How can one retrieve a specific type? The combination of T[keyof T] unifies all types into one

Question

How can one retrieve a specific type? The combination of T[keyof T] unifies all types into one

 const obj = {
      role  : 'admin',
      user : {
        id : 1,
        name : 'vasa',
      },
    }

const fun = <T>(obj: T):
      Record<`set${Capitalize<string & keyof T>}`, (a : T[keyof T]) => void>
      => {
      const action = {}
      for(const key in obj){
        action[key] = (value) => {console.log(value)}
      }
      return action
    }
    const action = fun(obj)

    // issue
    action.setRole({id: 2, name: 'bug'})

setRole is receiving the wrong type as T[keyof T] combines all types into one type when it's supposed to be:

setRole(string)

setUser(object)

typescript

Answer 1

Answer №1

Take a look at this scenario:

const obj = { role: 'admin', user: { id: 1, name: 'vasa', }, }

type Convert<Obj> = {
  [Prop in keyof Obj as `set${Capitalize<Prop & string>}`]: (value: Obj[Prop]) => void
}

const capitalize = <T extends string>(str: T) =>
  `${str[0].toUpperCase()}${str.substr(1)}` as Capitalize<T>;

const fun = <T extends Record<string, unknown>>(obj: T) =>
  (Object.keys(obj) as Array<keyof T & string>).reduce((acc, elem) => ({
    ...acc,
    [`set${capitalize(elem)}`]: (v: T[keyof T]) => { }
  }), {} as Convert<T>)

const action = fun(obj)



action.setRole('sdf') // ok
action.setUser({ id: 42, name: 'John' }) // ok
action.setUser('sdf') // error

key remmapping

Answer 2

Take a look at this scenario:

const obj = { role: 'admin', user: { id: 1, name: 'vasa', }, }

type Convert<Obj> = {
  [Prop in keyof Obj as `set${Capitalize<Prop & string>}`]: (value: Obj[Prop]) => void
}

const capitalize = <T extends string>(str: T) =>
  `${str[0].toUpperCase()}${str.substr(1)}` as Capitalize<T>;

const fun = <T extends Record<string, unknown>>(obj: T) =>
  (Object.keys(obj) as Array<keyof T & string>).reduce((acc, elem) => ({
    ...acc,
    [`set${capitalize(elem)}`]: (v: T[keyof T]) => { }
  }), {} as Convert<T>)

const action = fun(obj)



action.setRole('sdf') // ok
action.setUser({ id: 42, name: 'John' }) // ok
action.setUser('sdf') // error

key remmapping

How can one retrieve a specific type? The combination of T[keyof T] unifies all types into one

Answer №1

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