text: // include/p2300/start.hpp                                            -*-C++-*-
  // ----------------------------------------------------------------------------
  //  Copyright (C) 2022 Dietmar Kuehl http://www.dietmar-kuehl.de
  //
  //  Permission is hereby granted, free of charge, to any person
  //  obtaining a copy of this software and associated documentation
  //  files (the "Software"), to deal in the Software without restriction,
  //  including without limitation the rights to use, copy, modify,
  //  merge, publish, distribute, sublicense, and/or sell copies of
  //  the Software, and to permit persons to whom the Software is
  //  furnished to do so, subject to the following conditions:
  //
  //  The above copyright notice and this permission notice shall be
  //  included in all copies or substantial portions of the Software.
  //
  //  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  //  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  //  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  //  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  //  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  //  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  //  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  //  OTHER DEALINGS IN THE SOFTWARE.
  // ----------------------------------------------------------------------------
  
  #ifndef INCLUDED_INCLUDE_P2300_START
  #define INCLUDED_INCLUDE_P2300_START
  
  #include <functional.hpp>
  #include <type_traits>
  
  // ----------------------------------------------------------------------------
  // [exec.op_state.start]
  
  namespace std {
      namespace _Start {
          class _Cpo {
          public:
              template <class _OperationState>
                  requires nothrow_tag_invocable<_Cpo, _OperationState>
                      && std::is_lvalue_reference_v<_OperationState>
              auto operator()(_OperationState&& __state) const noexcept -> void
              {
                  tag_invoke(*this, __state);
              }
          };
      }
  
      namespace execution {
          using start_t = _Start::_Cpo;
          inline namespace _Cpos {
              inline constexpr start_t start{};
          }
      }
  }
  
  // ----------------------------------------------------------------------------
  
  #endif
  