

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#ifndef BOOST_PP_IS_ITERATING
    ///////////////////////////////////////////////////////////////////////////////
    /// \file traits.hpp
    /// Contains definitions for arg\<\>, arg_c\<\>, left\<\>,
    /// right\<\>, tag_of\<\>, and the helper functions arg(), arg_c(),
    /// left() and right().
    //
    //  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_ARG_TRAITS_HPP_EAN_04_01_2005
    #define BOOST_PROTO_ARG_TRAITS_HPP_EAN_04_01_2005

    #include <boost/xpressive/proto/detail/prefix.hpp>
    #include <boost/config.hpp>
    #include <boost/detail/workaround.hpp>
    #include <boost/preprocessor/iteration/iterate.hpp>
    #include <boost/preprocessor/repetition/enum.hpp>
    #include <boost/preprocessor/repetition/enum_params.hpp>
    #include <boost/preprocessor/repetition/enum_trailing.hpp>
    #include <boost/preprocessor/repetition/enum_trailing_params.hpp>
    #include <boost/preprocessor/repetition/repeat.hpp>
    #include <boost/preprocessor/repetition/repeat_from_to.hpp>
    #include <boost/preprocessor/facilities/intercept.hpp>
    #include <boost/preprocessor/arithmetic/sub.hpp>
    #include <boost/ref.hpp>
    #include <boost/mpl/if.hpp>
    #include <boost/mpl/or.hpp>
    #include <boost/mpl/bool.hpp>
    #include <boost/mpl/eval_if.hpp>
    #include <boost/mpl/aux_/template_arity.hpp>
    #include <boost/mpl/aux_/lambda_arity_param.hpp>
    #include <boost/static_assert.hpp>
    #include <boost/utility/result_of.hpp>
    #include <boost/type_traits/is_pod.hpp>
    #include <boost/type_traits/is_same.hpp>
    #include <boost/type_traits/is_array.hpp>
    #include <boost/type_traits/is_function.hpp>
    #include <boost/type_traits/remove_cv.hpp>
    #include <boost/type_traits/remove_const.hpp>
    #include <boost/type_traits/add_reference.hpp>
    #include <boost/xpressive/proto/proto_fwd.hpp>
    #include <boost/xpressive/proto/ref.hpp>
    #include <boost/xpressive/proto/args.hpp>
    #include <boost/xpressive/proto/tags.hpp>
    #include <boost/xpressive/proto/transform/pass_through.hpp>
    #include <boost/xpressive/proto/detail/suffix.hpp>

    #if BOOST_WORKAROUND( BOOST_MSVC, == 1310 )
        #define BOOST_PROTO_IS_ARRAY_(T) boost::is_array<typename boost::remove_const<T>::type>
    #else
        #define BOOST_PROTO_IS_ARRAY_(T) boost::is_array<T>
    #endif

    #if BOOST_WORKAROUND( BOOST_MSVC, >= 1400 )
        #pragma warning(push)
        #pragma warning(disable: 4180) // warning C4180: qualifier applied to function type has no meaning; ignored
    #endif

    namespace boost { namespace proto
    {
        namespace detail
        {
            template<typename T, typename Void = void>
            struct if_vararg
            {};

            template<typename T>
            struct if_vararg<T, typename T::proto_is_vararg_>
              : T
            {};

            template<typename T, typename Void = void>
            struct is_callable2_
              : mpl::false_
            {};

            template<typename T>
            struct is_callable2_<T, typename T::proto_is_callable_>
              : mpl::true_
            {};

            template<typename T BOOST_MPL_AUX_LAMBDA_ARITY_PARAM(long Arity = mpl::aux::template_arity<T>::value)>
            struct is_callable_
              : is_callable2_<T>
            {};
        }

        /// \brief Boolean metafunction which detects whether a type is
        /// a callable function object type or not.
        ///
        /// <tt>is_callable\<\></tt> is used by the <tt>when\<\></tt> transform
        /// to determine whether a function type <tt>R(A1,A2,...AN)</tt> is a
        /// callable transform or an object transform. (The former are evaluated
        /// using <tt>call\<\></tt> and the later with <tt>make\<\></tt>.) If
        /// <tt>is_callable\<R\>::::value</tt> is \c true, the function type is
        /// a callable transform; otherwise, it is an object transform.
        ///
        /// Unless specialized for a type \c T, <tt>is_callable\<T\>::::value</tt>
        /// is computed as follows:
        ///
        /// \li If \c T is a template type <tt>X\<Y0,Y1,...YN\></tt>, where all \c Yx
        /// are types for \c x in <tt>[0,N]</tt>, <tt>is_callable\<T\>::::value</tt>
        /// is <tt>is_same\<YN, proto::callable\>::::value</tt>.
        /// \li If \c T has a nested type \c proto_is_callable_ that is a typedef
        /// for \c void, <tt>is_callable\<T\>::::value</tt> is \c true. (Note: this is
        /// the case for any type that derives from \c proto::callable.)
        /// \li Otherwise, <tt>is_callable\<T\>::::value</tt> is \c false.
        template<typename T>
        struct is_callable
          : proto::detail::is_callable_<T>
        {};

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

        /// INTERNAL ONLY
        ///
        template<>
        struct is_callable<proto::callable>
          : mpl::false_
        {};

        #if BOOST_WORKAROUND(__GNUC__, == 3)
        // work around GCC bug
        template<typename Tag, typename Args, long N>
        struct is_callable<proto::expr<Tag, Args, N> >
          : mpl::false_
        {};
        #endif

        /// \brief A Boolean metafunction that indicates whether a type requires
        /// aggregate initialization.
        ///
        /// <tt>is_aggregate\<\></tt> is used by the <tt>make\<\></tt> transform
        /// to determine how to construct an object of some type \c T, given some
        /// initialization arguments <tt>a0,a1,...aN</tt>.
        /// If <tt>is_aggregate\<T\>::::value</tt> is \c true, then an object of
        /// type T will be initialized as <tt>T t = {a0,a1,...aN};</tt>. Otherwise,
        /// it will be initialized as <tt>T t(a0,a1,...aN)</tt>.
        template<typename T>
        struct is_aggregate
          : is_pod<T>
        {};

        /// \brief Specialization of <tt>is_aggregate\<\></tt> that indicates
        /// that objects of <tt>expr\<\></tt> type require aggregate initialization.
        template<typename Tag, typename Args, long N>
        struct is_aggregate<proto::expr<Tag, Args, N> >
          : mpl::true_
        {};

        namespace result_of
        {
            /// \brief A Boolean metafunction that indicates whether a given
            /// type \c T is a Proto expression type.
            ///
            /// If \c T has a nested type \c proto_is_expr_ that is a typedef
            /// for \c void, <tt>is_expr\<T\>::::value</tt> is \c true. (Note, this
            /// is the case for <tt>proto::expr\<\></tt>, any type that is derived
            /// from <tt>proto::extends\<\></tt> or that uses the
            /// <tt>BOOST_PROTO_EXTENDS()</tt> macro.) Otherwise,
            /// <tt>is_expr\<T\>::::value</tt> is \c false.
            template<typename T, typename Void  BOOST_PROTO_FOR_DOXYGEN_ONLY(= void)>
            struct is_expr
              : mpl::false_
            {};

            /// \brief A Boolean metafunction that indicates whether a given
            /// type \c T is a Proto expression type.
            ///
            /// If \c T has a nested type \c proto_is_expr_ that is a typedef
            /// for \c void, <tt>is_expr\<T\>::::value</tt> is \c true. (Note, this
            /// is the case for <tt>proto::expr\<\></tt>, any type that is derived
            /// from <tt>proto::extends\<\></tt> or that uses the
            /// <tt>BOOST_PROTO_EXTENDS()</tt> macro.) Otherwise,
            /// <tt>is_expr\<T\>::::value</tt> is \c false.
            template<typename T>
            struct is_expr<T, typename T::proto_is_expr_>
              : mpl::true_
            {};

            /// \brief A metafunction that returns the tag type of a
            /// Proto expression.
            template<typename Expr>
            struct tag_of
            {
                typedef typename Expr::proto_tag type;
            };

            /// INTERNAL ONLY
            ///
            template<typename T, typename Void  BOOST_PROTO_FOR_DOXYGEN_ONLY(= void)>
            struct is_ref
              : mpl::false_
            {};

            /// INTERNAL ONLY
            ///
            template<typename T>
            struct is_ref<T, typename T::proto_is_ref_>
              : mpl::true_
            {};

            /// \brief A metafunction that computes the return type of the \c as_expr()
            /// function.
            ///
            /// The <tt>as_expr\<\></tt> metafunction turns types into Proto types, if
            /// they are not already, by making them Proto terminals held by value if
            /// possible. Types which are already Proto types are left alone.
            ///
            /// This specialization is selected when the type is not yet a Proto type.
            /// The resulting terminal type is calculated as follows:
            ///
            /// If \c T is an array type or a function type, let \c A be <tt>T &</tt>.
            /// Otherwise, let \c A be the type \c T stripped of cv-qualifiers.
            /// Then, the result type <tt>as_expr\<T, Domain\>::::type</tt> is
            /// <tt>Domain::apply\< expr\< tag::terminal, args0\<A\> \> \>::::type</tt>.
            template<
                typename T
              , typename Domain BOOST_PROTO_FOR_DOXYGEN_ONLY(= default_domain)
              , typename Void   BOOST_PROTO_FOR_DOXYGEN_ONLY(= void)
            >
            struct as_expr
            {
                typedef mpl::or_<BOOST_PROTO_IS_ARRAY_(T), is_function<T> > is_unstorable_;
                typedef typename mpl::eval_if<is_unstorable_, add_reference<T>, remove_cv<T> >::type arg0_;
                typedef proto::expr<proto::tag::terminal, args0<arg0_> > expr_;
                typedef typename Domain::template apply<expr_>::type type;
                typedef type const reference;

                /// INTERNAL ONLY
                ///
                template<typename T2>
                static reference call(T2 &t)
                {
                    return Domain::make(expr_::make(t));
                }
            };

            /// \brief A metafunction that computes the return type of the \c as_expr()
            /// function.
            ///
            /// The <tt>as_expr\<\></tt> metafunction turns types into Proto types, if
            /// they are not already, by making them Proto terminals held by value if
            /// possible. Types which are already Proto types are left alone.
            ///
            /// This specialization is selected when the type is already a Proto type.
            /// The result type <tt>as_expr\<T, Domain\>::::type</tt> is \c T stripped
            /// of cv-qualifiers.
            template<typename T, typename Domain>
            struct as_expr<T, Domain, typename T::proto_is_expr_>
            {
                typedef typename T::proto_derived_expr type;
                typedef T &reference;

                /// INTERNAL ONLY
                ///
                template<typename T2>
                static reference call(T2 &t)
                {
                    return t;
                }
            };

            /// \brief A metafunction that computes the return type of the \c as_arg()
            /// function.
            ///
            /// The <tt>as_arg\<\></tt> metafunction turns types into Proto types, if
            /// they are not already, by making them Proto terminals held by reference.
            /// Types which are already Proto types are wrapped in <tt>proto::ref_\<\></tt>.
            ///
            /// This specialization is selected when the type is not yet a Proto type.
            /// The result type <tt>as_arg\<T, Domain\>::::type</tt> is
            /// <tt>Domain::apply\< expr\< tag::terminal, args0\<T &\> \> \>::::type</tt>.
            template<
                typename T
              , typename Domain BOOST_PROTO_FOR_DOXYGEN_ONLY(= default_domain)
              , typename Void   BOOST_PROTO_FOR_DOXYGEN_ONLY(= void)
            >
            struct as_arg
            {
                typedef proto::expr<proto::tag::terminal, args0<T &> > expr_;
                typedef typename Domain::template apply<expr_>::type type;

                /// INTERNAL ONLY
                ///
                template<typename T2>
                static type call(T2 &t)
                {
                    return Domain::make(expr_::make(t));
                }
            };

            /// \brief A metafunction that computes the return type of the \c as_arg()
            /// function.
            ///