对于普通的参数来说，这样做没有什么必要，它也很难通过闭包来确保可用性。
While doing this is trivial for normal parameters, it is very hard to make that guarantee with a closure.
对于像源文件或包这样的构件也可以直接删除。
Deleting artifacts such as source files or packages is again straightforward.
对于将用例图中的参与者转换成类图中有效的抽象，镜像映象模式和会话虚包模式是很有用的，这样最终将能够更清楚地转换成代码。
The Mirror Image and Session Facade patterns are useful for changing actors in use case diagrams into valid abstractions in class diagrams, which ultimately results in a cleaner translation to code.
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