sealed class

基本解释

A sealed class cannot be used as a base class.
密封類別不能儅做基底類別使用。
Because they can never be used as a base class, some run-time optimizations can make calling sealed class members slightly faster.
由於密封類從不用作基類，所以有些運行時優化可以使對密封類成員的調用略快。
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.
我們會在《第7章 - Scala 對象系統》的“完成類（sealed class）結搆”討論完成類的結搆時學習到其中一種技術。

In the end it was the halving of premium travel (supersonic, first class and business class) thanks to economic slow-down, terrorism and the Iraq war that sealed its fate.
ECONOMIST: Air travel: After Concorde The