Typescript capture type at key in array as in object-like structure

Question

Let say i have a structure like this:

type Dict<T = any> = {[key: string]: T}

type AsObject<T extends Dict> = {
  [K in keyof T]: (x: any) => T[K]
}

What i do need is the same structure as an array, but how to capture the type for that specific key in the function?

type AsArray<T extends Dict> = {
  key: keyof T
  fn: (x: any) => T[??] // how to get typeof key from here ?
}[]

Record<T> is an existing type that covers what your Dict type does — spender
– spender, Commented Apr 7, 2019 at 11:15
Could you explain better what do you mean by key in function? As a in a key in the object return of that function? as functions unlike objects do not have keys — Ali Habibzadeh
– Ali Habibzadeh, Commented Apr 7, 2019 at 13:43
@AliHabibzadeh i ment by key the specific key in the object holding a function (in AsObject) — zedryas
– zedryas, Commented Apr 8, 2019 at 18:58

Titian Cernicova-Dragomir · Accepted Answer · 2019-04-07 15:38:13Z

3

If you want to ensure the array items have the corect combination of type and fn, you can, using a mapped type, create a union of al valid possibilities for the array item and then use this to define the array:

type Dict<T = any> = Record<string, T>

type AllPosibilities<T extends Dict> = {
    [K in keyof T]: {
        type: K,
        fn: (x: any) => T[K]
    }
}[keyof T]

type AsArray<T extends Dict> = AllPosibilities<T>[]

let arr : AsArray <{
    "a": string,
    "b": number
}> = [
    { type: "a", fn: (x) => "" }, //ok
    { type: "b", fn: (x) => "" },// err
    { type: "b", fn: (x) => 1 }  //ok
]

answered Apr 7, 2019 at 15:38

Titian Cernicova-Dragomir

253k37 gold badges464 silver badges394 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Typescript capture type at key in array as in object-like structure

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related