打字稿 - 使用键变量更改字典的值 [英] Typescript - change value of a dictionary with a key variable

问题描述

我有一个对象:

const sampleExpenseData = {
  Time: "11-12-19",
  Meals: 5130,
  Pantry: 10,
  Living: 10,
  Others: 0,
  Total: 74
}

我想定义一个函数来更新特定键的值，到目前为止我所拥有的是:

I would like to define a function such that it will update the value of a specific key, what I have so far is:

const updateValueInDict = (
  obj: typeof sampleExpenseData,
  key: keyof typeof sampleExpenseData,
  upDatedValue: string | number
): void => {
  obj[key] = upDatedValue  // this line throws error
}

错误说:

输入'字符串|number' 不能分配给类型 'never'.

Type 'string | number' is not assignable to type 'never'.

类型 'string' 不可分配给类型 'never'.ts(2322)

Type 'string' is not assignable to type 'never'.ts(2322)

TIA!!!

推荐答案

这里的问题是，如果您要为任意键分配一个值，那么该值必须具有可分配给您可能使用的每个键的类型将其分配给.这意味着值的类型必须是 string &number 以便可以分配给 string 和 number 属性类型.交集 string &number 是 never.

The problem here is that if you're assigning a value to an arbitrary key, then that value must have a type which is assignable to every key you might be assigning it to. That means the value's type has to be string & number in order to be assignable to both string and number property types. The intersection string & number is never.

解决方案是使用泛型类型，这样 upDatedValue 被约束为根据 key 的类型具有正确的类型:

The solution is to use a generic type, so that upDatedValue is constrained to have the right type depending on the type of key:

const updateValueInDict = <K extends keyof typeof sampleExpenseData>(
  obj: typeof sampleExpenseData,
  key: K,
  upDatedValue: (typeof sampleExpenseData)[K]
): void => {
  obj[key] = upDatedValue
}

这也意味着在调用函数时可以更严格地对参数进行类型检查.

This also means that the arguments can be type-checked more strictly when the function is called.

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