type-fest/test-d/multidimensional-readonly-array.ts

import {expectType} from 'tsd';
import type {MultidimensionalReadonlyArray} from '../index';

function createArray<T extends number>(dimensions: T): MultidimensionalReadonlyArray<string, T> {
	const root: unknown[] = [];

	let array = root;
	for (let dimension = 1; dimension < dimensions; ++dimension) {
		console.log(`Initializing dimension #${dimension}`);

		array[0] = [];
		if (dimension < dimensions - 1) {
			array = array[0] as unknown[];
		} else {
			array[0] = '42';
		}
	}

	return root as MultidimensionalReadonlyArray<unknown, T> as MultidimensionalReadonlyArray<string, T>;
}

const a: MultidimensionalReadonlyArray<number, 3> = [];
const b: MultidimensionalReadonlyArray<boolean, number> = [];
const c = createArray(2);

const answer = c[0][0]; // '42'

type RecursiveArray<T> = ReadonlyArray<RecursiveArray<T>>;

expectType<string>(answer);

expectType<ReadonlyArray<ReadonlyArray<readonly number[]>>>(a);
expectType<RecursiveArray<boolean>>(b);
expectType<ReadonlyArray<readonly string[]>>(c);