cpp-lazy-stream/include/stream/streams/self_iterating_contianer.hpp

#pragma once

namespace stream { namespace detail {
  template <typename C, typename It = typename C::const_iterator>
  class self_iterating_container {
  private:
    std::ptrdiff_t offset{0};
    C container;
    It current;
    It end;

  public:
    self_iterating_container() = default;
    self_iterating_container(C const & container)
        : container(container), current(container.cbegin()),
          end(container.cend()) {}

    self_iterating_container(C && container)
        : container(std::move(container)), current(container.cbegin()),
          end(container.cend()) {}

    self_iterating_container(self_iterating_container const & other) {
      *this = other;
    }

    self_iterating_container(self_iterating_container && other) {
      *this = std::move(other);
    }

    self_iterating_container &
    operator=(self_iterating_container const & other) {
      offset = other.offset;
      container = other.container;
      setup();
      return *this;
    }

    self_iterating_container & operator=(self_iterating_container && other) {
      offset = other.offset;
      container = std::move(other.container);
      setup();
      return *this;
    }

    void operator++() {
      ++offset;
      ++current;
    }
    auto & operator*() const { return *current; }
    operator bool() const { return current != end; }

  private:
    void setup() {
      current = container.cbegin();
      end = container.cend();
      std::advance(current, offset);
    }
  };
}}