Readonly properties in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

PHP

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

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

Aconst

Bprivate

Cstatic

Dreadonly

Attempts:

3 left

💡 Hint

Common Mistakes

Using const instead of readonly for properties.

Using static which is unrelated to immutability.

The readonly keyword declares a property that can only be assigned once, typically in the constructor.

2fill in blank

medium

Complete the constructor to assign a value to the readonly property.

PHP

<?php
class User {
    public readonly string $name;

    public function __construct([1]) {
        $this->name = $name;
    }
}

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

Astring $name

Bint $name

Cbool $name

Darray $name

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different type like int or bool which causes type errors.

Not declaring the parameter type at all.

The constructor parameter must match the property type string to assign it correctly.

3fill in blank

hard

Fix the error by completing the code to prevent modifying a readonly property after construction.

PHP

<?php
class User {
    public readonly string $name;

    public function __construct(string $name) {
        $this->name = $name;
    }

    public function changeName([1]) {
        $this->name = $newName;
    }
}

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

Aarray $newName

Bint $newName

Cstring $newName

Dbool $newName

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to assign a new value to a readonly property after construction.

Using a wrong parameter type.

The method tries to assign a new value to a readonly property, which is not allowed. The parameter type should be string, but the assignment itself will cause an error.

4fill in blank

hard

Fill both blanks to create a readonly property and assign it in the constructor.

PHP

<?php
class Product {
    public [1] int $id;

    public function __construct([2]) {
        $this->id = $id;
    }
}

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

Areadonly

Bstring $id

Cint $id

Dprivate

Attempts:

3 left

💡 Hint

Common Mistakes

Using string type for the constructor parameter when property is int.

Forgetting the readonly keyword.

The property is declared as readonly and of type int. The constructor parameter must match the type int $id to assign it properly.

5fill in blank

hard

Fill all three blanks to declare a readonly property, assign it in the constructor, and prevent modification.

PHP

<?php
class Order {
    public [1] float $amount;

    public function __construct([2]) {
        $this->amount = $amount;
    }

    public function updateAmount([3]) {
        $this->amount = $newAmount;
    }
}

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

Areadonly

Bfloat $amount

Cfloat $newAmount

Dprivate

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to modify a readonly property after construction.

Using mismatched types for parameters.

The property is declared readonly and of type float. The constructor parameter matches the property type. The update method tries to assign a new value, but this will cause an error because the property is readonly.