boost/fusion/view/zip_view/detail/prior_impl.hpp
/*=============================================================================
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_PRIOR_IMPL_20060124_2006)
#define FUSION_PRIOR_IMPL_20060124_2006
#include <boost/fusion/view/zip_view/zip_view_iterator_fwd.hpp>
#include <boost/fusion/iterator/prior.hpp>
#include <boost/fusion/algorithm/transformation/transform.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/type_traits/remove_reference.hpp>
#include <boost/type_traits/remove_const.hpp>
namespace boost { namespace fusion {
struct zip_view_iterator_tag;
namespace detail
{
struct poly_prior
{
template<typename Sig>
struct result;
template<typename It>
struct result<poly_prior(It)>
{
typedef typename remove_const<
typename remove_reference<It>::type>::type it;
typedef typename mpl::eval_if<is_same<it, unused_type>,
mpl::identity<unused_type>,
result_of::prior<it> >::type type;
};
template<typename It>
typename result<poly_prior(It)>::type
operator()(const It& it) const
{
return fusion::prior(it);
}
unused_type operator()(unused_type const&) const
{
return unused_type();
}
};
}
namespace extension
{
template<typename Tag>
struct prior_impl;
template<>
struct prior_impl<zip_view_iterator_tag>
{
template<typename Iterator>
struct apply
{
typedef zip_view_iterator<
typename result_of::transform<typename Iterator::iterators, detail::poly_prior>::type,
typename Iterator::category> type;
static type
call(Iterator const& it)
{
return type(
fusion::transform(it.iterators_, detail::poly_prior()));
}
};
};
}
}}
#endif