107 lines
3.1 KiB
C++
107 lines
3.1 KiB
C++
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// Boost.Geometry (aka GGL, Generic Geometry Library)
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// Copyright (c) 2007-2015 Barend Gehrels, Amsterdam, the Netherlands.
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// Copyright (c) 2008-2015 Bruno Lalande, Paris, France.
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// Copyright (c) 2009-2015 Mateusz Loskot, London, UK.
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// This file was modified by Oracle on 2015.
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// Modifications copyright (c) 2015, Oracle and/or its affiliates.
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// Contributed and/or modified by Menelaos Karavelas, on behalf of Oracle
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// Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
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// (geolib/GGL), copyright (c) 1995-2010 Geodan, Amsterdam, the Netherlands.
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// Use, modification and distribution is subject to the Boost Software License,
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// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP
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#define BOOST_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP
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#include <boost/mpl/equal_to.hpp>
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#include <boost/mpl/fold.hpp>
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#include <boost/mpl/front.hpp>
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#include <boost/mpl/if.hpp>
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#include <boost/mpl/insert.hpp>
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#include <boost/mpl/int.hpp>
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#include <boost/mpl/set.hpp>
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#include <boost/mpl/size.hpp>
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#include <boost/mpl/vector.hpp>
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#include <boost/variant/variant_fwd.hpp>
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namespace boost { namespace geometry
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{
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namespace detail
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{
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template <typename Variant>
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struct unique_types:
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boost::mpl::fold<
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typename boost::mpl::reverse_fold<
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typename Variant::types,
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boost::mpl::set<>,
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boost::mpl::insert<
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boost::mpl::placeholders::_1,
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boost::mpl::placeholders::_2
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>
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>::type,
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boost::mpl::vector<>,
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boost::mpl::push_back
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<
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boost::mpl::placeholders::_1, boost::mpl::placeholders::_2
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>
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>
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{};
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template <typename Types>
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struct variant_or_single:
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boost::mpl::if_<
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boost::mpl::equal_to<
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boost::mpl::size<Types>,
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boost::mpl::int_<1>
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>,
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typename boost::mpl::front<Types>::type,
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typename make_variant_over<Types>::type
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>
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{};
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} // namespace detail
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/*!
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\brief Meta-function that takes a boost::variant type and tries to minimize
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it by doing the following:
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- if there's any duplicate types, remove them
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- if the result is a variant of one type, turn it into just that type
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\ingroup utility
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\par Example
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\code
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typedef variant<int, float, int, long> variant_type;
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typedef compress_variant<variant_type>::type compressed;
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typedef boost::mpl::vector<int, float, long> result_types;
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BOOST_MPL_ASSERT(( boost::mpl::equal<compressed::types, result_types> ));
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typedef variant<int, int, int> one_type_variant_type;
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typedef compress_variant<one_type_variant_type>::type single_type;
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BOOST_MPL_ASSERT(( boost::equals<single_type, int> ));
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\endcode
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*/
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template <typename Variant>
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struct compress_variant:
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detail::variant_or_single<
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typename detail::unique_types<Variant>::type
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>
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{};
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}} // namespace boost::geometry
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#endif // BOOST_GEOMETRY_UTIL_COMPRESS_VARIANT_HPP
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