// 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