Function start

include/exec/async_scope.hpp:398–419

      }

      constexpr void start() & noexcept
      {
        STDEXEC_TRY
        {
          if (!!__state_)
          {
            std::unique_lock __guard{__state_->__mutex_};
            if (__state_->__data_.index() != 0)
            {
              __guard.unlock();
              __complete_();
            }
            else
            {
              __state_->__subscribers_.push_back(this);
            }
          }
        }
        STDEXEC_CATCH_ALL
        {
          STDEXEC::set_error(static_cast<_Receiver&&>(__rcvr_), std::current_exception());
        }
      }
    };