x3/support/subcontext.hpp

0001 /*=============================================================================
0002     Copyright (c) 2001-2014 Joel de Guzman
0003     Copyright (c) 2013 Agustin Berge
0004     http://spirit.sourceforge.net/
0005
0006     Distributed under the Boost Software License, Version 1.0. (See accompanying
0007     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0008 =============================================================================*/
0009 #if !defined(BOOST_SPIRIT_X3_SUBCONTEXT_APR_15_2013_0840AM)
0010 #define BOOST_SPIRIT_X3_SUBCONTEXT_APR_15_2013_0840AM
0011
0012 #include <boost/spirit/home/x3/support/context.hpp>
0013 #include <boost/spirit/home/x3/support/unused.hpp>
0014
0015 namespace boost { namespace spirit { namespace x3
0016 {
0017     template <typename... T>
0018     struct subcontext;
0019
0020     template <>
0021     struct subcontext<>
0022     {
0023         template <typename Context>
0024         subcontext(Context const& /*context*/)
0025         {}
0026
0027         template <typename ID_>
0028         unused_type
0029         get(ID_) const
0030         {
0031             return unused;
0032         }
0033     };
0034
0035     template <typename T>
0036     struct subcontext<T>
0037       : context<typename T::first_type, typename T::second_type>
0038     {
0039         typedef context<
0040             typename T::first_type, typename T::second_type
0041         > context_type;
0042
0043         template <typename Context>
0044         subcontext(Context const& context)
0045           : context_type(x3::get<typename T::first_type>(context))
0046         {}
0047
0048         using context_type::get;
0049     };
0050
0051     template <typename T, typename... Tail>
0052     struct subcontext<T, Tail...>
0053       : subcontext<Tail...>
0054       , context<
0055             typename T::first_type, typename T::second_type
0056           , subcontext<Tail...>
0057         >
0058     {
0059         typedef subcontext<Tail...> base_type;
0060         typedef context<
0061             typename T::first_type, typename T::second_type
0062           , base_type
0063         > context_type;
0064
0065         template <typename Context>
0066         subcontext(Context const& context)
0067           : base_type(context)
0068           , context_type(
0069                 x3::get<typename T::first_type>(context)
0070               , *static_cast<base_type*>(this))
0071         {}
0072
0073         using context_type::get;
0074     };
0075
0076 }}}
0077
0078 #endif