我注意到通用的IEnumerator<T>继承自 IDisposable，但非泛型接口 IEnumerator 则不继承。为什么要这样设计呢？
通常，我们使用foreach语句来遍历IEnumerator<T>实例。 foreach 的生成代码实际上有一个 try-finally 块，它在 finally 中调用 Dispose() 。
Basically it was an oversight. In C# 1.0, foreach never called Dispose 1. With C# 1.2 (introduced in VS2003 - there's no 1.1, bizarrely) foreach began to check in the finally block whether or not the iterator implemented IDisposable - they had to do it that way, because retrospectively making IEnumerator extend IDisposable would have broken everyone's implementation of IEnumerator. If they'd worked out that it's useful for foreach to dispose of iterators in the first place, I'm sure IEnumerator would have extended IDisposable.
然而，当 C# 2.0 和 .NET 2.0 出现时，它们有了一个新的机会——新的接口、新的继承。扩展接口更有意义IDisposable这样你就不需要在finally块中进行执行时检查，现在编译器知道迭代器是否是一个IEnumerator<T>它可以发出无条件调用Dispose.
编辑：这对于Dispose在迭代结束时调用（无论如何结束）。这意味着迭代器可以保留资源 - 这使得它可以逐行读取文件。迭代器块生成Dispose确保任何实施finally与迭代器的“当前执行点”相关的块在其被释放时执行 - 因此您可以在迭代器中编写正常的代码，并且应该适当地进行清理。
1 Looking back at the 1.0 spec, it was already specified. I haven't yet been able to verify this earlier statement that the 1.0 implementation didn't call Dispose.
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