Tuples & ReadonlyArray

Tuple Types

A tuple expresses a fixed‑length array with known element types.

let point: [number, number] = [10, 20];
// Access by index with proper types
let x = point[0]; // number

Optional Elements & Rest Elements

type Request = [method: string, url: string, body?: any];
let req1: Request = ["GET", "/users"];
let req2: Request = ["POST", "/users", { name: "Bob" }];

ReadonlyArray<T>

const nums: ReadonlyArray<number> = [1, 2, 3];
// nums.push(4); // ❌ error – read‑only

Spread with Tuples

function concat<T extends unknown[], U extends unknown[]>(...args: [...T, ...U]): [...T, ...U] {
  return args as any;
}