关于拉姆达表达式的疑问

  public class LambdaTest
    {

        static void Main()
        {
            var counter = 0;
            WriteStream(() => counter++);
            Console.WriteLine("Final value of counter: {0}", counter);

        }
        static void WriteStream(Func<int> counter)
        {
            for (var i = 0; i < 10; ++i)
            {
                Console.WriteLine("{0}, ", counter());
            }
        }
    }
}