filterRangeFor.h

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#ifndef LARDATA_UTILITIES_FILTERRANGEFOR_H
#define LARDATA_UTILITIES_FILTERRANGEFOR_H

// Boost libraries
#include <boost/iterator/filter_iterator.hpp>

namespace util {

  template <typename Range, typename Pred>
  auto filterRangeFor(Range&& range, Pred&& pred) -> decltype(auto);

} // namespace util

//------------------------------------------------------------------------------
//--- implementation
//------------------------------------------------------------------------------
namespace util {

  namespace details {

    //--------------------------------------------------------------------------
    template <typename Range, typename Pred>
    class FilterRangeForStruct {

      static auto getBegin(Range&& range) -> decltype(auto)
      {
        using std::begin;
        return begin(range);
      }

      static auto getEnd(Range&& range) -> decltype(auto)
      {
        using std::end;
        return end(range);
      }

      static auto makeBeginIterator(Range&& range, Pred&& pred)
      {
        auto begin = getBegin(std::forward<Range>(range));
        auto end = getEnd(std::forward<Range>(range));
        return boost::make_filter_iterator(std::forward<Pred>(pred), begin, end);
      }

      static auto makeEndIterator(Range&& range, Pred&& pred)
      {
        auto end = getEnd(std::forward<Range>(range));
        return boost::make_filter_iterator(std::forward<Pred>(pred), end, end);
      }

      using begin_iterator_t =
        decltype(makeBeginIterator(std::declval<Range&&>(), std::declval<Pred&&>()));
      using end_iterator_t =
        decltype(makeEndIterator(std::declval<Range&&>(), std::declval<Pred&&>()));

      begin_iterator_t fBegin;
      end_iterator_t fEnd;

    public:
      FilterRangeForStruct(Range&& range, Pred&& pred)
        : fBegin(makeBeginIterator(std::forward<Range>(range), std::forward<Pred>(pred)))
        , fEnd(makeEndIterator(std::forward<Range>(range), std::forward<Pred>(pred)))
      {}

      auto begin() const { return fBegin; }
      auto end() const { return fEnd; }

    }; // class FilterRangeForStruct<>

    //--------------------------------------------------------------------------

  } // namespace details

  //----------------------------------------------------------------------------
  template <typename Range, typename Pred>
  auto filterRangeFor(Range&& range, Pred&& pred) -> decltype(auto)
  {
    return details::FilterRangeForStruct<Range, Pred>(std::forward<Range>(range),
                                                      std::forward<Pred>(pred));
  }

  //----------------------------------------------------------------------------

} // namespace util

//------------------------------------------------------------------------------

#endif // LARDATA_UTILITIES_FILTERRANGEFOR_H