Null safe operator in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the null safe operator in PHP?

The null safe operator is ?->. It helps safely access properties or methods on an object that might be null, avoiding errors.

beginner

How does the null safe operator prevent errors?

If the object before ?-> is null, PHP returns null instead of throwing an error. This stops the program from crashing.

beginner

Example: What does $user?->getName() do if $user is null?

It returns null instead of calling getName() and causing an error.

intermediate

Can the null safe operator be chained in PHP?

Yes! You can chain it like $user?->profile?->getAddress(). If any part is null, the whole expression returns null safely.

beginner

When was the null safe operator introduced in PHP?

It was introduced in PHP 8.0 to make code safer and cleaner when dealing with nullable objects.

What does the null safe operator ?-> do in PHP?

A Accesses a property or method only if the object is not null

B Always throws an error if the object is null

C Assigns null to a variable

D Checks if a variable is set

The null safe operator accesses properties or methods only if the object is not null, preventing errors.

What will $user?->getEmail() return if $user is null?

A Empty string

B An error

C null

D Boolean false

If $user is null, the null safe operator returns null instead of causing an error.

Can you chain multiple null safe operators in PHP?

A Yes, to safely access nested properties or methods

B No, only one null safe operator is allowed

C Only with arrays

D Only with static methods

You can chain null safe operators to safely access nested properties or methods.

Which PHP version introduced the null safe operator?

A PHP 7.4

B PHP 8.2

C PHP 5.6

D PHP 8.0

The null safe operator was introduced in PHP 8.0.

What happens if you use -> instead of ?-> on a null object?

A Returns null

B A fatal error occurs

C Returns false

D Automatically creates the object

Using -> on a null object causes a fatal error, unlike ?-> which safely returns null.

Explain how the null safe operator works in PHP and why it is useful.

Think about how it helps when you try to access something on an object that might not exist.

Describe a situation where chaining null safe operators would be helpful.

Imagine you want to get a deeply nested property but some parts might be missing.

Practice

1. What does the null safe operator ?-> do in PHP?

easy

A. It allows accessing a property or method only if the object is not null, otherwise returns null.

B. It throws an error if the object is null when accessing a property or method.

C. It converts null values to empty strings automatically.

D. It forces the object to be non-null before accessing properties or methods.

Solution

1. Step 1: Understand the null safe operator purpose

   The null safe operator ?-> is used to safely access properties or methods of an object that might be null.

2. Step 2: Behavior when object is null

   If the object is null, instead of throwing an error, it returns null immediately without calling the property or method.

3. Final Answer:

   It allows accessing a property or method only if the object is not null, otherwise returns null. -> Option A

4. Quick Check:

   Null safe operator = safe access or null return [OK]

Hint: Think: safe access without errors returns null if null [OK]

Common Mistakes:

• Assuming it throws an error on null
• Confusing it with the regular object operator ->
• Thinking it converts null to empty string

2. Which of the following is the correct syntax to use the null safe operator in PHP?

easy

A. $user.?getName();

B. $user->?getName();

C. $user?->getName();

D. $user?getName();

Solution

1. Step 1: Recall the correct null safe operator syntax

   The null safe operator is written as ?-> immediately after the variable name.

2. Step 2: Check each option

   $user?->getName(); uses ?-> correctly. Options B, C, and D have incorrect placements or missing characters.

3. Final Answer:

   $user?->getName(); -> Option C

4. Quick Check:

   Correct syntax = ?-> [OK]

Hint: Remember: question mark before arrow ?-> is correct [OK]

Common Mistakes:

• Placing ? after -> or in wrong position
• Using only ? without ->
• Confusing with ternary operator syntax

3. What will be the output of the following PHP code?

$user = null;
echo $user?->getName() ?? 'Guest';

medium

A. Empty string

B. Error: Call to a member function getName() on null

C. null

D. Guest

Solution

1. Step 1: Evaluate the null safe operator usage

   $user is null, so $user?->getName() returns null safely without error.

2. Step 2: Apply null coalescing operator

   The expression uses ?? 'Guest', so since left side is null, it returns 'Guest'.

3. Final Answer:

   Guest -> Option D

4. Quick Check:

   Null safe + null coalescing = fallback value [OK]

Hint: Null safe returns null, ?? provides fallback [OK]

Common Mistakes:

• Expecting an error when calling method on null
• Confusing null safe with regular -> operator
• Ignoring the null coalescing fallback

4. Identify the error in the following PHP code using the null safe operator:

$order = null;
echo $order?->getItem()->getName();

medium

A. No error, code runs fine and outputs null.

B. Error because getItem() is called on null without null safe operator.

C. Syntax error due to missing semicolon.

D. Error because null safe operator cannot be chained.

Solution

1. Step 1: Analyze the null safe operator chaining

   The first null safe operator ?-> safely calls getItem() on $order which is null, so it returns null.

2. Step 2: Check the next method call

   Then getName() is called on the result of getItem() without null safe operator, causing an error because it's called on null.

3. Final Answer:

   Error because getItem() is called on null without null safe operator. -> Option B

4. Quick Check:

   Chained calls need ?-> on each nullable step [OK]

Hint: Use ?-> before every nullable method call in chain [OK]

Common Mistakes:

• Assuming one ?-> covers all chained calls
• Ignoring that getName() is called on null
• Thinking null safe operator fixes all errors automatically

5. Given the following PHP code, what will be the output?

class Profile {
    public ?string $nickname = null;
}

class User {
    public ?Profile $profile = null;
}

$user = new User();
$user->profile = new Profile();
$user->profile->nickname = null;

echo $user?->profile?->nickname ?? 'No nickname';

hard

A. No nickname

B. null

C. Error: Cannot access property on null

D. Empty string

Solution

1. Step 1: Trace object properties and null safe operator

   $user is an object, $user->profile is an object, but $user->profile->nickname is null.

2. Step 2: Evaluate null safe operator and null coalescing

   The expression $user?->profile?->nickname safely returns null because nickname is null. Then ?? 'No nickname' returns 'No nickname'.

3. Final Answer:

   No nickname -> Option A

4. Quick Check:

   Null safe returns null, ?? fallback used [OK]

Hint: Null safe returns null, ?? gives fallback string [OK]

Common Mistakes:

• Expecting null output instead of fallback string
• Thinking null safe operator throws error on null property
• Confusing null and empty string values