Use is.ReadonlyOf(is.UniformTupleOf(...)) instead.

To enhance performance, users are advised to cache the return value of this function and mitigate the creation cost.

import { is } from "@core/unknownutil";

const isMyType = is.ReadonlyUniformTupleOf(5);
const a: unknown = [0, 1, 2, 3, 4];
if (isMyType(a)) {
// a is narrowed to readonly [unknown, unknown, unknown, unknown, unknown]
const _: readonly [unknown, unknown, unknown, unknown, unknown] = a;
}

With predicate function:

import { is } from "@core/unknownutil";

const isMyType = is.ReadonlyUniformTupleOf(5, is.Number);
const a: unknown = [0, 1, 2, 3, 4];
if (isMyType(a)) {
// a is narrowed to readonly [number, number, number, number, number]
const _: readonly [number, number, number, number, number] = a;
}