Interfaces आणि Type Aliases

// Interface define करा
interface Student {
  id: number;
  name: string;
  age: number;
  email?: string;       // optional
  readonly rollNo: string; // read-only
}

// Use करा
const student: Student = {
  id: 1,
  name: "Avadhoot",
  age: 22,
  rollNo: "CS101",
};

student.rollNo = "CS102"; // ❌ ERROR: readonly

// Interface extend करा
interface GradStudent extends Student {
  thesis: string;
  supervisor: string;
}

// Type alias
type Point = {
  x: number;
  y: number;
};

// Union type alias
type Status = "active" | "inactive" | "pending";

// Intersection type
type AdminUser = Student & {
  adminLevel: number;
  permissions: string[];
};

let userStatus: Status = "active";
userStatus = "deleted"; // ❌ ERROR — not in union