Yield

Yield：是一个关键字，通过状态机实现，充分体现了延迟加载的特性。
下面是一个实例代码，运行一下，会发现Yield的神奇之处。

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($"获取{counter}次数据");
                result = 2 * result;
                results.Add(result);
            }
            return results;
        }
        public static IEnumerable<int> YieldMethod()
        {
            int counter = 0;
            int result = 1;
            while (counter++ < 10)
            {
                Thread.Sleep(1000);
                Console.WriteLine($"获取{counter}次数据");
                result = 2 * result;
                yield return result;
            }
        }
    }