Duplicates.h

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 *
 * Copyright (c) 2008-2010 Michael Schulze <mschulze@ivs.cs.uni-magdeburg.de>
 *                    2010 Marcus Foerster <MarcusFoerster1@gmx.de>
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#ifndef _Duplicates_h_
#define _Duplicates_h_

#include "boost/mpl/begin.hpp"
#include "boost/mpl/end.hpp"
#include "boost/mpl/next.hpp"
#include "boost/mpl/deref.hpp"

#include "boost/mpl/eval_if.hpp"
#include "boost/mpl/count_if.hpp"

#include "mw/attributes/type_traits/is_same_base_type.h"

namespace famouso {
    namespace mw {
        namespace attributes {
            namespace detail {

                template <typename AttrSeq, typename Iter = typename boost::mpl::begin<AttrSeq>::type>
                struct Duplicates {
                    private:
                        // The current attribute
                        typedef boost::mpl::deref<Iter> curAttr;

                        // A predicate testing every attribute of the sequence against the current
                        //  one based on the base type
                        typedef famouso::mw::attributes::type_traits::is_same_base_type<
                                                                            boost::mpl::_1,
                                                                            typename curAttr::type
                                                                      > pred;

                        // The number of attributes in the sequence matching the current one
                        typedef typename boost::mpl::count_if<AttrSeq, pred> currentCount;

                        // The iterator pointing to the next attribute in the sequence
                        typedef boost::mpl::next<Iter> nextIter;

                        // The Duplicates struct using the next iterator
                        typedef Duplicates<AttrSeq, typename nextIter::type> nextDupl;

                    public:
                        static const bool result = (currentCount::value > 1) ? true : nextDupl::result;

                        typedef typename boost::mpl::eval_if_c<
                                                      result,
                                                      typename curAttr::type,
                                                      typename nextDupl::duplicateAttribute
                                                     >::type duplicateAttribute;
                };

                template <typename AttrSeq>
                struct Duplicates<AttrSeq, typename boost::mpl::end<AttrSeq>::type> {
                    private:
                        struct Dummy {
                            typedef Dummy type;
                        };

                    public:
                        // \todo: Could anyone please tell me why a static const member is
                        //  not "constant enough" so that I must use this ugly enum?!
                        // (and why is it sufficient in the general template definition above?!)
                        enum {
                            result = false
                        };

                        typedef Dummy duplicateAttribute;
                };

            }  // end namespace detail
        }  // end namespace attributes
    }  // end namespace mw
}  // end namespace famouso

#endif