Structs and Classes

import Foundation

// Struct: value type
struct PointStruct {
    var x: Double
    var y: Double
    mutating func moveBy(dx: Double, dy: Double) {
        x += dx; y += dy
    }
}

// Class: reference type, supports inheritance and deinit
class Animal {
    let name: String
    init(name: String) { self.name = name }
    func speak() -> String { "\(name) makes a sound" }
    deinit { print("\(name) deinit") }
}

class Dog: Animal {
    override func speak() -> String { "\(name) says woof" }
}

// Value semantics: copy on assignment
var p1 = PointStruct(x: 1, y: 2)
var p2 = p1
p2.moveBy(dx: 10, dy: 10)
print(p1, p2)   // p1 unchanged

// Reference semantics: shared instance
let a = Dog(name: "Rex")
let b = a
print(a.speak(), b.speak())

// Equatable conformance
struct Money: Equatable {
    let amount: Double
    let currency: String
    static func == (l: Money, r: Money) -> Bool {
        l.amount == r.amount && l.currency == r.currency
    }
}
print(Money(amount: 5, currency: "USD") == Money(amount: 5, currency: "USD"))