Dart中的patch关键字有什么作用？ [英] What does the patch keyword in Dart do?

问题描述

有人可以解释patch关键字的作用吗？例如，在
math_patch.dart 中，我看到

Can someone explain what the patch keyword does? For example, in math_patch.dart I see

patch num pow(num x, num exponent) => MathNatives.pow(x, exponent);
patch double atan2(num a, num b) => MathNatives.atan2(a, b);
patch double sin(num x) => MathNatives.sin(x);
patch double cos(num x) => MathNatives.cos(x);

这是什么意思？ _patch.dart 文件有什么用途？

What does this mean? What are _patch.dart files for?

推荐答案

修补程序机制是在内部使用（并且仅供内部
使用，不适用于最终用户）以提供
核心库功能的不同实现。

The patch mechanism is used internally (and is only available internally, not to end users) to provide different implementations of core library functionality.

对于数学库如下所示， lib / math 中与平台无关的
库源将这些方法声明为 external 。
external 方法是从补丁文件获取其实现的。
是VM中 runtime / lib / math_patch.dart 中的补丁文件，其中
提供了实现VM和
中的补丁文件
中的 dart2js 编译器在
lib / compiler / implementation / lib / math_patch中。 dart ，它提供
dart2js 实现。

For the math library that you have below, the platform independent library source in lib/math declares these methods as external. external methods get their implementation from a patch file. There is a patch file in the VM in runtime/lib/math_patch.dart, which supplies the implementation for the VM and there is a patch file in the dart2js compiler in lib/compiler/implementation/lib/math_patch.dart, which supplies the dart2js implementation.

The <$分析器可以理解c $ c> external 关键字，并且这种
方式只能将共享部分包含在SDK中，而
工具可以理解。这意味着SDK可以具有 lib / math ，而不是
lib / math / runtime 和 lib / math / dart2js ，这使SDK更加整洁，并使
更易于理解。

The external keyword is understood by the analyzer and doing it this way allows only the shared part to be in the SDK and be understood by the tools. That means that the SDK can have lib/math instead of having lib/math/runtime and lib/math/dart2js, which makes the SDK cleaner and easier to understand.

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