How can I map an array of types to another array of types in Typescript?

Question

Let's say I have this:

type CoolTuple = [string, number, boolean]

And, I want to map that type using some generic:

type CoolGeneric<T extends any[]> = ...

Such that:

CoolGeneric<CoolType> is [Wrapper<string>, Wrapper<number>, Wrapper<boolean>]

What would I do?

Alex Wayne · Accepted Answer · 2021-10-28 23:04:37Z

2

You want a mapped type:

type CoolGeneric<T extends any[]> = { [K in keyof T]: Wrapper<T[K]> }

Basically, for each key (indices of a tuple are keys), declare the type to be something that uses the property type T[K].

Playground

answered Oct 28, 2021 at 23:04

Alex Wayne

188k52 gold badges328 silver badges363 bronze badges

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

5 Comments

lmonninger Over a year ago

Oh, I didn't realize this worked for arrays.

Alex Wayne Over a year ago

A tuple is basically just an object with sequential integer keys.

lmonninger Over a year ago

Yeah, makes sense.

jcalz Over a year ago

"a tuple is basically just an object with sequential integer keys"... well, it also has non-integer keys like "length" and "push" and you don't want to map those (so that you get a length of type Wrapper<number> and a push of type Wrapper<(...items: (string | number | boolean)[]) => number>). TypeScript 3.1 added support to have mapped types turn arrays/tuples into arrays/tuples and that change stopped treating them like "just an object".

lmonninger Over a year ago

@AlexWayne I just started running into a situation where this creates unions of the wrapper types as opposed to interpreting them as a progressive tuple? Any idea why this could be?

Collectives™ on Stack Overflow

How can I map an array of types to another array of types in Typescript?

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related