好，我们从这个非常简单的按钮点击方法开始
private void button1_Click(object sender, EventArgs e)
{
int counter = 1;
List<int> items = new int[] { 1, 2, 3 }.ToList();
List<int>.Enumerator enm = items.GetEnumerator();
// 1
if (!enm.MoveNext())
throw new Exception("Unexpected end of list");
if (enm.Current != counter)
throw new Exception(String.Format("Expect {0} but actual {1}", counter, enm.Current));
counter++;
// 2
if (!enm.MoveNext())
throw new Exception("Unexpected end of list");
if (enm.Current != counter)
throw new Exception(String.Format("Expect {0} but actual {1}", counter, enm.Current));
counter++;
//3
if (!enm.MoveNext())
throw new Exception("Unexpected end of list");
if (enm.Current != counter)
throw new Exception(String.Format("Expect {0} but actual {1}", counter, enm.Current));
counter++;
if (enm.MoveNext())
throw new Exception("Unexpected continuation of list");
}
这个方法什么都不做，因为每个断言都优雅地通过了。一切都很好，直到我相信我应该介绍一种消除冗余的方法
static void AssertNext(ref int counter, List<int>.Enumerator e)
{
if (!e.MoveNext())
throw new Exception("Unexpected end of list");
if (e.Current != counter)
throw new Exception(String.Format("Expect {0} but actual {1}", counter, e.Current));
counter++;
}
private void button2_Click(object sender, EventArgs e)
{
var counter = 1;
var items = new int[] { 1, 2, 3 }.ToList();
var enm = items.GetEnumerator();
AssertNext(ref counter, enm);
AssertNext(ref counter, enm);
AssertNext(ref counter, enm);
if (enm.MoveNext()) throw new Exception("Unexpected continuation of list");
}
尽管如此，这种重构还是很简单的（至少对我而言）。它确实破坏了程序！在第二次调用 AssertNext 时，似乎枚举器已经重置到起点并导致断言失败。
我无法理解发生了什么。我真的觉得自己是这个谜题的初学者。
我在这里想念什么？