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#ifndef BOOST_SPIRIT_QI_OPERATOR_OPTIONAL_HPP
9#define BOOST_SPIRIT_QI_OPERATOR_OPTIONAL_HPP
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 <boost/proto/operators.hpp>
26#include <boost/proto/tags.hpp>
27#include <vector>
28
29namespace boost { namespace spirit
30{
31 ///////////////////////////////////////////////////////////////////////////
32 // Enablers
33 ///////////////////////////////////////////////////////////////////////////
34 template <>
35 struct use_operator<qi::domain, proto::tag::negate> // enables -p
36 : mpl::true_ {};
37}}
38
39namespace boost { namespace spirit { namespace qi
40{
41 template <typename Subject>
42 struct optional : unary_parser<optional<Subject> >
43 {
44 typedef Subject subject_type;
45
46 template <typename Context, typename Iterator>
47 struct attribute
48 {
49 // Build a boost::optional from the subject's attribute. Note
50 // that boost::optional may return unused_type if the
51 // subject's attribute is an unused_type.
52 typedef typename
53 traits::build_optional<
54 typename traits::
55 attribute_of<Subject, Context, Iterator>::type
56 >::type
57 type;
58 };
59
60 optional(Subject const& subject_)
61 : subject(subject_) {}
62
63 template <typename Iterator, typename Context
64 , typename Skipper, typename Attribute>
65 bool parse_impl(Iterator& first, Iterator const& last
66 , Context& context, Skipper const& skipper
67 , Attribute& attr_, mpl::false_) const
68 {
69 // create a local value if Attribute is not unused_type
70 typename spirit::result_of::optional_value<Attribute>::type val =
71 typename spirit::result_of::optional_value<Attribute>::type();
72
73 if (subject.parse(first, last, context, skipper, val))
74 {
75 // assign the parsed value into our attribute
76 spirit::traits::assign_to(val, attr_);
77 }
78 return true;
79 }
80
81 template <typename Iterator, typename Context
82 , typename Skipper, typename Attribute>
83 bool parse_impl(Iterator& first, Iterator const& last
84 , Context& context, Skipper const& skipper
85 , Attribute& attr_, mpl::true_) const
86 {
87 subject.parse(first, last, context, skipper, attr_);
88 return true;
89 }
90
91 template <typename Iterator, typename Context
92 , typename Skipper, typename Attribute>
93 bool parse(Iterator& first, Iterator const& last
94 , Context& context, Skipper const& skipper
95 , Attribute& attr_) const
96 {
97 typedef typename spirit::result_of::optional_value<Attribute>::type
98 attribute_type;
99
100 return parse_impl(first, last, context, skipper, attr_
101 , traits::is_container<attribute_type>());
102 }
103
104 template <typename Context>
105 info what(Context& context) const
106 {
107 return info("optional", subject.what(context));
108 }
109
110 Subject subject;
111 };
112
113 ///////////////////////////////////////////////////////////////////////////
114 // Parser generators: make_xxx function (objects)
115 ///////////////////////////////////////////////////////////////////////////
116 template <typename Elements, typename Modifiers>
117 struct make_composite<proto::tag::negate, Elements, Modifiers>
118 : make_unary_composite<Elements, optional>
119 {};
120}}}
121
122namespace boost { namespace spirit { namespace traits
123{
124 ///////////////////////////////////////////////////////////////////////////
125 template <typename Subject>
126 struct has_semantic_action<qi::optional<Subject> >
127 : unary_has_semantic_action<Subject> {};
128
129 ///////////////////////////////////////////////////////////////////////////
130 template <typename Subject, typename Attribute, typename Context
131 , typename Iterator>
132 struct handles_container<qi::optional<Subject>, Attribute
133 , Context, Iterator>
134 : mpl::true_ {};
135}}}
136
137#endif
138

source code of boost/libs/spirit/include/boost/spirit/home/qi/operator/optional.hpp