Null safe operator in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using the null safe operator?

Consider the following PHP code snippet. What will it output?

PHP

<?php
class Profile {
    public ?string $email = null;
}
class User {
    public ?Profile $profile = null;
}

$user = new User();
echo $user->profile?->email ?? 'No email';
?>

A No email

B Error: Trying to access property on null

C null

D Empty string

💡 Hint

The null safe operator returns null if the left side is null, so the null coalescing operator will provide the fallback.

The ?-> operator safely accesses email only if profile is not null. Since profile is null, $user->profile?->email returns null, so the ?? operator outputs 'No email'.

❓ Predict Output

intermediate

What does this PHP code print when using the null safe operator with nested objects?

Given the code below, what will be printed?

PHP

<?php
class Engine {
    public ?string $type = 'V8';
}
class Car {
    public ?Engine $engine = null;
}

$car = new Car();
echo $car->engine?->type ?? 'No engine';
?>

A No engine

B V8

C null

D Error: Undefined property

💡 Hint

Check if engine is set before accessing type.

The engine property is null, so $car->engine?->type returns null. The null coalescing operator then outputs 'No engine'.

❓ Predict Output

advanced

What is the output of this PHP code using null safe operator with method chaining?

Analyze the code below and select the correct output.

PHP

<?php
class Address {
    public ?string $city = 'Paris';
}
class User {
    public ?Address $address = null;
    public function getAddress(): ?Address {
        return $this->address;
    }
}

$user = new User();
echo $user->getAddress()?->city ?? 'Unknown city';
?>

A null

B Paris

C Unknown city

D Fatal error: Call to a member function on null

💡 Hint

Consider what getAddress() returns and how the null safe operator works with method calls.

The method getAddress() returns null because address is null. The null safe operator prevents an error and returns null, so the null coalescing operator outputs 'Unknown city'.

❓ Predict Output

advanced

What is the output of this PHP code using null safe operator on null?

What will this code output?

PHP

<?php
class Book {
    public ?string $title = 'PHP Guide';
}

$book = null;
echo $book?->title;
?>

A Fatal error: Call to undefined method string::title()

B No output, prints nothing

C Parse error: syntax error, unexpected '?->'

D Fatal error: Call to a member function title() on null

💡 Hint

The null safe operator short-circuits when the left side is null and does not evaluate the right side.

Since $book is null, the null safe operator ?-> returns null immediately without attempting to call the non-existent title() method (note: title is a property, not a method). echo null; produces no output.

🧠 Conceptual

expert

How many items are in the resulting array after this PHP code runs?

Consider this PHP code using null safe operator inside a loop. How many items will the $results array contain?

PHP

<?php
class Item {
    public ?string $name;
    public function __construct(?string $name) {
        $this->name = $name;
    }
}

$items = [new Item('A'), null, new Item(null), new Item('D')];
$results = [];
foreach ($items as $item) {
    $results[] = $item?->name ?? 'Unknown';
}
print_r($results);
?>

A 1

B 3

C 2

D 4

💡 Hint

Count how many times the loop runs and what values are added to $results.

The loop runs 4 times. For each $item, the null safe operator safely accesses name. If $item is null or name is null, 'Unknown' is added. So $results has 4 items.