// Copyright David Abrahams 2003. Use, modification and distribution is
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// subject to the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_ITERATOR_MINIMUM_CATEGORY_HPP_INCLUDED_
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# define BOOST_ITERATOR_MINIMUM_CATEGORY_HPP_INCLUDED_
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# include <boost/static_assert.hpp>
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# include <boost/type_traits/is_convertible.hpp>
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# include <boost/type_traits/is_same.hpp>
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# include <boost/mpl/placeholders.hpp>
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# include <boost/mpl/aux_/lambda_support.hpp>
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namespace boost {
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namespace iterators {
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namespace detail {
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template <bool GreaterEqual, bool LessEqual>
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struct minimum_category_impl;
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template <class T1, class T2>
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struct error_not_related_by_convertibility;
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template <>
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struct minimum_category_impl<true,false>
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{
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template <class T1, class T2> struct apply
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{
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typedef T2 type;
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};
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};
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template <>
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struct minimum_category_impl<false,true>
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{
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template <class T1, class T2> struct apply
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{
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typedef T1 type;
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};
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};
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template <>
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struct minimum_category_impl<true,true>
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{
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template <class T1, class T2> struct apply
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{
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BOOST_STATIC_ASSERT((is_same<T1,T2>::value));
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typedef T1 type;
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};
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};
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template <>
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struct minimum_category_impl<false,false>
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{
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template <class T1, class T2> struct apply
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: error_not_related_by_convertibility<T1,T2>
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{
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};
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};
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} // namespace detail
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//
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// Returns the minimum category type or fails to compile
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// if T1 and T2 are unrelated.
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//
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template <class T1 = mpl::_1, class T2 = mpl::_2>
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struct minimum_category
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{
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typedef boost::iterators::detail::minimum_category_impl<
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::boost::is_convertible<T1,T2>::value
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, ::boost::is_convertible<T2,T1>::value
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> outer;
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typedef typename outer::template apply<T1,T2> inner;
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typedef typename inner::type type;
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BOOST_MPL_AUX_LAMBDA_SUPPORT(2,minimum_category,(T1,T2))
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};
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template <>
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struct minimum_category<mpl::_1,mpl::_2>
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{
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template <class T1, class T2>
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struct apply : minimum_category<T1,T2>
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{};
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BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(2,minimum_category,(mpl::_1,mpl::_2))
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};
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} // namespace iterators
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} // namespace boost
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#endif // BOOST_ITERATOR_MINIMUM_CATEGORY_HPP_INCLUDED_
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