cpp/thread/stop token/stop token

Constructs a new object.

@1@ Constructs an empty with no associated stop-state. @2@ Copy constructor. Constructs a whose associated stop-state is the same as that of. @3@ Move constructor. Constructs a whose associated stop-state is the same as that of ;  is left empty.

Postconditions
@1@ stop_possible and stop_requested are both @2@ and  share the same associated stop-state and compare equal @3@ has 's previously associated stop-state, and  is