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0001 /*=============================================================================
0002     Copyright (c) 2001-2011 Hartmut Kaiser
0003 
0004     Distributed under the Boost Software License, Version 1.0. (See accompanying
0005     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 =============================================================================*/
0007 #ifndef BOOST_SPIRIT_QI_DETAIL_ALTERNATIVE_FUNCTION_HPP
0008 #define BOOST_SPIRIT_QI_DETAIL_ALTERNATIVE_FUNCTION_HPP
0009 
0010 #if defined(_MSC_VER)
0011 #pragma once
0012 #endif
0013 
0014 #include <boost/spirit/home/qi/domain.hpp>
0015 #include <boost/spirit/home/qi/detail/assign_to.hpp>
0016 #include <boost/spirit/home/support/unused.hpp>
0017 #include <boost/spirit/home/qi/detail/attributes.hpp>
0018 #include <boost/variant.hpp>
0019 #include <boost/mpl/bool.hpp>
0020 
0021 namespace boost { namespace spirit { namespace qi { namespace detail
0022 {
0023     template <typename Variant, typename T>
0024     struct find_substitute
0025     {
0026         // Get the type from the Variant that can be a substitute for T.
0027         // If none is found, just return T
0028 
0029         typedef Variant variant_type;
0030         typedef typename variant_type::types types;
0031         typedef typename mpl::end<types>::type end;
0032 
0033         typedef typename mpl::find<types, T>::type iter_1;
0034 
0035         typedef typename
0036             mpl::eval_if<
0037                 is_same<iter_1, end>,
0038                 mpl::find_if<types, traits::is_substitute<T, mpl::_1> >,
0039                 mpl::identity<iter_1>
0040             >::type
0041         iter;
0042 
0043         typedef typename
0044             mpl::eval_if<
0045                 is_same<iter, end>,
0046                 mpl::identity<T>,
0047                 mpl::deref<iter>
0048             >::type
0049         type;
0050     };
0051 
0052 #ifdef _MSC_VER
0053 #  pragma warning(push)
0054 #  pragma warning(disable: 4512) // assignment operator could not be generated.
0055 #endif
0056     template <typename Iterator, typename Context, typename Skipper,
0057         typename Attribute>
0058     struct alternative_function
0059     {
0060         alternative_function(
0061             Iterator& first_, Iterator const& last_, Context& context_,
0062             Skipper const& skipper_, Attribute& attr_)
0063           : first(first_), last(last_), context(context_), skipper(skipper_),
0064             attr(attr_)
0065         {
0066         }
0067 
0068         template <typename Component>
0069         bool call(Component const& component, mpl::true_) const
0070         {
0071             // if Attribute is not a variant, then pass it as-is
0072             return component.parse(first, last, context, skipper, attr);
0073         }
0074 
0075         template <typename Component>
0076         bool call_optional_or_variant(Component const& component, mpl::true_) const
0077         {
0078             // If Attribute is an optional, then create an attribute for the Component
0079             // with the type optional::value_type. If the expected attribute is unused type,
0080             // use it instead.
0081             typedef typename
0082                 traits::attribute_of<Component, Context, Iterator>::type
0083             expected_type;
0084 
0085             typename mpl::if_<
0086                 is_same<expected_type, unused_type>,
0087                 unused_type,
0088                 typename Attribute::value_type>::type
0089             val;
0090 
0091             if (component.parse(first, last, context, skipper, val))
0092             {
0093                 traits::assign_to(val, attr);
0094                 return true;
0095             }
0096             return false;
0097         }
0098 
0099         template <typename Component>
0100         bool call_variant(Component const& component, mpl::false_) const
0101         {
0102             // If Attribute is a variant, then search the variant types for a
0103             // suitable substitute type.
0104 
0105             typename
0106                 find_substitute<Attribute,
0107                     typename traits::attribute_of<Component, Context, Iterator>::type
0108                 >::type
0109             val;
0110 
0111             if (component.parse(first, last, context, skipper, val))
0112             {
0113                 traits::assign_to(val, attr);
0114                 return true;
0115             }
0116             return false;
0117         }
0118 
0119         template <typename Component>
0120         bool call_variant(Component const& component, mpl::true_) const
0121         {
0122             // If Attribute is a variant and the expected attribute is
0123             // the same type (pass the variant as-is).
0124 
0125             return component.parse(first, last, context, skipper, attr);
0126         }
0127 
0128         template <typename Component>
0129         bool call_optional_or_variant(Component const& component, mpl::false_) const
0130         {
0131             // Attribute is a variant...
0132 
0133             typedef typename
0134                 traits::attribute_of<Component, Context, Iterator>::type
0135             expected;
0136             return call_variant(component,
0137                 is_same<Attribute, expected>());
0138         }
0139 
0140         template <typename Component>
0141         bool call(Component const& component, mpl::false_) const
0142         {
0143             return call_optional_or_variant(
0144                 component, spirit::traits::not_is_variant<Attribute, qi::domain>());
0145         }
0146 
0147         template <typename Component>
0148         bool call_unused(Component const& component, mpl::true_) const
0149         {
0150             // return true if the parser succeeds
0151             return call(component,
0152                 mpl::and_<
0153                     spirit::traits::not_is_variant<Attribute, qi::domain>,
0154                     spirit::traits::not_is_optional<Attribute, qi::domain>
0155                 >());
0156         }
0157 
0158         template <typename Component>
0159         bool call_unused(Component const& component, mpl::false_) const
0160         {
0161             return component.parse(first, last, context, skipper, unused);
0162         }
0163 
0164         template <typename Component>
0165         bool operator()(Component const& component) const
0166         {
0167             // return true if the parser succeeds
0168             typedef typename traits::not_is_unused<
0169                 typename traits::attribute_of<Component, Context, Iterator>::type
0170             >::type predicate;
0171 
0172             return call_unused(component, predicate());
0173         }
0174 
0175         Iterator& first;
0176         Iterator const& last;
0177         Context& context;
0178         Skipper const& skipper;
0179         Attribute& attr;
0180     };
0181 
0182     template <typename Iterator, typename Context, typename Skipper>
0183     struct alternative_function<Iterator, Context, Skipper, unused_type const>
0184     {
0185         alternative_function(
0186             Iterator& first_, Iterator const& last_, Context& context_,
0187             Skipper const& skipper_, unused_type)
0188           : first(first_), last(last_), context(context_), skipper(skipper_)
0189         {
0190         }
0191 
0192         template <typename Component>
0193         bool operator()(Component const& component) const
0194         {
0195             // return true if the parser succeeds
0196             return component.parse(first, last, context, skipper,
0197                 unused);
0198         }
0199 
0200         Iterator& first;
0201         Iterator const& last;
0202         Context& context;
0203         Skipper const& skipper;
0204     };
0205 #ifdef _MSC_VER
0206 #  pragma warning(pop)
0207 #endif
0208 
0209 }}}}
0210 
0211 #endif