还可以看到，when关键词定义规则中的条件块，then关键词定义结果块。

You can also see that the when keyword defines the conditional part of a rule, and the then keyword defines the consequence part.

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接下来，UnitsConverter也是一个单例模式，因为它是使用object关键词定义的。

Next, UnitsConverter is also a singleton as it is defined using the object keyword.

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定义中最后一个关键词是帮助。

The last keyword in the definition is assist.

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