type-challenges-solutions/en/easy-tuple-to-object about type-challenges-solutions HOT 5 OPEN

To pass the last spec:

// @ts-expect-error
type error = TupleToObject<[[1, 2], {}]>

We need to ensure the input type is only an array of strings:

type TupleToObject<T extends readonly string[]> = {
  [P in T[number]]: P
}

from type-challenges-solutions.

@Brysonmk1984 without it, you will get an error:

The type 'readonly ["tesla", "model 3", "model X", "model Y"]' is 'readonly' and cannot be assigned to the mutable type 'PropertyKey[]'.

Since input to the type is [] as const it is treated as readonly, so we need to specify it as readonly in our type as well.

from type-challenges-solutions.

@hpr Why not replace string with string | number | symbel?
like this

type TupleToObject<T extends readonly (keyof any)[]> = {
  [k in T[number]]: k
}

from type-challenges-solutions.

type TupleToObject<T extends readonly (string | number)[]> = { [K in T[number]]: K }

from type-challenges-solutions.

Can anyone explain why readonly is necessary here?

from type-challenges-solutions.