A sealed class cannot be used as a base class.

密封类别不能当做基底类别使用。

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Because they can never be used as a base class, some run-time optimizations can make calling sealed class members slightly faster.

由于密封类从不用作基类，所以有些运行时优化可以使对密封类成员的调用略快。

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We'll learn one technique that helps when we discuss sealed class hierarchies in the section called "sealed class hierarchies" in Chapter 7, the Scala Object System.

我们会在《第7章- Scala对象系统》的“完成类(sealed class)结构”讨论完成类的结构时学习到其中一种技术。

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