1/*=============================================================================
2 Copyright (c) 2001-2014 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(BOOST_SPIRIT_X3_OPTIONAL_MARCH_23_2007_1117PM)
9#define BOOST_SPIRIT_X3_OPTIONAL_MARCH_23_2007_1117PM
10
11#include <boost/spirit/home/x3/core/proxy.hpp>
12#include <boost/spirit/home/x3/core/detail/parse_into_container.hpp>
13#include <boost/spirit/home/x3/support/traits/attribute_of.hpp>
14#include <boost/spirit/home/x3/support/traits/move_to.hpp>
15#include <boost/spirit/home/x3/support/traits/optional_traits.hpp>
16#include <boost/spirit/home/x3/support/traits/attribute_category.hpp>
17
18namespace boost { namespace spirit { namespace x3
19{
20 template <typename Subject>
21 struct optional : proxy<Subject, optional<Subject>>
22 {
23 typedef proxy<Subject, optional<Subject>> base_type;
24 static bool const is_pass_through_unary = false;
25 static bool const handles_container = true;
26
27 constexpr optional(Subject const& subject)
28 : base_type(subject) {}
29
30 using base_type::parse_subject;
31
32 // Attribute is a container
33 template <typename Iterator, typename Context
34 , typename RContext, typename Attribute>
35 bool parse_subject(Iterator& first, Iterator const& last
36 , Context const& context, RContext& rcontext, Attribute& attr
37 , traits::container_attribute) const
38 {
39 detail::parse_into_container(
40 this->subject, first, last, context, rcontext, attr);
41 return true;
42 }
43
44 // Attribute is an optional
45 template <typename Iterator, typename Context
46 , typename RContext, typename Attribute>
47 bool parse_subject(Iterator& first, Iterator const& last
48 , Context const& context, RContext& rcontext, Attribute& attr
49 , traits::optional_attribute) const
50 {
51 typedef typename
52 x3::traits::optional_value<Attribute>::type
53 value_type;
54
55 // create a local value
56 value_type val{};
57
58 if (this->subject.parse(first, last, context, rcontext, val))
59 {
60 // assign the parsed value into our attribute
61 x3::traits::move_to(val, attr);
62 }
63 return true;
64 }
65 };
66
67 template <typename Subject>
68 constexpr optional<typename extension::as_parser<Subject>::value_type>
69 operator-(Subject const& subject)
70 {
71 return { as_parser(subject) };
72 }
73}}}
74
75namespace boost { namespace spirit { namespace x3 { namespace traits
76{
77 template <typename Subject, typename Context>
78 struct attribute_of<x3::optional<Subject>, Context>
79 : build_optional<
80 typename attribute_of<Subject, Context>::type> {};
81}}}}
82
83#endif
84

source code of boost/libs/spirit/include/boost/spirit/home/x3/operator/optional.hpp