Null safe operator in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely access the property without error if the object is null.

PHP

$length = $obj[1]->length;

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

A->

B->?

C::

D?->

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' causes an error if the object is null.

Using '::' is for static access, not for object properties.

Using '->?' is not valid syntax.

The null safe operator in PHP is '?->' which allows safe access to properties or methods even if the object is null.

2fill in blank

medium

Complete the code to safely call the method if the object is not null.

PHP

$result = $user[1]->getName();

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

A->

B::

C?->

D->?

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' causes fatal error if $user is null.

Using '::' is for static methods, not instance methods.

Using '->?' is invalid syntax.

Using '?->' calls the method only if $user is not null, otherwise returns null safely.

3fill in blank

hard

Fix the error in safely accessing the nested property.

PHP

$city = $person[1]->address[2]->city;

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

A?->

B->

C::

D->?

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' causes errors if any intermediate property is null.

Using '::' is incorrect for instance property access.

Using '->?' is invalid syntax.

Use '?->' for both property accesses to safely handle null values in the chain.

4fill in blank

hard

Fill both blanks to safely access the nested method call.

PHP

$result = $order[1]->getCustomer()[2]->getName();

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

A?->

B->

C::

D->?

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' causes errors if any method returns null.

Using '::' is for static methods only.

Using '->?' is invalid syntax.

Both method calls use '?->' to safely handle null values in the chain.

5fill in blank

hard

Fill all three blanks to safely access a deeply nested property.

PHP

$value = $config[1]->settings[2]->display[3]->theme;

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

A?->

B->

C::

D->?

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' causes fatal errors if any property is null.

Using '::' is invalid for instance properties.

Using '->?' is not valid syntax.

All property accesses use the null safe operator '?->' to avoid errors if any part is null.

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