iterators.h

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#ifndef ZYPP_CORE_NG_BASE_ITERATORS_H_INCLUDED
#define ZYPP_CORE_NG_BASE_ITERATORS_H_INCLUDED

#include <iterator>
#include <utility>

namespace zyppng {

  template<class Pred, class Base>
  class FilterIterator {
  public:
    using iterator_category = std::forward_iterator_tag;
    using value_type        = typename std::iterator_traits<Base>::value_type;
    using difference_type   = typename std::iterator_traits<Base>::difference_type;
    using pointer           = typename std::iterator_traits<Base>::pointer;
    using reference         = typename std::iterator_traits<Base>::reference;

    FilterIterator() = default;

    FilterIterator(Pred p, Base it, Base end) 
      : _pred(std::move(p)), _it(std::move(it)), _end(std::move(end)) 
    {
      satisfy_predicate();
    }

    reference operator*() const { return *_it; }
    
    pointer operator->() const { return &(*_it); }

    FilterIterator& operator++() {
      ++_it;
      satisfy_predicate();
      return *this;
    }

    FilterIterator operator++(int) {
      FilterIterator tmp = *this;
      ++(*this);
      return tmp;
    }

    bool operator==(const FilterIterator& other) const {
      return _it == other._it;
    }

    bool operator!=(const FilterIterator& other) const {
      return !(*this == other);
    }

    Base const & base() const { return _it; }

  private:
    void satisfy_predicate() {
      while (_it != _end && !_pred(*_it)) {
        ++_it;
      }
    }

    Pred _pred;
    Base _it;
    Base _end;
  };

  template<class Pred, class Base>
  FilterIterator<Pred, Base> make_filter_iterator(Pred p, Base it, Base end) {
    return FilterIterator<Pred, Base>(std::move(p), std::move(it), std::move(end));
  }

} // namespace zyppng

#endif