Readonly classes in PHP - Mini Project: Build & Apply

Readonly Classes in PHP

📖 Scenario: You are building a simple system to store information about books in a library. Each book has a title and an author. Once a book is created, its details should not change.

🎯 Goal: Create a readonly class called Book with two properties: title and author. Initialize these properties in the constructor and then display the book details.

📋 What You'll Learn

Create a readonly class named Book

Add two public properties: title and author

Initialize these properties using a constructor

Create an instance of Book with specific values

Print the book's title and author

💡 Why This Matters

🌍 Real World

Readonly classes are useful when you want to create objects that should not change after creation, such as configuration settings, fixed data records, or value objects.

💼 Career

Understanding readonly classes helps you write safer and more predictable code, which is important in professional PHP development to avoid bugs and maintain data integrity.

1

Create the readonly class with properties

Create a readonly class called Book with two public properties: title and author.

PHP

<?php

// Define the readonly class Book with public properties title and author
// Your code here

Need a hint?

Use the readonly keyword before class. The properties are implicitly readonly.

2

Add the constructor to initialize properties

Add a constructor method __construct to the Book class that takes two parameters: string $title and string $author. Inside the constructor, assign these parameters to the readonly properties $title and $author.

PHP

<?php

readonly class Book {
    public string $title;
    public string $author;

    // Add the constructor here
    // Your code here
}

Need a hint?

Use public function __construct(string $title, string $author) and assign the parameters to the properties.

3

Create an instance of the readonly class

Create a variable called $book and assign it a new instance of the Book class with the title '1984' and author 'George Orwell'.

PHP

title = $title;
        $this->author = $author;
    }
}

// Create a new Book instance with title '1984' and author 'George Orwell'
// Your code here

Need a hint?

Use new Book('1984', 'George Orwell') and assign it to $book.

4

Print the book details

Print the book's title and author using echo in the format: Title: 1984, Author: George Orwell.

PHP

title = $title;
        $this->author = $author;
    }
}

$book = new Book('1984', 'George Orwell');

// Print the book details below
// Your code here

Need a hint?

Use echo and access the properties with $book->title and $book->author.