cpp-lazy-stream/include/stream/filter.hpp

#pragma once

#include <stream/iterator.hpp>

#include <iterator/filter_iterator.hpp>

namespace stream::detail {
template <typename T> class filter_stream {
public:
  using iter_type = ::iterator::filter_iterator<iterator<T>, true>;

public:
  template <typename F>
  filter_stream(F && func, stream_base<T> const & sb)
      : pred_(func), source_(sb) {}

  iterator<T> begin() { return iter_type(pred_, source_); }
  iterator<T> end() { return iter_type(); }

private:
  typename iter_type::predicate_t pred_;
  stream_base<T> source_;
};

template <typename T>
template <typename F>
auto stream_base<T>::filter(F && pred) && -> stream_base<T> {
  return std::make_shared<filter_stream<T>>(pred, std::move(*this));
}

template <typename T>
template <typename F>
auto stream_base<T>::filter(F && pred) const & -> stream_base<T> {
  return std::make_shared<filter_stream<T>>(pred, *this);
}
}