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niedzielski/reverse.d.ts

Last active December 27, 2023 16:22
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Reverse a type's keys and values in TypeScript.
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reverse.d.ts
type Reverse<T> = {[V in T[keyof T] & keyof T]: keyof T}
@maheshjag
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maheshjag commented Dec 27, 2023

Would this not be

type Reverse<T> = {[V in T[keyof T]]: keyof T}

instead?

@niedzielski
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niedzielski commented Dec 27, 2023

What I wrote looks incorrect. Yours looks right but I think you'll want to constraint the keys to valid key types only (eg, keyof any, string | number | symbol, or PropertyKey):

type Reverse<T> = {[V in T[keyof T] & PropertyKey]: keyof T}

Ex

I think this is what I used the most recent time I needed to flip keys and values:

export type Inverse<T extends Invertible> = {
  [Key in keyof T as T[Key]]: Key
}

export type Invertible = Record<PropertyKey, PropertyKey>

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