A fundamental design precept is that a class should be part of a domain package only if it exists to fulfill the goals of that domain package.
一个基本的设计规则就是，一个类只要存在并去完成一个域包的目标，那么它就应该是该域包的一部分。
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Given that the only fundamental difference between them is the name of the class, it would help to have a simple way to create a template for a single rule that handles all cases.