How to declare array of N elements of custom type in Typescript?

Question

I have created my own type called tuple, and I want to make an array, of length 10, with elements of type tuple. How do I do that (possibly) with that specific Array syntax, or any other?

type tuple =  [number, number]

var numbers: Array<tuple> = []

There's nothing wrong with your posted code. Do you mean that you want a type that is a tuple of 10 of the [number, number] tuple type? Or do you want to create a tuple[] array at runtime with 10 items in it? Which part there are you having trouble with? Please edit your question and add some information about your desired result. — Alex Wayne
– Alex Wayne, Commented Sep 22, 2022 at 17:39
Sorry for bad explaining. Desired outcome is to have an array of length 10, where every item is of type tuple, so I could just ,for example, in very next line say numbers[3] = [3,15]; without actually having to push items first to get 3rd spot — w1atrak
– w1atrak, Commented Sep 22, 2022 at 17:56

iced · Accepted Answer · 2022-09-22 21:40:57Z

1

Just to add a separate answer if you're okay with having default values for your tuple, something like this could work:

type tuple = [number, number]
type TupleArray<tuple, TupleLen extends number> = [tuple, ...tuple[]] & { length: TupleLen }

let numbers: TupleArray<tuple, 10> = Array(10).fill([0, 0]) as TupleArray<tuple, 10>;

With this approach, you're specifically typing TupleArray to have a specific length, so there is the added caveat of an empty array or any array above or below a length of 10 would throw an error. This is also why you need to fill your array with 10 tuples.

edited Sep 22, 2022 at 21:40

answered Sep 22, 2022 at 21:35

iced

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k.tten · Accepted Answer · 2022-09-22 17:08:55Z

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Make it a tuple of tuples? Or specifically, a tuple of the type tuple you already have.

type tuple =  [number, number];

const numbers: [tuple, tuple, tuple, tuple, ...] = [...];

answered Sep 22, 2022 at 17:08

k.tten

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1 Comment

w1atrak Over a year ago

Actually haven't thought about it. But this could be hard if I want higher array lengths. Of course I could push empty elements, but was hoping for neat solution

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