std::nostopstate_t
From cppreference.com
                    
                                        
                    < cpp | thread | stop source
                    
                                                            
                    |   Defined in header  <stop_token>
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|   struct nostopstate_t {     explicit nostopstate_t() = default;  | 
(since C++20) | |
Unit type intended for use as a placeholder in std::stop_source non-default constructor, that makes the constructed std::stop_source empty with no associated stop-state.