Could add Repeat type for array?

[WolfgangKurz]

Suggestion

🔍 Search Terms

Repeat , Array , Repeat Type

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

I'd like to shortnize repeated array types like this:

type Number32 = Repeat<number, 32>;

📃 Motivating Example

When i made my own Matrix class, there's some pretty uncomfortable code for matrix value type.

Code like this:

type Matrix4x4Value = [number, number, number, /* ... */ , number]; // 16 numbers!
type Matrix4x5Value = [number, number, number, /* ... */ , number]; // 20 numbers!!

Very tired and difficult to check about what times i wrote...

So i tried to use Repeat type for those, like this (with generated programatically code):

type Repeat1<T> = [T];
type Repeat2<T> = [T, T];
/* ... */
type Repeat16<T> = [T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T];
type Repeat17<T> = [T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T];
type Repeat18<T> = [T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T];
type Repeat19<T> = [T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T];
type Repeat20<T> = [T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T];
/* ... */
type Repeat100<T> = [T, T, T, T, T, T, T, T, /* ... */ , T, T, T, T]; // 100 T

export type Repeat<T, R extends Number> = R extends 1
	? Repeat1<T>
	: R extends 2
	? Repeat2<T>
	: R extends 3
	? Repeat3<T>
	: R extends 4
	? Repeat4<T>
	: R extends 5
	? Repeat5<T>
	...
	: R extends 15
	? Repeat15<T>
	: R extends 16
	? Repeat16<T>
	: R extends 17
	? Repeat17<T>
	: R extends 18
	? Repeat18<T>
	: R extends 19
	? Repeat19<T>
	: R extends 20
	? Repeat20<T>
	...
	: R extends 100
	? Repeat100<T>
	: T[]; // not defined, just use plain array

Looks very dirty code but works well.

And my Matrix code has changed to:

type Matrix4x4Value = Repeat<number, 16>; // Easy to use
type Matrix4x5Value = Repeat<number, 20>; // and Easy to know

Just for type-checking feature, as i think.

💻 Use Cases

Fixed-length single type array like Matrix value type as in Example section, to use in WebGL or something.

[MartinJohns]

Duplicate of #50838.

[WolfgangKurz]

Ah i missed it. Thanks!