TypeScript: tuple type to object type

Question

Consider a tuple like this:

type MyTuple = [A, B];

where A and B both have an attribute named key. For instance,

interface A = {
  key: 'sandwiches'
}

interface B = {
  key: 'pasta'
}

I desire the following interface:

interface Result {
  sandwiches: A;
  pasta: B;
}

Is there a way to do this dynamically?

I'm thinking that, if this is achievable, it might look something like:

type MapTuple<T> = {
  [K in keyof T]: T[K]["key"]
}

but this doesn't work.

This question is the inverse of Typescript: object type to array type (tuple)

I think typescript typing is only available at compile-time -- what do you mean with 'Is there a way to do this dynamically?' Do you just want to have the Result interface inferred at compile-time or are you looking for a run-time solution? — Simon Groenewolt
– Simon Groenewolt, Commented Feb 8, 2019 at 20:11

Titian Cernicova-Dragomir · Accepted Answer · 2019-02-08 20:14:05Z

10

This will produce the desired effect. You need to map over all the key properties of the tuple and extract the tuple member for each key :

type MyTuple = [A, B];

interface A {
  key: 'sandwiches'
}

interface B {
  key: 'pasta'
}


type MapTuple<T extends Array<{ key: string }>> = {
  [K in T[number]['key']]: Extract<T[number], { key : K}>
}

type R = MapTuple<MyTuple>

answered Feb 8, 2019 at 20:14

Titian Cernicova-Dragomir

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2 Comments

jamesplease Over a year ago

Thank you, this is working! I'll accept this as the answer in a few minutes, once I'm able to.

Przemyslaw Jan Beigert Over a year ago

Very nice! Btw [K in T[number]['key']]: K this will woks the same as Extract<T[number], { key : K}>

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