//********************************************************
// The following code example is taken from the book
//  C++23 - The Complete Guide
//  by Nicolai M. Josuttis (www.josuttis.com)
//  https://www.cppstd23.com
//
// The code is licensed under a
//  Creative Commons Attribution 4.0 International License
//  https://creativecommons.org/licenses/by/4.0/
//********************************************************


#include <utility>
#include <ranges>

// new view type to process all elements:
template<std::ranges::input_range InnerRgT>
struct ProcessView : std::ranges::view_interface<ProcessView<InnerRgT>>
{
 private:
  InnerRgT innerRange;  // view, ref_view to range, or owning view to range
 public:
  template<std::ranges::range RgT>
  ProcessView(RgT&& rg) 
   : innerRange(std::forward<RgT>(rg)) {
  }
  auto begin() { return std::ranges::begin(innerRange); }
  auto end() { return std::ranges::end(innerRange); }
};

// deduction guide to deal with lvalues and rvalues:
template<std::ranges::range RgT> 
ProcessView(RgT&& rg) -> ProcessView<std::ranges::views::all_t<RgT>>;

// make the view usable in a pipeline:
struct ProcessViewFO : std::ranges::range_adaptor_closure<ProcessViewFO>
{
  template<std::ranges::input_range Rng>
  constexpr auto operator()(Rng&& rng) const {
      return ProcessView(std::forward<Rng>(rng));
  }
};
constexpr ProcessViewFO process{};  // for:  rg | process | ...