text: /*=============================================================================
      Copyright (c) 2014 Joel de Guzman
  
      Distributed under the Boost Software License, Version 1.0. (See accompanying
      file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  =============================================================================*/
  #ifndef BOOST_SPIRIT_X3_DIRECTIVE_WITH_HPP
  #define BOOST_SPIRIT_X3_DIRECTIVE_WITH_HPP
  
  #include <boost/spirit/home/x3/support/unused.hpp>
  #include <boost/spirit/home/x3/core/parser.hpp>
  
  namespace boost { namespace spirit { namespace x3
  {
      ///////////////////////////////////////////////////////////////////////////
      // with directive injects a value into the context prior to parsing.
      ///////////////////////////////////////////////////////////////////////////
      template <typename Subject, typename Derived, typename T>
      struct with_value_holder
        : unary_parser<Subject, Derived>
      {
          typedef unary_parser<Subject, Derived> base_type;
          mutable T val;
          constexpr with_value_holder(Subject const& subject, T&& val)
            : base_type(subject)
            , val(std::forward<T>(val)) {}
      };
      
      template <typename Subject, typename Derived, typename T>
      struct with_value_holder<Subject, Derived, T&>
        : unary_parser<Subject, Derived>
      {
          typedef unary_parser<Subject, Derived> base_type;
          T& val;
          constexpr with_value_holder(Subject const& subject, T& val)
            : base_type(subject)
            , val(val) {}
      };
  
      template <typename Subject, typename ID, typename T>
      struct with_directive
        : with_value_holder<Subject, with_directive<Subject, ID, T>, T>
      {
          typedef with_value_holder<Subject, with_directive<Subject, ID, T>, T> base_type;
          static bool const is_pass_through_unary = true;
          static bool const handles_container = Subject::handles_container;
  
          typedef Subject subject_type;
  
          constexpr with_directive(Subject const& subject, T&& val)
            : base_type(subject, std::forward<T>(val)) {}
  
          template <typename Iterator, typename Context
            , typename RContext, typename Attribute>
          bool parse(Iterator& first, Iterator const& last
            , Context const& context, RContext& rcontext, Attribute& attr) const
          {
              return this->subject.parse(
                  first, last
                , make_context<ID>(this->val, context)
                , rcontext
                , attr);
          }
      };
     
      template <typename ID, typename T>
      struct with_gen
      {
          T&& val;
  
          template <typename Subject>
          constexpr with_directive<typename extension::as_parser<Subject>::value_type, ID, T>
          operator[](Subject const& subject) const
          {
              return { as_parser(subject), std::forward<T>(val) };
          }
      };
  
      template <typename ID, typename T>
      constexpr with_gen<ID, T> with(T&& val)
      {
          return { std::forward<T>(val) };
      }
  }}}
  
  #endif
  