在Flow中使用星号（*）类型有什么用，在TypeScript中有什么用呢？ [英] What is the use of asterisk (*) type in Flow and what is the equivalent of that in TypeScript?

问题描述

首先，我大多熟悉TypeScript。 Flow在许多方面看起来与TS非常相似，但我最近偶然发现了一个星号（*）类型。起初，我认为它是any的同义词，但是现在，在阅读了Flow的一些发行说明后，我发现它并非如此。我浏览了所有官方文档，但未能找到*的任何用法。

First of all, I am mostly familiar with TypeScript. Flow looks very similar to TS in many ways, but I recently stumbled upon an asterisk (*) type. At first, I thought it was a synonym for "any", but now, after reading some of the release notes for Flow, I see that it's not. I skimmed through all the official docs and was not able to find any usage of "*".

那么，它是什么以及何时使用它？但是，什么是TypeScript中的直接等价？

So, what is it and when to use it? But also, what would be a direct equivalent of that in TypeScript?

推荐答案

编辑：因为我最初写这个答案，我有据悉， * 出现在模块边界时是不安全的。我不建议使用它，它可能会在将来被删除。

Since I originally wrote this answer, I have learned that * is unsafe when it appears at module boundaries. I can't recommend using it, and it may be removed in the future.

它只是告诉Flow推断一个类型参数，而不是让你明确地写出来：

It just tells Flow to infer a type parameter, rather than making you write it out explicitly:

function foo(): Array<*> {
  return [5];
}

// Flow issues an error:
//    2:   return [5];
//                 ^ number. This type is incompatible with
//    10: (foo(): Array<string>);
//                     ^ string
(foo(): Array<string>);

（尝试流程）

它不同于任何 - - 任何都是不安全的类型，所以如果用替换 * 任何在这个例子中，Flow不会给你任何错误。你可以用 number 替换它，Flow会给你一个类似的错误。

It is different from any -- any is an unsafe type, so if you replaced * with any in this example, Flow would not give you any errors. You could replace it with number and Flow would give you a similar error.

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