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定义运算符==时，空值返回“调用不明确”

[英]When defining the operator ==, null value returns “call is ambiguous”

原文 2013-05-17 04:59:53 3 3 c#/ null/ call/ operator-keyword/ ambiguous

I have custom classes Rational, Real, and Complex. 我有自定义类Rational，Real和Complex。 In Complex I overload operators that allow me to compare a Complex and a Real, or a Complex and a Rational. 在Complex中，重载运算符使我可以比较Complex和Real，或者Complex和Rational。 It would be easy if I could define an implicit cast of a Rational to a Complex, say, but for reasons not worth going into, I can't. 如果我可以定义从Rational到Complex的隐式转换，这很容易，但是由于不值得深入探讨的原因，我做不到。

Therefore I have, among others, 因此，除其他外，我有

==(Complex a, Real b)

and also 并且

==(Real a, Complex b)

Obviously when I try to compare 显然，当我尝试比较时

c==null

I get the error message that the call is ambiguous. 我收到错误消息，该呼叫是模棱两可的。 I saw on a related thread the idea that I could just define ==(Complex a, object b) I had thought of that, but then if I want to allow symmetry, I also need ==(object a, Complex b) in which case a comparison between two complexes will also be ambiguous. 我在一个相关的线程上看到了我可以定义==(Complex a, object b)想法，但是如果我想允许对称，我还需要在其中==(object a, Complex b)在这种情况下，两个复合体之间的比较也将是模棱两可的。

Right now when I check for null I'm having to cast the Complex to an object first. 现在，当我检查null时，我必须首先将Complex转换为对象。 What's a better solution? 有什么更好的解决方案？ (I'm hoping for a general solution rather than a solution that depends on any relationship between the classes eg inheritance.) （我希望有一个通用的解决方案，而不是依赖于类之间任何关系（例如继承）的解决方案。）

3 个解决方案

Why to use the second overload? 为什么要使用第二个过载？ Are you sure you cannot use first one for your checks? 您确定不能使用第一个支票吗？ There is no "good-looking" solution you are looking for. 您没有正在寻找的“好看”解决方案。

我认为您有==(Complex c, Real C)和==(Complex c, Complex C) ，当然编译器不会知道选择哪个，因此当您与null比较时，您必须像c1 == (Complex) null 。

I should probably post that I don't think there is a solution, and I just decided to forsake symmetry and go with ==(Complex a, object b). 我可能应该发贴说我不认为有解决方案，我只是决定放弃对称性，并使用==（Complex a，object b）。 Thanks to everyone who posted! 感谢所有张贴的人！