Property Modifiers in TypeScript

interface Config {
  url: string;
  timeout?: number;
  retries?: number;
  headers?: Record<string, string>;
}

// Usage
const config: Config = { url: "https://api.example.com" };

interface User {
  readonly id: string;
  readonly createdAt: Date;
  name: string;
}

const user: User = { id: "1", createdAt: new Date(), name: "Alice" };
// user.id = "2"; // ❌ Error

type Brand<T, B> = T & { __brand: B };

type UserId = Brand<string, "UserId">;
type OrderId = Brand<string, "OrderId">;

function getUser(id: UserId): User { /* ... */ }
function getOrder(id: OrderId): Order { /* ... */ }

const userId = "abc" as UserId;
const orderId = "xyz" as OrderId;

getUser(userId);  // OK
getUser(orderId); // ❌ Error even though both are strings!