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// Copyright David Abrahams 2003. 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 MINIMUM_CATEGORY_DWA20031119_HPP
# define MINIMUM_CATEGORY_DWA20031119_HPP
# include <boost/type_traits/is_convertible.hpp>
# include <boost/type_traits/is_same.hpp>
# include <boost/mpl/aux_/lambda_support.hpp>
namespace boost { namespace detail {
//
// Returns the minimum category type or error_type
// if T1 and T2 are unrelated.
//
// For compilers not supporting is_convertible this only
// works with the new boost return and traversal category
// types. The exact boost _types_ are required. No derived types
// will work.
//
//
template <bool GreaterEqual, bool LessEqual>
struct minimum_category_impl
# if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
{
template <class T1, class T2> struct apply
{
typedef T2 type;
};
typedef void type;
}
# endif
;
template <class T1, class T2>
struct error_not_related_by_convertibility;
template <>
struct minimum_category_impl<true,false>
{
template <class T1, class T2> struct apply
{
typedef T2 type;
};
};
template <>
struct minimum_category_impl<false,true>
{
template <class T1, class T2> struct apply
{
typedef T1 type;
};
};
template <>
struct minimum_category_impl<true,true>
{
template <class T1, class T2> struct apply
{
BOOST_STATIC_ASSERT((is_same<T1,T2>::value));
typedef T1 type;
};
};
template <>
struct minimum_category_impl<false,false>
{
template <class T1, class T2> struct apply
: error_not_related_by_convertibility<T1,T2>
{
};
};
template <class T1 = mpl::_1, class T2 = mpl::_2>
struct minimum_category
{
typedef minimum_category_impl<
# if BOOST_WORKAROUND(BOOST_MSVC, < 1300) // ETI workaround
is_same<T2,int>::value ||
# endif
::boost::is_convertible<T1,T2>::value
, ::boost::is_convertible<T2,T1>::value
# if BOOST_WORKAROUND(BOOST_MSVC, < 1300) // ETI workaround
|| is_same<T1,int>::value
# endif
> outer;
typedef typename outer::template apply<T1,T2> inner;
typedef typename inner::type type;
BOOST_MPL_AUX_LAMBDA_SUPPORT(2,minimum_category,(T1,T2))
};
template <>
struct minimum_category<mpl::_1,mpl::_2>
{
template <class T1, class T2>
struct apply : minimum_category<T1,T2>
{};
BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(2,minimum_category,(mpl::_1,mpl::_2))
};
# if BOOST_WORKAROUND(BOOST_MSVC, < 1300) // ETI workaround
template <>
struct minimum_category<int,int>
{
typedef int type;
};
# endif
}} // namespace boost::detail
#endif // MINIMUM_CATEGORY_DWA20031119_HPP
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