ceph/src/boost/libs/spirit/include/boost/spirit/home/x3/operator/optional.hpp

   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(SPIRIT_OPTIONAL_MARCH_23_2007_1117PM)
   9 #define SPIRIT_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
  18 namespace 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 handles_container = true;
  25
  26         optional(Subject const& subject)
  27           : base_type(subject) {}
  28
  29         using base_type::parse_subject;
  30
  31         // Attribute is a container
  32         template <typename Iterator, typename Context
  33           , typename RContext, typename Attribute>
  34         bool parse_subject(Iterator& first, Iterator const& last
  35           , Context const& context, RContext& rcontext, Attribute& attr
  36           , traits::container_attribute) const
  37         {
  38             detail::parse_into_container(
  39                 this->subject, first, last, context, rcontext, attr);
  40             return true;
  41         }
  42
  43         // Attribute is an optional
  44         template <typename Iterator, typename Context
  45           , typename RContext, typename Attribute>
  46         bool parse_subject(Iterator& first, Iterator const& last
  47           , Context const& context, RContext& rcontext, Attribute& attr
  48           , traits::optional_attribute) const
  49         {
  50             typedef typename
  51                 x3::traits::optional_value<Attribute>::type
  52             value_type;
  53
  54             // create a local value
  55             value_type val = value_type();
  56
  57             if (this->subject.parse(first, last, context, rcontext, val))
  58             {
  59                 // assign the parsed value into our attribute
  60                 x3::traits::move_to(val, attr);
  61             }
  62             return true;
  63         }
  64     };
  65
  66     template <typename Subject>
  67     inline optional<typename extension::as_parser<Subject>::value_type>
  68     operator-(Subject const& subject)
  69     {
  70         return { as_parser(subject) };
  71     }
  72 }}}
  73
  74 namespace boost { namespace spirit { namespace x3 { namespace traits
  75 {
  76     template <typename Subject, typename Context>
  77     struct attribute_of<x3::optional<Subject>, Context>
  78         : build_optional<
  79             typename attribute_of<Subject, Context>::type> {};
  80 }}}}
  81
  82 #endif