如何解释这些 TypeScript 声明中的 [p in keyof T] 和 T[p]? [英] How to interpret [p in keyof T] and T[p] in these TypeScript declarations?

问题描述

我正在阅读 ngrx 文档并偶然发现了这样的代码.[p in keyof T] 和 T[p] 是什么意思?

I am reading ngrx docs and stumbled upon such a code. What do [p in keyof T] and T[p] mean?

export type ActionReducerMap<T, V extends Action = Action> = {
  [p in keyof T]: ActionReducer<T[p], V>
};

推荐答案

那是映射类型.您可以在打字稿文档此处中或在此博文.

That is a mapped type. You can read about them in the typescript docs here, or in this blog post.

基本上，语法 [p in keyof T] 就是这个意思；p 是对象T 的键之一.然后，T[p] 只表示该键值的类型.阅读这两个链接以获得更可靠的解释.

Basically, the syntax [p in keyof T] means just that; p is one of the keys of the object T. Then, the T[p] just represents the type of that key's value. Read those two links for a more robust explanation.

这篇关于如何解释这些 TypeScript 声明中的 [p in keyof T] 和 T[p]?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！