TypeScript array with arbitrary minimum length N, which can be large

Question

I want to create a type where an array has a minimum length of N. I have looked at this TypeScript array with minimum length , but when N is large, I do not want to write out the type from 0 to N, e.g. :

type ArrayTwoOrMore<T> = {
    0: T
    1: T
    ...
    N: T
}

I was wondering whether there was a neater way of doing this?

If you are using a recent version of TS, the other answer there is better namely type ArrayTwoOrMore<T> = [T, T, ...T[]], but you still need to spell out all members, no way to say greater than N — Titian Cernicova-Dragomir
– Titian Cernicova-Dragomir, Commented Jun 23, 2020 at 13:40
For info: typescript-how-to-declare-array-of-fixed-size-for-type-checking-at-compile-time — Orelsanpls
– Orelsanpls, Commented Jun 23, 2020 at 15:01
In Typescript you can create types like this type Pair<T, U> = [T, U] and type Tripple<T> = [T, T, T] I think @TitianCernicova-Dragomir answer is the best you can get with typescript in one line of code — user11534547
– user11534547, Commented Jun 24, 2020 at 9:53
not sure why I did not think of this yesterday, in 4.0 this will be easier. 10x @IAMTHEBEST for bringing the question back in my mind :) — Titian Cernicova-Dragomir
– Titian Cernicova-Dragomir, Commented Jun 24, 2020 at 10:34

Titian Cernicova-Dragomir · Accepted Answer · 2020-06-24 10:33:46Z

3

You can't do arbitrary tuple size, but in 4.0 you will be able to create a type like Typle5 or Tuple10 and spread that multiple times to get to the desired type faster:

type Tuple5<T> = [T, T, T, T, T]
type Tuple10<T> = [...Tuple5<T>, ...Tuple5<T>]
type Tuple50<T> = [...Tuple10<T>, ...Tuple10<T>, ...Tuple10<T>, ...Tuple10<T>, ...Tuple10<T>]
type Tuple100<T> = [...Tuple50<T>, ...Tuple50<T>]

let a: Tuple100<number> = [] // Source has 0 element(s) but target requires 100

Playground Link

I would question the sanity of creating a tuple of size 100 though.

NOTE: 4.0 is still in beta should be released in August 2020

answered Jun 24, 2020 at 10:33

Titian Cernicova-Dragomir

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