Boost C++ Libraries

boost/spirit/home/x3/support/context.hpp

/*=============================================================================
    Copyright (c) 2001-2014 Joel de Guzman
    http://spirit.sourceforge.net/

    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)
=============================================================================*/
#if !defined(BOOST_SPIRIT_X3_CONTEXT_JAN_4_2012_1215PM)
#define BOOST_SPIRIT_X3_CONTEXT_JAN_4_2012_1215PM

#include <boost/spirit/home/x3/support/unused.hpp>
#include <boost/mpl/identity.hpp>

namespace boost { namespace spirit { namespace x3
{
    template <typename ID, typename T, typename Next = unused_type>
    struct context
    {
        context(T& val, Next const& next)
            : val(val), next(next) {}

        T& get(mpl::identity<ID>) const
        {
            return val;
        }

        template <typename ID_>
        decltype(auto) get(ID_ id) const
        {
            return next.get(id);
        }

        T& val;
        Next const& next;
    };

    template <typename ID, typename T>
    struct context<ID, T, unused_type>
    {
        context(T& val)
            : val(val) {}

        context(T& val, unused_type)
            : val(val) {}

        T& get(mpl::identity<ID>) const
        {
            return val;
        }

        template <typename ID_>
        unused_type get(ID_) const
        {
            return {};
        }

        T& val;
    };

    template <typename Tag, typename Context>
    inline decltype(auto) get(Context const& context)
    {
        return context.get(mpl::identity<Tag>());
    }

    template <typename ID, typename T, typename Next>
    inline context<ID, T, Next> make_context(T& val, Next const& next)
    {
        return { val, next };
    }

    template <typename ID, typename T>
    inline context<ID, T> make_context(T& val)
    {
        return { val };
    }

    namespace detail
    {
        template <typename ID, typename T, typename Next, typename FoundVal>
        inline Next const&
        make_unique_context(T& /* val */, Next const& next, FoundVal&)
        {
            return next;
        }
        
        template <typename ID, typename T, typename Next>
        inline context<ID, T, Next>
        make_unique_context(T& val, Next const& next, unused_type)
        {
            return { val, next };
        }
    }

    template <typename ID, typename T, typename Next>
    inline auto
    make_unique_context(T& val, Next const& next)
    {
        return detail::make_unique_context<ID>(val, next, x3::get<ID>(next));
    }
}}}

#endif