Typescript generic with Tuple type

Question

What I want is simple: I want to define a tuple type whose second argument is T[] if the first argument is determined to be T.

I can do this.

type TandTArray<T> = [T, T[]]

But, i had to specify every T

But i want it to be determined by the first argument automatically.
I tried this But dosen't work

type TandTArray = <T>[T, T[]]

Aleksey L. · Accepted Answer · 2022-03-06 12:48:40Z

3

You'll need a function for generic type to be inferred:

const tandTArray = <T>(x: [T, T[]]) => x;

const foo = tandTArray([1, [1]])

answered Mar 6, 2022 at 12:48

Aleksey L.

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2 Comments

Ummm... I would be sad if there is no way to define it without function But in second thought, I notice that this might impossible.

Using generic type without generic parameter is only possible with default type parameter, but this won't help here.