Well-known object types can be either single call or singleton.

已知物件型别可以是单一呼叫或单一物件。

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We could either implement each state as a Singleton, or create a factory of states which creates and manages the states.

我们既可以执行每个状态作为 Singleton，也可以创建一个状态工厂用于生成和管理状态。

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Users of the class can then add and remove Attendee elements from the collection the Singleton instance holds, or replace the elements in the collection.

然后，该类的用户可以在 Singleton 实例保存的集合中添加和删除 Attendee 元素，或替换集合中的元素。

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"Anything more than a singleton or twins is risky, " Miller says.

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