Typescript 接口特定的属性设置函数

Question

I have an interface "Example" and I want to create a function that will get key (name of property from Example) and new value for that key. But i don't understand how to write types for that, now I code smth but this is not work.

interface Example {
  num: number;
  str: string;
}

const obj: Example = {
  num: 5,
  str: '123'
}

const setExampleProp = ({key, value}: {
  key: keyof Example;
  value: Example[keyof Example];
}) => {
  obj[key] = value
}

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

Answer 1

Change it to a generic function

function setExampleProp<T extends keyof Example>({key, value}: {
  key: T;
  value: Example[T];
}) {
  obj[key] = value
}

Answer 2

The answer above is valid.

Another approach would be to add a index signature to your interface:

interface Example {
  num: number;
  str: string;

  [name: string]: Example[keyof Example];
}