reference type in Swift

ClassReferenceType.swift

class Book {
    var title: String
    
    init(title: String) {
        self.title = title
    }
}

var bookOne = Book(title: "A Game of Thrones (1996)")
var bookTwo = bookOne // bookTwo now refers to the same instance as bookOne

bookTwo.title = "A Storm of Swords (2000)"
print(bookOne.title) // Output: "A Storm of Swords (2000)"
print(bookTwo.title) // Output: "A Storm of Swords (2000)"
print("bookOne memory address: \(Unmanaged.passUnretained(bookOne).toOpaque())") // Output: Memory Address
print("bookTwo memory address: \(Unmanaged.passUnretained(bookTwo).toOpaque())") // Output: Memory Address