无法将属性分配给接口中的字符串索引 [英] Property is not assignable to string index in interface

问题描述

我有以下界面:

export interface Meta {
  counter: number;
  limit: number;
  offset: number;
  total: number;
}

export interface Api<T> {
  [key: string]: T[];
  meta: Meta; // error
}

当前，我收到以下错误:

Currently, I'm receiving the following error:

类型元"的属性元"不可分配给字符串索引 输入"T []".

Property 'meta' of type 'Meta' is not assignable to string index type 'T[]'.

经过一番搜索，我在 TS文档中找到了该语句> :

After searching a bit, I found this statement in TS docs:

虽然字符串索引签名是描述 字典"模式，它们还强制所有属性匹配 他们的返回类型.这是因为字符串索引声明 obj.property也可以作为obj ["property"]使用.

While string index signatures are a powerful way to describe the "dictionary" pattern, they also enforce that all properties match their return type. This is because a string index declares that obj.property is also available as obj["property"].

这是否意味着当我具有字符串索引签名时，如果不匹配此类型，就无法拥有任何其他变量?

Does it means that when I have a string index signature, I can't have any other variable without match this type?

实际上，我可以摆脱这样的错误，像这样声明接口:

Actually I can get rid of this error declaring the interface like this:

export interface Api<T> {
  [key: string]: any; // used any here
  meta: Meta;
}

这样做，我完全失去了类型推断的能力.没有这种丑陋的方法，有什么方法可以做到这一点?

Doing this, I lose the completely ability of type inference. Is there any way to do this without this ugly way?

推荐答案

您可以使用两个界面的交点:

interface Api<T> {
    [key: string]: T[];  
}

type ApiType<T> = Api<T> & {
    meta: Meta;
}

declare let x: ApiType<string>;

let a = x.meta // type of `a` is `Meta`
let b = x["meta"]; // type of `b` is `Meta`

let p = x["someotherindex"] // type of `p` is `string[]`
let q = x.someotherindex // type of `q` is `string[]`

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