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// Boost.Geometry (aka GGL, Generic Geometry Library)
// Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
// Copyright (c) 2008-2012 Bruno Lalande, Paris, France.
// Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
// Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
// (geolib/GGL), copyright (c) 1995-2010 Geodan, Amsterdam, the Netherlands.
// Use, modification and distribution is subject to 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_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP
#define BOOST_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP
#include <boost/mpl/equal_to.hpp>
#include <boost/mpl/fold.hpp>
#include <boost/mpl/front.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/insert.hpp>
#include <boost/mpl/int.hpp>
#include <boost/mpl/set.hpp>
#include <boost/mpl/size.hpp>
#include <boost/mpl/vector.hpp>
#include <boost/variant/variant_fwd.hpp>
namespace boost { namespace geometry
{
namespace detail
{
template <typename Variant>
struct unique_types:
mpl::fold<
typename mpl::reverse_fold<
typename Variant::types,
mpl::set<>,
mpl::insert<
mpl::placeholders::_1,
mpl::placeholders::_2
>
>::type,
mpl::vector<>,
mpl::push_back<mpl::placeholders::_1, mpl::placeholders::_2>
>
{};
template <typename Types>
struct variant_or_single:
mpl::if_<
mpl::equal_to<
mpl::size<Types>,
mpl::int_<1>
>,
typename mpl::front<Types>::type,
typename make_variant_over<Types>::type
>
{};
} // namespace detail
/*!
\brief Meta-function that takes a boost::variant type and tries to minimize
it by doing the following:
- if there's any duplicate types, remove them
- if the result is a variant of one type, turn it into just that type
\ingroup utility
\par Example
\code
typedef variant<int, float, int, long> variant_type;
typedef compress_variant<variant_type>::type compressed;
typedef mpl::vector<int, float, long> result_types;
BOOST_MPL_ASSERT(( mpl::equal<compressed::types, result_types> ));
typedef variant<int, int, int> one_type_variant_type;
typedef compress_variant<one_type_variant_type>::type single_type;
BOOST_MPL_ASSERT(( boost::equals<single_type, int> ));
\endcode
*/
template <typename Variant>
struct compress_variant:
detail::variant_or_single<
typename detail::unique_types<Variant>::type
>
{};
}} // namespace boost::geometry
#endif // BOOST_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP
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