不可变数据是许多侧重于并发性的语言的关键方面，因为它有如此好的属性。
Immutable data is a key aspect of many languages that focus on concurrency because it has such nice properties.
列举型别可视为是资料型别，您可以用来建立多组常数以便与变数和属性搭配使用。
Enumerations are treated as data types, and you can use them to create sets of constants for use with variables and properties.
下表会显示变数和属性间的一些重要差异点。
The following table shows some important differences between variables and properties.
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