为什么单例会违反开/关原则？ [英] Why singleton breaks open/closed principle?

问题描述

谁能告诉我为什么单例打破开放/封闭原则？
是因为从该类继承可能存在问题吗？

Could anyone tell me why does singleton break open/closed principle? Is it because there could be problems with inheriting from that class?

推荐答案

要使一个类开放必须有可能从中继承。继承是是关系。如果您从单例类继承，则子类的实例由于 is-a关系也将成为父类的实例，这意味着您可能突然拥有单例类的多个实例。

For a class to be "open" it must be possible to inherit from it. Inheritance is an "is-a" relationship. If you inherit from a singleton-class then instances of the child-class are also instances of the parent class due to the "is-a" relationship, meaning you can suddenly have multiple instances of the singleton class.

如果单例类禁止继承，则不再开放。

If the singleton class inhibits inheritance, it's no longer "open".

如果单例类允许继承且为开放进行扩展，则它不再可以强制执行单例模式。

If a singleton class allows inheritance, and is "open" for extension, then it can no longer enforce the singleton pattern.

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