可以证明，对于高度可重用的服务层来说，添加新的最终用户功能和修改现有的功能要简单得多。

Adding new end-user features and modifying existing ones can prove much simpler with a highly reusable service layer.

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虽然对于一个打开文件的简单例子来说，这些额外的复杂操作似乎还是比较合理，但当你添加更多功能和更进一步的异步读取能力到应用程序中的时候，你不久就会麻烦不断了。

While these extra complications seem reasonable for a simple example like opening a file you soon run into problems as you add more functionality and further asynchronous reads to the application.

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