public void AwaitOnCompleted <TAwaiter, TStateMachine>(
            ref TAwaiter awaiter, ref TStateMachine stateMachine)
            where TAwaiter : INotifyCompletion
            where TStateMachine : IAsyncStateMachine
        {
            var foo = stateMachine;

            if (awaiter is IStepResultAwaiter stateAwaiter)
            {
                if (stateAwaiter.IsCompleted)
                {
                    awaiter.OnCompleted(() => { foo.MoveNext(); });
                }
                else
                {
                    Task = new StepState <T>(stateAwaiter.Data);
                }
            }
        }
 public void SetResult(T result) => Task = new StepState <T>(result);