Readonly classes in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a readonly class in PHP.

PHP

<?php
[1] class User {
    public string $name;
}

Drag options to blanks, or click blank then click option'

Areadonly

Bfinal

Cabstract

Dstatic

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' instead of 'readonly' which prevents inheritance but not property changes.

Using 'static' which is unrelated to readonly properties.

In PHP 8.2+, the readonly keyword declares a class whose properties cannot be changed after initialization.

2fill in blank

medium

Complete the code to declare a readonly property in a normal class.

PHP

<?php
class Product {
    public [1] string $sku;
}

Drag options to blanks, or click blank then click option'

Areadonly

Bstatic

Cprivate

Dfinal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'static' which means the property belongs to the class, not instance.

Using 'final' which is for methods or classes, not properties.

The readonly keyword before a property means it can only be assigned once, typically in the constructor.

3fill in blank

hard

Fix the error in the readonly class constructor to properly assign the readonly property.

PHP

<?php
readonly class Order {
    public function __construct([1] string $id) {
    }
}

Drag options to blanks, or click blank then click option'

Areadonly

Bprivate

Cpublic

Dfinal

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'readonly' in constructor parameters which is invalid syntax.

Omitting visibility keyword causing property not to be assigned.

The constructor parameter should be declared with visibility like public to allow property promotion and assignment.

4fill in blank

hard

Fill the blank to create a readonly class with a readonly property using constructor property promotion.

PHP

<?php
[1] class Customer {
    public function __construct(public string $email) {}
}

Drag options to blanks, or click blank then click option'

Afinal

Breadonly

Cstatic

Dabstract

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' or 'static' instead of 'readonly' for the class.

Thinking you need readonly before the property type (it's invalid in readonly classes).

Declare the class readonly. Promoted properties are implicitly readonly in readonly classes.

5fill in blank

hard

Fill the blank to create a readonly class with two readonly properties and a method returning a property.

PHP

<?php
[1] class Invoice {
    public function __construct(public int $number, public float $amount) {}

    public function getAmount(): float {
        return $this->amount;
    }
}

Drag options to blanks, or click blank then click option'

Astatic

Bfinal

Cabstract

Dreadonly

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' instead of 'readonly' for the class.

Believing you need readonly keywords before each property type in the constructor.

Declaring the class readonly ensures all properties, including the two promoted ones, are readonly and immutable after creation.