Readonly properties in PHP - Mini Project: Build & Apply

Readonly properties

📖 Scenario: Imagine you are creating 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 title and author should not change.

🎯 Goal: You will create a PHP class with readonly properties for title and author. Then, you will create an object of this class and display its properties.

📋 What You'll Learn

Create a class called Book with readonly properties title and author

Add a constructor to set the values of title and author

Create an object of the Book class with title '1984' and author 'George Orwell'

Print the title and author of the book

💡 Why This Matters

🌍 Real World

Readonly properties are useful when you want to store data that should not change after creation, like IDs, names, or fixed settings.

💼 Career

Understanding readonly properties helps you write safer and more reliable code, which is important in professional PHP development.

1

Create the Book class with readonly properties

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

PHP

<?php

// Create class Book with readonly properties title and author

Need a hint?

Use the readonly keyword before the property type and name.

2

Add a constructor to set the readonly properties

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

PHP

<?php

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

    // Add constructor here

}

Need a hint?

The constructor sets the readonly properties only once when the object is created.

3

Create a Book object with title and author

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

PHP

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

// Create a Book object with title '1984' and author 'George Orwell'

Need a hint?

Use the new keyword to create the object and pass the exact strings.

4

Print the book's title and author

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

PHP

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

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

// Print the book's title and author

Need a hint?

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