Yield

Yield：是一個關鍵字，通過狀態機實現，充分體現了延遲加載的特性。
下面是一個實例代碼，運行一下，會發現Yield的神奇之處。

class Program
    {
        static void Main(string[] args)
        {
            {
                IEnumerable<int> results = CommonMethod();
                results = YieldMethod();
            }
            Console.WriteLine("*******************************");
            {
                IEnumerable<int> results = CommonMethod();
                foreach (var item in results)
                {
                    Console.WriteLine(item);
                }
            }
            Console.WriteLine("*******************************");
            {
                IEnumerable<int> results = YieldMethod();
                foreach (var item in results)
                {
                    Console.WriteLine(item);
                }
            }
            Console.ReadKey();
        }

        public static IEnumerable<int> CommonMethod()
        {
            List<int> results = new List<int>();
            int counter = 0;
            int result = 1;
            while (counter++ < 10)
            {
                Thread.Sleep(1000);
                Console.WriteLine($"獲取{counter}次數據");
                result = 2 * result;
                results.Add(result);
            }
            return results;
        }
        public static IEnumerable<int> YieldMethod()
        {
            int counter = 0;
            int result = 1;
            while (counter++ < 10)
            {
                Thread.Sleep(1000);
                Console.WriteLine($"獲取{counter}次數據");
                result = 2 * result;
                yield return result;
            }
        }
    }