然后，可以将每个指定的值看作是那个类的一个实例，这为您提供了指定的整数集合所无法提供的编译时类型安全。

You can then treat each named value as an instance of that class, providing you with compile-time type safety that a named set of integers can't.

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如果客户端代码尝试使用某个约束所不允许的类型来实例化类，则会产生编译时错误。

If client code tries to instantiate your class by using a type that is not allowed by a constraint, the result is a compile-time error.

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