Deinitializers for cleanup in Swift - Mini Project: Build & Apply

Deinitializers for cleanup

📖 Scenario: Imagine you are managing a simple library system where books are borrowed and returned. When a book is no longer needed, it should clean up by announcing it is removed from the system.

🎯 Goal: You will create a Book class with a deinitializer that prints a message when a book object is removed from memory.

📋 What You'll Learn

Create a Book class with a title property

Add an initializer to set the title

Add a deinitializer that prints a message including the title

Create and remove book instances to see the deinitializer in action

💡 Why This Matters

🌍 Real World

Deinitializers are used in apps to release resources like files, network connections, or memory when objects are no longer needed.

💼 Career

Understanding deinitializers is important for Swift developers to write efficient, memory-safe apps and avoid resource leaks.

1

Create the Book class with a title property

Create a class called Book with a property title of type String. Add an initializer that takes a title parameter and sets the property.

Swift

# Create the Book class with a title property and initializer

Need a hint?

Use class Book to define the class. Use let title: String for the property. Write an init method to set title.

2

Add a deinitializer to announce when a book is removed

Add a deinitializer deinit inside the Book class that prints "Removing book titled: \(title)".

Swift

class Book {
    let title: String
    
    init(title: String) {
        self.title = title
    }
    // Add deinitializer here
}

Need a hint?

Use deinit { } to define the deinitializer. Inside it, use print with the message including title.

3

Create a book instance and then remove it

Create a variable myBook and assign it a new Book instance with the title "Swift Programming". Then set myBook to nil to remove the instance.

Swift

class Book {
    let title: String
    
    init(title: String) {
        self.title = title
    }
    
    deinit {
        print("Removing book titled: \(title)")
    }
}

// Create and remove a book instance

Need a hint?

Create myBook as an optional Book and assign it a new instance. Then set myBook = nil to trigger the deinitializer.

4

Run the program to see the deinitializer output

Run the program and observe the output. It should print Removing book titled: Swift Programming when myBook is set to nil.

Swift

class Book {
    let title: String
    
    init(title: String) {
        self.title = title
    }
    
    deinit {
        print("Removing book titled: \(title)")
    }
}

var myBook: Book? = Book(title: "Swift Programming")
myBook = nil

// Run the program to see the output

Need a hint?

When you run the program, the message from the deinitializer should appear in the output.