A Fixed-size Array type for TypeScript.

sized_array.ts

export type SizedArray<N extends number, T> = SizedArrayInner<N, T, []>;

type SizedArrayInner<
    N extends number,
    T,
    Acc extends unknown[],
> = N extends PositiveInteger<N>
    ? number extends N
        ? T[]
        : N extends Acc["length"]
        ? Acc
        : SizedArrayInner<N, T, [T, ...Acc]>
    : never;

type PositiveInteger<N extends number> = N extends 0
    ? never
    : `${N}` extends `${number}.${number}`
    ? never
    : `${N}` extends `-${number}`
    ? never
    : N;