If the custom code is generic and can be used in other projects, then putting it in a library may be a better option than a project specific second source folder.
如果定制代码是一般化的并被应用于其他项目，那么比起放入特定项目的次级源文件夹，将其放入库中是个更好的选择。
MF: I think AOP is an unconnected concept, other than in the generic sense that describing aspects with a DSL may be more readable than a framework's command-query interface.
MF： 我认为AOP是一个完全不同的概念，不过通常认为借助领域特定语言来描述横切问题应该比用普通框架的命令-查询式接口更具可读性。
For starters, arrays in Scala are effectively generic classes, with no "built-in" status accrued to them (at least, no more than any other class that ships with the Scala library).
对于新手，Scala中的数组实际上就是泛型类，没有增加“内置”状态(至少，不会比scala库附带的其他类多)。
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