Асинхронное программирование, метод Task.Run() для случая создания задачи с получением результата

         static int Factorial(int n)
        {
            int result = 1;
            for (int i = 1; i <= n; i++)
            {
                result *= i;
            }
            return result;
        }
        // определение асинхронного метода
        static async void FactorialAsync(int n)
        {
            int x = await Task.Run(()=>Factorial(n));
            Console.WriteLine($"Факториал равен {x}");
        }

        public static Task<TResult> Run<TResult>(Func<TResult> function)
        {
            return Task<TResult>.StartNew(null, function, default,
                TaskCreationOptions.DenyChildAttach, InternalTaskOptions.None, TaskScheduler.Default);
        }

        internal static Task<TResult> StartNew(Task? parent, Func<TResult> function, CancellationToken cancellationToken,
            TaskCreationOptions creationOptions, InternalTaskOptions internalOptions, TaskScheduler scheduler)
        {
            if (function == null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.function);
            }
            if (scheduler == null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.scheduler);
            }
 
            // Create and schedule the future.
            Task<TResult> f = new Task<TResult>(function, parent, cancellationToken, creationOptions, internalOptions | InternalTaskOptions.QueuedByRuntime, scheduler);
 
            f.ScheduleAndStart(false);
            return f;
        }

        internal Task(Func<TResult> valueSelector, Task? parent, CancellationToken cancellationToken,
            TaskCreationOptions creationOptions, InternalTaskOptions internalOptions, TaskScheduler? scheduler) :
            base(valueSelector, null, parent, cancellationToken, creationOptions, internalOptions, scheduler)
        {
        }

        internal Task(Delegate action, object? state, Task? parent, CancellationToken cancellationToken,
            TaskCreationOptions creationOptions, InternalTaskOptions internalOptions, TaskScheduler? scheduler)
        {
            if (action == null)
            {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.action);
            }
 
            // Keep a link to the parent if attached
            if (parent != null && (creationOptions & TaskCreationOptions.AttachedToParent) != 0)
            {
                EnsureContingentPropertiesInitializedUnsafe().m_parent = parent;
            }
 
            TaskConstructorCore(action, state, cancellationToken, creationOptions, internalOptions, scheduler);
 
            Debug.Assert(m_contingentProperties == null || m_contingentProperties.m_capturedContext == null,
                "Captured an ExecutionContext when one was already captured.");
            CapturedContext = ExecutionContext.Capture();
        }

        internal void TaskConstructorCore(Delegate? action, object? state, CancellationToken cancellationToken,
            TaskCreationOptions creationOptions, InternalTaskOptions internalOptions, TaskScheduler? scheduler)
        {
            m_action = action;
            m_stateObject = state;
            m_taskScheduler = scheduler;
//...

        internal virtual void InnerInvoke()
        {
            // Invoke the delegate
            Debug.Assert(m_action != null, "Null action in InnerInvoke()");
            if (m_action is Action action)
            {
                action();
                return;
            }
 
            if (m_action is Action<object?> actionWithState)
            {
                actionWithState(m_stateObject);
                return;
            }
            Debug.Fail("Invalid m_action in Task");
        }