1 //  Copyright (c) 2001-2011 Joel de Guzman
2 //  Copyright (c) 2001-2011 Hartmut Kaiser
3 //
4 //  Distributed under the Boost Software License, Version 1.0. (See accompanying
5 //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 
7 #ifndef BOOST_SPIRIT_KARMA_OPERATOR_OPTIONAL_HPP
8 #define BOOST_SPIRIT_KARMA_OPERATOR_OPTIONAL_HPP
9 
10 #if defined(_MSC_VER)
11 #pragma once
12 #endif
13 
14 #include <boost/spirit/home/karma/domain.hpp>
15 #include <boost/spirit/home/karma/generator.hpp>
16 #include <boost/spirit/home/karma/meta_compiler.hpp>
17 #include <boost/spirit/home/support/info.hpp>
18 #include <boost/spirit/home/support/unused.hpp>
19 #include <boost/spirit/home/karma/detail/attributes.hpp>
20 #include <boost/spirit/home/support/container.hpp>
21 #include <boost/spirit/home/support/has_semantic_action.hpp>
22 #include <boost/spirit/home/support/handles_container.hpp>
23 #include <boost/mpl/assert.hpp>
24 #include <boost/optional.hpp>
25 #include <boost/proto/operators.hpp>
26 #include <boost/proto/tags.hpp>
27 #include <boost/type_traits/is_convertible.hpp>
28 
29 namespace boost { namespace spirit
30 {
31     ///////////////////////////////////////////////////////////////////////////
32     // Enablers
33     ///////////////////////////////////////////////////////////////////////////
34     template <>
35     struct use_operator<karma::domain, proto::tag::negate> // enables -g
36       : mpl::true_ {};
37 
38 }}
39 
40 ///////////////////////////////////////////////////////////////////////////////
41 namespace boost { namespace spirit { namespace karma
42 {
43     ///////////////////////////////////////////////////////////////////////////
44     template <typename Subject>
45     struct optional : unary_generator<optional<Subject> >
46     {
47         typedef Subject subject_type;
48         typedef typename subject_type::properties properties;
49 
50         // Build a boost::optional from the subject's attribute. Note
51         // that boost::optional may return unused_type if the
52         // subject's attribute is an unused_type.
53         template <typename Context, typename Iterator = unused_type>
54         struct attribute
55           : traits::build_optional<
56                 typename traits::attribute_of<Subject, Context, Iterator>::type
57             >
58         {};
59 
optionalboost::spirit::karma::optional60         optional(Subject const& subject)
61           : subject(subject) {}
62 
63         template <
64             typename OutputIterator, typename Context, typename Delimiter
65           , typename Attribute>
generateboost::spirit::karma::optional66         bool generate(OutputIterator& sink, Context& ctx
67           , Delimiter const& d, Attribute const& attr) const
68         {
69             if (traits::has_optional_value(attr))
70                 subject.generate(sink, ctx, d, traits::optional_value(attr));
71             return sink_is_good(sink);
72         }
73 
74         template <typename Context>
whatboost::spirit::karma::optional75         info what(Context& context) const
76         {
77             return info("optional", subject.what(context));
78         }
79 
80         Subject subject;
81     };
82 
83     ///////////////////////////////////////////////////////////////////////////
84     // Generator generators: make_xxx function (objects)
85     ///////////////////////////////////////////////////////////////////////////
86     template <typename Elements, typename Modifiers>
87     struct make_composite<proto::tag::negate, Elements, Modifiers>
88       : make_unary_composite<Elements, optional> {};
89 
90 }}}
91 
92 namespace boost { namespace spirit { namespace traits
93 {
94     ///////////////////////////////////////////////////////////////////////////
95     template <typename Subject>
96     struct has_semantic_action<karma::optional<Subject> >
97       : unary_has_semantic_action<Subject> {};
98 
99     ///////////////////////////////////////////////////////////////////////////
100     template <typename Subject, typename Attribute, typename Context
101       , typename Iterator>
102     struct handles_container<karma::optional<Subject>, Attribute, Context
103           , Iterator>
104       : mpl::true_ {};
105 }}}
106 
107 #endif
108