Use is.ReadonlyOf(is.TupleOf(...)) 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.ReadonlyTupleOf([is.Number, is.String, is.Boolean]);
const a: unknown = [0, "a", true];
if (isMyType(a)) {
// a is narrowed to readonly [number, string, boolean]
const _: readonly [number, string, boolean] = a;
}

With predElse:

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

const isMyType = is.ReadonlyTupleOf(
[is.Number, is.String, is.Boolean],
is.ArrayOf(is.Number),
);
const a: unknown = [0, "a", true, 0, 1, 2];
if (isMyType(a)) {
// a is narrowed to readonly [number, string, boolean, ...number[]]
const _: readonly [number, string, boolean, ...number[]] = a;
}

Depending on the version of TypeScript and how values are provided, it may be necessary to add as const to the array used as predTup. If a type error occurs, try adding as const as follows:

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

const predTup = [is.Number, is.String, is.Boolean] as const;
const isMyType = is.ReadonlyTupleOf(predTup);
const a: unknown = [0, "a", true];
if (isMyType(a)) {
// a is narrowed to readonly [number, string, boolean]
const _: readonly [number, string, boolean] = a;
}