cpp-useful-iterators/filter_iterator.hpp

//
//  filter_iterator.hpp
//  iterator
//
//  Created by Sam Jaffe on 6/17/17.
//

#pragma once

#include "end_aware_iterator.hpp"

namespace iterator {
  template <typename Iter>
  class filter_iterator : public end_aware_iterator<Iter> {
  private:
    using super = end_aware_iterator<Iter>;
  public:
    using value_type = typename super::value_type;
    using reference = typename super::reference;
    using pointer = typename super::pointer;
    using difference_type = typename super::difference_type;
    using iterator_category = typename super::iterator_category;
  public:
    filter_iterator() = default;
    template <typename... Args>
    filter_iterator(std::function<bool(value_type const &)> && p, Args &&... super_args)
    : super(std::forward<Args>(super_args)...)
    , pred(std::move(p)) {
      if (should_advance()) { advance(); }
    }
    
    filter_iterator & operator++() {
      advance();
      return *this;
    }
    
    filter_iterator operator++(int) {
      filter_iterator tmp{*this};
      operator++();
      return tmp;
    }
  private:
    bool should_advance() {
      return !super::done() && !pred(super::operator*());
    }
    void advance() {
      do { super::operator++(); } while (should_advance());
    }
    std::function<bool(value_type const &)> pred;
  };
}

template <typename Pred, typename Iter>
iterator::filter_iterator<Iter> make_filter_iterator(Pred && p, Iter it, Iter end) { return {p, it, end}; }

template <typename Pred, typename C>
auto make_filter_iterator(Pred && p, C & collect) -> iterator::filter_iterator<decltype(std::begin(collect))> {
  return { p, std::begin(collect), std::end(collect) };
}

template <typename Pred, typename C>
auto make_filter_iterator(Pred && p, C const & collect) -> iterator::filter_iterator<decltype(std::begin(collect))> {
  return { p, std::begin(collect), std::end(collect) };
}