为什么这段代码说类型'string'不能分配给类型'never'

编程问答 2022-06-22

问题描述

为什么下面的代码说Type 'string' is not assignable to type 'never'？

但是，已编译的javascript效果很好

export enum MyStringsTest {
    DEPART_IN_X_MINUTE='DEPART_IN_X_MINUTE',A_DRIVER_IS_ASKING_FOR='A_DRIVER_IS_ASKING_FOR',}
export interface Payloads {
    [MyStringsTest.DEPART_IN_X_MINUTE]: number,[MyStringsTest.A_DRIVER_IS_ASKING_FOR]: string,}

type Cache = {
  [K in keyof Payloads]?: (payload: Payloads[K]) => string
}

const cache: Cache = {}
function addToCache<K extends keyof Cache>(code: K,cb: (Cache[K])): void{
    cache[code] = cb
}
addToCache(MyStringsTest.DEPART_IN_X_MINUTE,(data) => `Depart in ${data} minutes!`);
addToCache(MyStringsTest.A_DRIVER_IS_ASKING_FOR,(data) => `a driver is asking for ${data}`);

function getParsed<T extends keyof Cache>(stringCode: T,payload: Payloads[T]) {
    const builder = cache[stringCode]
    const ans = builder(payload as any) // <- error here
    return ans;
}

getParsed(MyStringsTest.A_DRIVER_IS_ASKING_FOR,'a sandwitch')
getParsed(MyStringsTest.DEPART_IN_X_MINUTE,456)
// This prints "a driver is asking for a sandwitch"
// This prints "Depart in 456 minutes!"

跟踪Why is this code saying Type 'number' is not assignable to type 'never'

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解决方法

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