Class Basics

// CLASS BASICS
// Classes are REFERENCE TYPES with inheritance support

// DEFINING A CLASS
class Person {
    var name: String
    var age: Int

    // Classes REQUIRE an initializer
    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }

    func introduce() {
        print("Hi, I'm \(name), \(age) years old")
    }
}

// CREATING INSTANCES
let person1 = Person(name: "Alice", age: 25)
person1.introduce()  // Hi, I'm Alice, 25 years old

// MODIFYING PROPERTIES
person1.name = "Alice Smith"
person1.age = 26

// CLASSES CAN HAVE let PROPERTIES
class Car {
    let brand: String      // Immutable after init
    var model: String
    var year: Int

    init(brand: String, model: String, year: Int) {
        self.brand = brand
        self.model = model
        self.year = year
    }

    func description() -> String {
        return "\(year) \(brand) \(model)"
    }
}

let myCar = Car(brand: "Tesla", model: "Model 3", year: 2023)
// myCar.brand = "BMW"  // ERROR: brand is let
myCar.model = "Model Y"  // OK: model is var
print(myCar.description())

// CLASS WITH DEFAULT VALUES
class User {
    var username: String
    var email: String
    var isActive: Bool = true
    var loginCount: Int = 0

    init(username: String, email: String) {
        self.username = username
        self.email = email
    }

    func login() {
        loginCount += 1
        print("\(username) logged in (\(loginCount) times)")
    }
}

let user = User(username: "john_doe", email: "[email protected]")
user.login()  // john_doe logged in (1 times)
user.login()  // john_doe logged in (2 times)

// CLASSES VS STRUCTS - KEY DIFFERENCE
// Classes are REFERENCE types
let person2 = person1  // Both point to SAME object!
person2.name = "Bob"
print(person1.name)  // Bob (changed!)

// This is different from structs which COPY!