何时在Dart中使用零件/零件与导入/导出？ [英] When to use part/part of versus import/export in Dart?

问题描述

我不完全理解的部分 / 部分和导入 / export 在Dart中使用库时。例如：

I do not completely understand the difference between part/part of and import/export when using libraries in Dart. For example:

one.dart:
library one;
part "two.dart";
Class One {
};

和

two.dart:
part of one;
import 'somefile.dart';
Class Two {
}

对比

library one;
import 'two.dart';
Class One {
}

和

library two;
import 'somefile.dart';
export 'somefile.dart';
Class Two {
}

两种情况似乎都做同样的事情。什么时候使用的部分和部分而不是导入？还有在某些情况下导入不起作用，但是部分和部分会吗？

Both scenarios seem to do the same thing. When is it advantageous to use part and part of rather than import? And are there scenarios where import will not work, but part and part of will?

推荐答案

更新2018/03

部分和部分用于代码生成方案（而不是

part and part of is used more and more for code generation scenarios recently (instead of deprecated transformers) and unlikely to go away anytime soon.

像 built_value ， json_serializable之类的软件包，还有许多其他依赖于此的文件。

Packages like built_value, json_serializable, and many others depend on it.

只有通过将软件包中的所有文件捆绑到一个库中，Discouraged才是这样一个库文件，所有其他文件都属于该库。

Discouraged is only the patter where all files of a package are tied together to a single library by having one library file and all other files being part of that library.

原始

在Dart中，可以在同一库中访问私有成员。使用导入，您可以导入库，并且只能访问其公共成员。使用部分 / 部分的一部分，您可以将一个库分成几个文件，并且私有成员可访问这些文件中的所有代码。

In Dart, private members are accessible within the same library. With import you import a library and can access only its public members. With part/part of you can split one library into several files and private members are accessible for all code within these files.

请参阅以上更新中对以下段落的说明

使用<$ c $建议不要使用中的c>部分 / 部分，Dart团队正在考虑摆脱它。我以为他们会介绍类似朋友（ https://github.com/dart- lang / sdk / issues / 22841 ），其中两个图书馆在终止 part / part之前可以互访对方的私有成员。的（可能在将来的Dart版本中）。

Using part / part of is discouraged and the Dart team is considering getting rid of it. I assume they will introduce something like "friend" (https://github.com/dart-lang/sdk/issues/22841), where two libraries can access each other's private members as an alternative before they discontinue part / part of (maybe in a future Dart version).

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