It calls the primary constructor with Nil (which represents an empty List object).

它调用主构造函数，并且传入Nil (Nil表示了一个空的List对象)。

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Scala distinguishes between a primary constructor and zero or more auxiliary constructors.

Scala可以区分主构造函数和0个或多个辅助构造函数。

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Traits don't support auxiliary constructors, nor do they accept an argument list for the primary constructor, the body of a trait.

Traits不支持辅助构造函数，它们也不支持在主构造函数，trait的主体里的参数列表。

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