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);
  }
};
}}