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- /*=============================================================================
- Copyright (c) 2001-2011 Joel de Guzman
- Copyright (c) 2006 Dan Marsden
- 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(FUSION_VALUE_AT_IMPL_20060124_2129)
- #define FUSION_VALUE_AT_IMPL_20060124_2129
- #include <boost/fusion/support/config.hpp>
- #include <boost/fusion/container/vector/convert.hpp>
- #include <boost/fusion/algorithm/transformation/transform.hpp>
- #include <boost/fusion/sequence/intrinsic/value_at.hpp>
- #include <boost/type_traits/remove_reference.hpp>
- #include <boost/fusion/support/unused.hpp>
- #include <boost/mpl/eval_if.hpp>
- #include <boost/mpl/identity.hpp>
- #include <boost/type_traits/is_same.hpp>
- #include <boost/config.hpp>
- namespace boost { namespace fusion {
-
- struct zip_view_tag;
- namespace detail
- {
- template<typename N>
- struct poly_value_at
- {
- template<typename T>
- struct result;
- template<typename N1, typename Seq>
- struct result<poly_value_at<N1>(Seq)>
- : mpl::eval_if<is_same<Seq, unused_type const&>,
- mpl::identity<unused_type>,
- result_of::value_at<typename remove_reference<Seq>::type, N> >
- {};
- // never called, but needed for decltype-based result_of (C++0x)
- #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
- template<typename Seq>
- BOOST_FUSION_GPU_ENABLED
- typename result<poly_value_at(Seq)>::type
- operator()(Seq&&) const;
- #endif
- };
- }
-
- namespace extension
- {
- template<typename Tag>
- struct value_at_impl;
- template<>
- struct value_at_impl<zip_view_tag>
- {
- template<typename Sequence, typename N>
- struct apply
- {
- typedef typename result_of::transform<
- typename Sequence::sequences,
- detail::poly_value_at<N> >::type values;
- typedef typename result_of::as_vector<values>::type type;
- };
- };
- }
- }}
- #endif
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