Lets say I have an interface that accepts a generic:

interface ObjectKey<T extends {}>{
   key: keyof T
   doSomethingWithKey: (value: any) => void
}

Using it like this:

interface User {
   name: string,
   age: number,
   archived: boolean
}

const nameKey: ObjectKey<User> = {
   key: 'name', 
   doSomethingWithKey: (value) => console.log(value) // I want to infer value type here
}

As mentioned above i want to infer the 'value' argument type. Something like this:

interface ObjectKey<T extends {}>{
   key: keyof T
   doSomethingWithKey: (value: T[key]) => void
}

How can I achieve that?

I tried something like:

interface ObjectKey<T extends {}>{
   key: keyof T
   doSomethingWithKey: (value: { [Property in keyof T]: T[Property] }[keyof T]) => void
}

But it returns all available types of T. For example if we use User interface, 'value' argument would be 'string | number | boolean'

Playground link

CodePudding user response：

We can make ObjectKey a union type of all possible combinations by mapping over the object keys

type ObjectKey<T extends {}> = {
   [K in keyof T]: {
      key: K, 
      doSomethingWithKey: (value: T[K]) => void
   }
}[keyof T]

interface User {
   name: string,
   age: number,
   archived: boolean
}

const nameKey: ObjectKey<User> = {
   key: 'age', 
   doSomethingWithKey: (value) => console.log(value)
}

Playground