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

#pragma once

#include <memory>

#include "source.hpp"

namespace stream {
  /**
   * Construct a stream out of the given container. If C && is an rvalue
   * reference, the returned object will take ownership of cont. Otherwise, we
   * capture cont by reference to maximise performance.
   */
  template <typename C>
  auto make_stream(C && cont) -> detail::stream_base<decltype(*cont.begin())> {
    return std::make_shared<detail::source_stream<C>>(std::forward<C>(cont));
  }

  template <typename T> detail::stream_base<T &> make_empty_stream() {
    return std::make_shared<detail::range_stream<T *, T &>>(nullptr, nullptr);
  }

  /**
   * Construct a single element stream containing the pointer given
   */
  template <typename T> detail::stream_base<T &> make_stream(T * ptr) {
    return std::make_shared<detail::range_stream<T *, T &>>(ptr, ptr + 1);
  }

  /**
   * Construct a stream from input iterators representing the start and end
   * Requirements: It must be an iterator type that provides the trait
   * 'reference'
   */
  template <typename It>
  detail::stream_base<typename It::reference> make_stream(It begin, It end) {
    return std::make_shared<detail::range_stream<It>>(begin, end);
  }

  /**
   * Construct a stream given certain start and end bounds.
   * e.g. stream::make_range_stream(0, 10)
   */
  template <typename T>
  detail::stream_base<T &> make_range_stream(T start, T const & end) {
    std::vector<T> vec;
    vec.reserve(end - start);
    while (start < end) {
      vec.emplace_back(start++);
    }
    return make_stream(std::move(vec));
  }

  /**
   * Construct a stream given certain start and end bounds, as well as an
   * increment amount. e.g. stream::make_range_stream(0, 10, 2)
   */
  template <typename T>
  detail::stream_base<T &> make_range_stream(T start, T const & end,
                                             T const & increment) {
    int elems{(end - start) / increment};
    if (elems < 0 || end == start) { return {}; }
    std::vector<T> vec{start};
    vec.reserve(elems + 1);
    while (elems-- > 0) {
      vec.emplace_back(start += increment);
    }
    return make_stream(std::move(vec));
  }
}