boost/fusion/algorithm/query/detail/count.hpp

/*=============================================================================
    Copyright (c) 2001-2006 Joel de Guzman

    Distributed under 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)
==============================================================================*/
#if !defined(FUSION_COUNT_09162005_0158)
#define FUSION_COUNT_09162005_0158

#include <boost/mpl/or.hpp>
#include <boost/type_traits/is_convertible.hpp>
#include <boost/fusion/support/detail/access.hpp>

namespace boost { namespace fusion { namespace detail
{ 
    template <bool is_convertible>
    struct compare_convertible;

    // T1 is convertible to T2 or vice versa
    template <>
    struct compare_convertible<true> 
    {
        template <typename T1, typename T2>
        static bool
        call(T1 const& x, T2 const& y)
        {
            return x == y;
        }
    };

    // T1 is NOT convertible to T2 NOR vice versa
    template <>
    struct compare_convertible<false>
    {
        template <typename T1, typename T2>
        static bool
        call(T1 const&, T2 const&)
        {
            return false;
        }
    };

    template <typename T1>
    struct count_compare
    {
        typedef typename detail::call_param<T1>::type param;
        count_compare(param x)
            : x(x) {}

        template <typename T2>
        bool
        operator()(T2 const& y)
        {
            return 
                compare_convertible<
                    mpl::or_<
                        is_convertible<T1, T2>
                      , is_convertible<T2, T1> 
                    >::value
                >::call(x, y);
        }

        param x;
    };
}}}

#endif