扩展通过继承枚举 [英] Extending an enum via inheritance

问题描述

我知道这相当不利于枚举的想法，但有可能延长枚举在C＃/ Java的？在增加新的价值，以枚举双方的意义上，我的意思是扩展，而且在从现有的枚举继承的面向对象的意义。

I know this rather goes against the idea of enums, but is it possible to extend enums in C#/Java? I mean "extend" in both the sense of adding new values to an enum, but also in the OO sense of inheriting from an existing enum.

我想这是不可能在Java中，因为它仅得到了他们相当最近（Java 5的？）。 C＃似乎更宽容的人希望做疯狂的事情，虽然如此，我认为这是可能的一些方法。 presumably它可以通过反射被黑客攻击了（不是说你所有的实际使用该方法）？

I assume it's not possible in Java, as it only got them fairly recently (Java 5?). C# seems more forgiving of people that want to do crazy things, though, so I thought it might be possible some way. Presumably it could be hacked up via reflection (not that you'd every actually use that method)?

我并不感兴趣，在实施任何给定的方法，它只是受到挑衅时，我想到了我的好奇： - ）

I'm not necessarily interested in implementing any given method, it just provoked my curiosity when it occurred to me :-)

推荐答案

您不能扩展枚举的原因是因为它会导致问题的多态性。

The reason you can't extend Enums is because it would lead to problems with polymorphism.

假设你有一个枚举MyEnum与值A，B和C，并与值D为MyExtEnum扩展它。

Say you have an enum MyEnum with values A, B, and C , and extend it with value D as MyExtEnum.

假设一个方法需要一个myEnum价值的地方，例如作为一个参数。它应该是合法的供应MyExtEnum的价值，因为它是一个亚型，但现在你有什么打算这样做，当它原来的价值为D？

Suppose a method expects a myEnum value somewhere, for instance as a parameter. It should be legal to supply a MyExtEnum value, because it's a subtype, but now what are you going to do when it turns out the value is D?

要解决这个问题，扩展枚举是非法的。

To eliminate this problem, extending enums is illegal

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