1 /*=============================================================================
2     Copyright (c) 2001-2011 Joel de Guzman
3     Copyright (c) 2001-2011 Hartmut Kaiser
4 
5     Distributed under the Boost Software License, Version 1.0. (See accompanying
6     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7 =============================================================================*/
8 #if !defined(SPIRIT_OPTIONAL_MARCH_23_2007_1117PM)
9 #define SPIRIT_OPTIONAL_MARCH_23_2007_1117PM
10 
11 #if defined(_MSC_VER)
12 #pragma once
13 #endif
14 
15 #include <boost/spirit/home/support/unused.hpp>
16 #include <boost/spirit/home/qi/detail/attributes.hpp>
17 #include <boost/spirit/home/support/has_semantic_action.hpp>
18 #include <boost/spirit/home/support/handles_container.hpp>
19 #include <boost/spirit/home/support/info.hpp>
20 #include <boost/spirit/home/support/container.hpp>
21 #include <boost/spirit/home/qi/parser.hpp>
22 #include <boost/spirit/home/qi/meta_compiler.hpp>
23 #include <boost/spirit/home/qi/detail/assign_to.hpp>
24 #include <boost/optional.hpp>
25 #include <vector>
26 
27 namespace boost { namespace spirit
28 {
29     ///////////////////////////////////////////////////////////////////////////
30     // Enablers
31     ///////////////////////////////////////////////////////////////////////////
32     template <>
33     struct use_operator<qi::domain, proto::tag::negate> // enables -p
34       : mpl::true_ {};
35 }}
36 
37 namespace boost { namespace spirit { namespace qi
38 {
39     template <typename Subject>
40     struct optional : unary_parser<optional<Subject> >
41     {
42         typedef Subject subject_type;
43 
44         template <typename Context, typename Iterator>
45         struct attribute
46         {
47             // Build a boost::optional from the subject's attribute. Note
48             // that boost::optional may return unused_type if the
49             // subject's attribute is an unused_type.
50             typedef typename
51                 traits::build_optional<
52                     typename traits::
53                         attribute_of<Subject, Context, Iterator>::type
54                 >::type
55             type;
56         };
57 
optionalboost::spirit::qi::optional58         optional(Subject const& subject)
59           : subject(subject) {}
60 
61         template <typename Iterator, typename Context
62           , typename Skipper, typename Attribute>
parse_implboost::spirit::qi::optional63         bool parse_impl(Iterator& first, Iterator const& last
64           , Context& context, Skipper const& skipper
65           , Attribute& attr, mpl::false_) const
66         {
67             // create a local value if Attribute is not unused_type
68             typename spirit::result_of::optional_value<Attribute>::type val =
69                 typename spirit::result_of::optional_value<Attribute>::type();
70 
71             if (subject.parse(first, last, context, skipper, val))
72             {
73                 // assign the parsed value into our attribute
74                 spirit::traits::assign_to(val, attr);
75             }
76             return true;
77         }
78 
79         template <typename Iterator, typename Context
80           , typename Skipper, typename Attribute>
parse_implboost::spirit::qi::optional81         bool parse_impl(Iterator& first, Iterator const& last
82           , Context& context, Skipper const& skipper
83           , Attribute& attr, mpl::true_) const
84         {
85             subject.parse(first, last, context, skipper, attr);
86             return true;
87         }
88 
89         template <typename Iterator, typename Context
90           , typename Skipper, typename Attribute>
parseboost::spirit::qi::optional91         bool parse(Iterator& first, Iterator const& last
92           , Context& context, Skipper const& skipper
93           , Attribute& attr) const
94         {
95             typedef typename spirit::result_of::optional_value<Attribute>::type
96                 attribute_type;
97 
98             return parse_impl(first, last, context, skipper, attr
99               , traits::is_container<attribute_type>());
100         }
101 
102         template <typename Context>
whatboost::spirit::qi::optional103         info what(Context& context) const
104         {
105             return info("optional", subject.what(context));
106         }
107 
108         Subject subject;
109     };
110 
111     ///////////////////////////////////////////////////////////////////////////
112     // Parser generators: make_xxx function (objects)
113     ///////////////////////////////////////////////////////////////////////////
114     template <typename Elements, typename Modifiers>
115     struct make_composite<proto::tag::negate, Elements, Modifiers>
116       : make_unary_composite<Elements, optional>
117     {};
118 }}}
119 
120 namespace boost { namespace spirit { namespace traits
121 {
122     ///////////////////////////////////////////////////////////////////////////
123     template <typename Subject>
124     struct has_semantic_action<qi::optional<Subject> >
125       : unary_has_semantic_action<Subject> {};
126 
127     ///////////////////////////////////////////////////////////////////////////
128     template <typename Subject, typename Attribute, typename Context
129         , typename Iterator>
130     struct handles_container<qi::optional<Subject>, Attribute
131           , Context, Iterator>
132       : mpl::true_ {};
133 }}}
134 
135 #endif
136