cpp-lazy-stream/streams/map.hpp

#pragma once

namespace stream { namespace detail {
  namespace map {
    template <typename T, typename R>
    class iterator {
    public:
      iterator(std::function<R(T const&)> f, ::stream::iterator<T>&& impl)
      : fun_(f), impl_(std::forward<::stream::iterator<T>>(impl)) {}

      R operator*() { return fun_(*impl_); }
      DELEGATE_ITERATOR_IMPL(impl_)
    private:
      std::function<R(T const&)> fun_;
      ::stream::iterator<T> impl_;
    };
  }
  
  template <typename T, typename R>
  class map_stream : public stream_impl<R> {
  public:
    template <typename F>
    map_stream(F&& func, stream_base<T> const& sb) : fun_(func), source_(sb) {}
    ~map_stream() override {}
    
    iterator<R> begin() override {
      return {map::iterator<T, R>{fun_, source_.begin()}};
    }
    
    iterator<R> end() override {
      return {map::iterator<T, R>{fun_, source_.end()}};
    }
  private:
    std::function<R(T const&)> fun_;
    stream_base<T> source_;
  };
  
  template <typename T>
  template <typename F>
  auto stream_base<T>::map(F&& func) const -> stream_base<map_f<F>> {
    using impl_t = map_stream<T, map_f<F>>;
    return {std::make_shared<impl_t>(func, *this)};
  }
} }