TypeScript`groupBy`类型 [英] TypeScript `groupBy` typings

问题描述

我想编写一个 groupBy 函数，到目前为止，类型系统对我的工作并不满意.

I want to write a groupBy function, so far the type system is not so happy with my work.

export function group<
    T extends object,
    K extends (keyof T & string),
    R = T[K] extends string ? string : never
>(
    data: T[],
    groupBy: keyof T
): { [group: R]: T[] }

我得到的第一个错误是 {[group:R]:T []} 中的 R 不是 string 或数字.

The first error that I got is that R in { [group: R]: T[] } is not string or number.

对于的数据集，签名实际上根本不起作用

The signature actually doesn't work at all for the data set of

group([{ name: 'Johnny Appleseed', age: 17 }], 'name') // R should be string
group([{ name: 'Johnny Appleseed', age: 17 }], 'age') // R should be never

但是，两个 R 都是从不，而 K 都是"name" |年龄"

However, both R is never while K is "name" | "age"

我必须使用 group< {name:string，age:number}，'name'> 来手动缩小类型参数，以使 R 为字符串.

I have to manually narrow down type parameter with group<{name: string, age: number}, 'name'> to make R be string.

推荐答案

索引签名必须为 string 或 number .没有联合类型，没有泛型类型，除了 string 或 number 之外，别无其他.

An index signature must be either string or number. No union types, no generic types nothing else will do except string or number.

如果您使用两个函数签名，一个仅接受 string 键，而另一个仅接受 number 键，我们仍然可以实现您想要的行为:

We can still achieve the behavior you want if you use two function signatures, one that accepts only string keys and the other that only accepts number keys:

export declare function group<T extends Record<K, string>, K extends string>(data: T[], groupBy: K): { [group: number]: T[] }
export declare function group<T extends Record<K, number>, K extends string>(data: T[], groupBy: K): { [group: string]: T[] }


let groupByString = group([{ name: 'Johnny Appleseed', age: 17 }], 'name') 
let groupByNumber = group([{ name: 'Johnny Appleseed', age: 17 }], 'age')

这篇关于TypeScript`groupBy`类型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！