Function make_stop_callback

test/stdexec/algos/adaptors/test_stop_when.cpp:82–91

  template <std::invocable Fn>
  ex::sender auto make_stop_callback(Fn&& fn) noexcept
  {
    return ex::read_env(ex::get_stop_token)
         | ex::then(
             [fn = std::forward<Fn>(fn)](auto token) mutable noexcept
             {
               using cb_t = decltype(token)::template callback_type<std::remove_cvref_t<Fn>>;
               return std::optional<cb_t>(std::in_place, std::move(token), std::move(fn));
             });
  }

  TEST_CASE("callbacks registered with stop-when's token can be invoked", "[adaptors][stop-when]")
  {