c# - 枚举中相等运算符和运算符之间的区别

Question

给定以下枚举，

enum ExampleOptions
{
  OptionA,
  OptionB
}

这两种说法有什么真正的区别吗？

ExampleOptions option = ExampleOptions.OptionA;

bool equals1 = option == ExampleOptions.OptionA; // true
bool equals2 = option is ExampleOptions.OptionA; // true

据我所知，使用 == 和 is 之间的唯一区别主要是 is 需要一个常量操作数(因此, 操作顺序很重要)。

I used to use the == operator just because I wanted to avoid ugly statements such as
!(option is ExampleOptions.OptionA).
But, after C#9 was released and the is not operator added; I find is/is not a cleaner and more verbose way to write this kind of statements.

决定使用哪个运算符是否有任何隐藏的后果？

Answer 1

As far as I can see, the only difference between using == and is is mainly that is expects a constant operand (thus, operation order matters).

还有很多不同之处，例如 is 允许您编写如下语句:

val is ExampleOptions.OptionA or ExampleOptions.OptionB or ExampleOptions.OptionD

而不是使用 || 并重复命名变量的老式语句。

is 也(这很重要!)不调用 operator ==，它直接检查实例。这不适用于枚举，但如果您的对象具有用户定义的 == 运算符且不检查 null，var != null 很可能会因异常而崩溃，而 var is not null 会如您所愿。