void.h

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// SPDX-License-Identifier: BSD-3-Clause
#ifndef TTG_VOID_H
#define TTG_VOID_H
#include <iostream>
#include "ttg/util/meta.h"
 
namespace ttg {
 
  class Void {
  public:
    Void() = default;
    template <typename T> explicit Void(T&&) {}
  };
 
  inline bool operator==(const Void&, const Void&) { return true; }
  inline bool operator!=(const Void&, const Void&) { return false; }
 
  inline std::ostream& operator<<(std::ostream& os, const ttg::Void&) {
    return os;
  }
 
  static_assert(meta::is_empty_tuple_v<std::tuple<>>,"ouch");
  static_assert(meta::is_empty_tuple_v<std::tuple<Void>>,"ouch");
 
  namespace detail {
 
    template<std::size_t... Is>
    auto make_void_tuple(std::index_sequence<Is...>) {
      auto g = [](int i){ return Void{}; };
      return std::make_tuple(g(Is)...);
    }
 
    template<std::size_t N>
    auto make_void_tuple() {
      return make_void_tuple(std::make_index_sequence<N>{});
    }
 
  } // namespace detail
 
}  // namespace ttg
 
namespace std {
  template <>
  struct hash<ttg::Void> {
    template <typename ... Args> int64_t operator()(Args&& ... args) const { return 0; }
  };
} // namespace std
 
#endif // TTG_VOID_H