键和值相同的对象的类型

问题描述

在打字稿中是否有一种方法可以表达一个函数的类型，该函数接受一个字符串列表，并创建一个对象，其中每个键的值都是键本身:

Is there a way in typescript to express the typings of a function that takes in a list of strings, and creates an object where each key's value is the key itself:

const createActionTypes = (types: string[]) => {
  return types.reduce((typesMap, type) => {
    typesMap[type] = type
    return typesMap
  }, {})
}

// Input
createActionTypes(['a', 'b'])

// Output
{ a: 'a', b: 'b' }

这是我尝试过的，但没有运气:

Here's what I've tried, without luck:

const createActionTypes = <T extends readonly string[], U extends T[number]>(
  types: T
): { [key in U]: U } => {
  return types.reduce((typesMap, type) => {
    typesMap[type] = type
    return typesMap
  }, {})
}

const x = createActionTypes(['a', 'b'] as const)
// Typings for x get resolved to: 
{
  a: "a" | "b";
  b: "a" | "b";
}

推荐答案

你真的很亲近.您需要指定该值与 key 的类型相同，而不是整个 "a"|"b" 即 U.

You are really close. You need to specify that the value is same type as key and not the whole set "a"|"b" which is U.

TS 游乐场链接

const createActionTypes = <T extends readonly string[], U extends T[number]>(
  types: T
): { [key in U]: key } => {
  return types.reduce((typesMap, type) => {
    typesMap[type] = type
    return typesMap
  }, {} as any)
}

const x = createActionTypes(['a', 'b'] as const)

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