webstorm typescript tuple arithmetic

example.ts

type buildTuple<
	n extends number,
	acc extends any[] = [],
> = acc["length"] extends n ? acc : buildTuple<n, [...acc, 0]>;

type add<a extends number, b extends number> = [
	...buildTuple<a>,
	...buildTuple<b>,
]["length"] &
	number;

type subtract<a extends number, b extends number> = buildTuple<a> extends [
	...buildTuple<b>,
	...infer rest,
]
	? rest["length"]
	: never;

type addResult = add<2, 5>;
type subResult = subtract<5, 2>;