PHP Single vs Double Question Mark: Difference & Code Examples

Difference between single vs double question mark in PHP

The single question mark is used for a ternary operator for simple if / then statements, whereas the double is used for null coalescing. The double question mark will return the first non-null value. You can run multiple instances of the double question mark in a single statement if there’s a chance you have multiple null values. Now, let’s discuss PHP single double question mark starting from the code example.

Single vs Double Question Mark PHP Code Example

// 
/// Single Question Mark Ternary Example
//
$iLikeCats = false;

echo $iLikeCats ? 'Yes, cats are awesome!' : 'No way, I can't stand cats!';
// output: 'No way, I can't stand cats!';


/// Double Question Mark Null Coalescing Example
//

$userName = null;
$defaultName = 'Guest';

$displayName = $userName ?? $defaultName;

echo $displayName; // Output: Guest

This article aims to provide a clear and comprehensive understanding of the differences between PHP single vs double question marks. Through real code examples, we will demonstrate the use of both operators and discuss their respective syntax, use cases, and best practices. 

We will also compare the two operators(PHP single vs double question mark), highlighting their syntax differences, performance implications, and when to choose one over the other. Additionally, we will offer tips for using null coalescing operators effectively, including combining them with other PHP features and utilizing the null coalescing assignment operator introduced in PHP 7.4.

Article Highlights

• The ternary operator (single question mark) is used for simple if-else statements based on a condition, whereas the null coalescing operator (double question mark) is designed to handle null values more efficiently by returning the first non-null value in a series of expressions.
• The ternary operator has the syntax (condition)? (value_if_true) : (value_if_false) while the null coalescing operator has the syntax (expression1) ?? (expression2) ?? ….
• The null coalescing operator can be more efficient in certain situations, as it stops evaluating expressions once it encounters a non-null value, avoiding unnecessary computation.
• The null coalescing operator can be combined with PHP functions like isset() and empty() for more robust and efficient code.
• With PHP 7.4+, the null coalescing assignment operator (??=) can streamline code further and improve readability.
• Choosing the appropriate operator for a specific use case is essential for writing clean, efficient, and maintainable PHP code.
• Practicing and mastering both the ternary and null coalescing operators can significantly improve your PHP programming skills and enhance the quality of your projects.

Table of Contents

In this article, we will cover the following topics.

1. A brief explanation of PHP’s null coalescing operators.
2. Importance of understanding the difference between a single and double question mark.
3. Single Question Mark: The Ternary Operator.
4. Double Question Mark: The Null Coalescing Operator.
5. Comparison: Ternary Operator vs Null Coalescing Operator.
6. Tips for Using Null Coalescing Operators Effectively.
7. Using PHP single vs double question Summary.

A brief explanation of PHP’s null coalescing operators

PHP’s null coalescing operators are a set of shorthand notations used to simplify certain expressions and improve code readability. These operators include the single question mark (ternary operator) and the double question mark (null coalescing operator). 

The ternary operator is used to create concise conditional expressions, while the null coalescing operator helps developers provide fallback values for potentially null variables. Each operator has a distinct function, and understanding their differences is crucial for writing clean and efficient code in PHP.

PHP’s null coalescing operators are powerful tools that help developers write more concise and efficient code when dealing with conditional expressions and null values. The ternary operator creates compact if-else statements, while the null coalescing operator provides an elegant way to handle null values and specify fallback options. Understanding the differences between these two operators is essential for writing clean, efficient, and maintainable PHP code.

Importance of understanding the difference between PHP single vs double question mark

Understanding the difference between the single and double question mark operators is essential for PHP developers, as each operator serves a different purpose and offers unique benefits. Using these operators correctly can lead to cleaner, more efficient code and helps to prevent errors or unexpected behavior. Furthermore, knowing the appropriate situations in which to use each operator can improve the overall quality of your code, making it easier to read, understand, and maintain.

Single Question Mark: The Ternary Operator

Definition and syntax

The ternary or conditional operator is a concise way to write simple if-else statements in PHP. A three-operand operator takes a condition, a value to be returned if the condition is true, and another value to be returned if the condition is false. 

The syntax for the ternary operator is:

$result = (condition) ? (value_if_true) : (value_if_false);

Real code example: simple ternary operation

Here’s an example of a simple ternary operation to determine if a user is an adult or a minor based on their age:

$userAge = 18;
$ageStatus = ($userAge >= 18) ? 'adult' : 'minor';

echo $ageStatus; // Output: adult

In this example, the condition is $userAge >= 18. If the condition is true, the variable $ageStatus is assigned the value ‘adult’; otherwise, it’s assigned the value ‘minor.’

Real code example: nested ternary operations

Ternary operators can also be nested within each other to handle more complex scenarios. However, this can lead to decreased readability if not used carefully. Here’s an example of a nested ternary operation to determine a student’s grade based on their score:

$score = 85;
$grade = ($score >= 90) ? 'A' : (($score >= 80) ? 'B' : 'C');

echo $grade; // Output: B

In the above code example, the outer ternary operator checks if the score is greater than or equal to 90. It assigns the value ‘A’ to the variable $grade if it is. If not, the inner ternary operator checks if the score is greater than or equal to 80. If it is, it assigns the value ‘B,’ and if not, it assigns the value ‘C.’

Use cases and best practices

The ternary operator is best suited for simple conditional expressions where an if-else statement would be too lengthy. It can lead to more concise and readable code when used appropriately.

However, there are some best practices to follow when using the ternary operator:

1. Avoid nesting ternary operators: Nested ternary operations can quickly become difficult to read and maintain. In cases where multiple conditions need to be checked, consider using regular if-else statements or switch statements instead.
2. Keep conditions simple: Ensure that the conditions used in ternary operators are straightforward and easy to understand. Complex conditions may make the code harder to read.
3. Use parentheses for clarity: Although not always required, using parentheses to group the operands can improve code readability, especially in more complex expressions.

By adhering to these best practices, you can use the ternary operator effectively while maintaining code readability and maintainability.

Double Question Mark: The Null Coalescing Operator

Definition and syntax

The null coalescing operator, introduced in PHP 7, is a shorthand way to return the first non-null value in a list of expressions. It evaluates expressions from left to right and returns the first non-null value encountered. If all expressions are null, it returns the last expression. 

The syntax for the null coalescing operator is:

$result = (expression1) ?? (expression2) ?? ...;

Real code example: basic null coalescing operation

In this example, we use the null coalescing operator to assign a default display name if the $userName variable is null:

$userName = null;
$defaultName = 'Guest';

$displayName = $userName ?? $defaultName;

echo $displayName; // Output: Guest

In this case, since $userName is null, the null coalescing operator returns the value of $defaultName, which is ‘Guest.’

Real code example: chaining null coalescing operations

The null coalescing operator can be chained to handle multiple fallback options. In this example, we check for the availability of primary and secondary email addresses and provide a default email address if both are null:

$primaryEmail = null;
$secondaryEmail = 'john@example.com';
$defaultEmail = 'no-email@example.com';

$email = $primaryEmail ?? $secondaryEmail ?? $defaultEmail;

echo $email; // Output: john@example.com

In this scenario, since $primaryEmail is null, the null coalescing operator moves to the next expression, $secondaryEmail, which is not null, so it returns its value, ‘john@example.com’.

Use cases and best practices

The null coalescing operator is ideal for scenarios where you need to provide a fallback value for a potentially null variable. It leads to cleaner and more readable code, especially when dealing with multiple fallback options. 

Here are some best practices to follow when using the null coalescing operator:

1. Prioritize readability: While the null coalescing operator can make your code more concise, ensure that it remains readable and maintainable. Use descriptive variable names and avoid chaining too many null coalescing operators together, as it can make the code difficult to understand.
2. Combine with other PHP functions: To create more robust and efficient code, you can combine the null coalescing operator with other PHP functions like isset() and empty().
3. Know your PHP version: The null coalescing operator is only available in PHP 7 and later versions. Be aware of your target environment’s PHP version to avoid compatibility issues.

By following these best practices, you can effectively use the null coalescing operator to handle null values and provide fallback values for your variables while maintaining code readability and maintainability.

Comparison: Ternary Operator vs Null Coalescing Operator

Syntax differences

The ternary operator (single question mark) and the null coalescing operator (double question mark) have distinct syntaxes to serve their specific purposes.

Ternary Operator

$result = (condition) ? (value_if_true) : (value_if_false);

The ternary operator takes a condition, a value to return if the condition is true, and another value to return if the condition is false.

Null Coalescing Operator

$result = (expression1) ?? (expression2) ?? ...;

The null coalescing operator evaluates a series of expressions from left to right and returns the first non-null value encountered.

Performance implications

The ternary operator and null coalescing operator both have good performance characteristics. However, the null coalescing operator can be more efficient in certain situations, particularly when dealing with null values. Since the null coalescing operator stops evaluating expressions once it encounters a non-null value, it avoids unnecessary computation, leading to better performance in some cases.

Real code example: ternary operator vs null coalescing operator in similar situations

Here’s an example of using both the ternary operator and the null coalescing operator in similar situations:

// Using the ternary operator
$userName = isset($_GET['name']) ? $_GET['name'] : 'Guest';
echo $userName;

// Using the null coalescing operator
$userName = $_GET['name'] ?? 'Guest';
echo $userName;

Both examples achieve the same goal of assigning a default value to the $userName variable if it is not set. However, the null coalescing operator provides a more concise and readable solution.

When to choose one over the other

The choice between the ternary operator and the null coalescing operator depends on the specific use case:

1. Ternary Operator: Choose the ternary operator when you need to create concise conditional expressions based on a condition not only limited to checking for null values. It is best suited for simple if-else statements where the condition is not explicitly related to the presence or absence of a null value.

2. Null Coalescing Operator: Choose the null coalescing operator when providing a fallback value for a potentially null variable. It is ideal for situations where you need to handle multiple fallback options and ensure that a default value is provided when all other options are null.

By understanding the differences between these two operators and their respective use cases, you can make informed decisions on which operator to use in different situations, leading to cleaner, more efficient, and maintainable PHP code.

Tips for Using Null Coalescing Operators Effectively

Readability and maintainability

While null coalescing operators can help make your code more concise, it’s essential to ensure that your code remains readable and maintainable. 

To achieve this, follow these guidelines:

1. Use descriptive variable names: Choose variable names that convey their purpose and make your code easier to understand.
2. Avoid excessive chaining: While chaining null coalescing operators can be useful in certain situations, avoid chaining too many of them together. Excessive chaining can make your code difficult to read and understand.
3. Be mindful of operator precedence: When combining null coalescing operators with other operators, be aware of the order of operations to prevent unexpected behavior. Use parentheses to group expressions when necessary to improve clarity.

Combining with other PHP features (e.g., isset(), empty())

You can combine the null coalescing operator with other PHP functions to create more robust and efficient code. For example:

Using isset()

$userId = $_GET['id'] ?? null;

if (isset($userId)) {
    // Process the user ID
}

In this example, the null coalescing operator provides a default null value for $userId if it’s not set. Then, isset() checks if $userId has a value before processing it.

Using empty()

$username = $_GET['username'] ?? '';

if (!empty($username)) {
    // Process the username
}

Here, the null coalescing operator assigns an empty string as the default value for $username. The empty() function then checks if $username has a non-empty value before processing it.

Using the null coalescing assignment operator (PHP 7.4+)

Starting with PHP 7.4, you can use the null coalescing assignment operator (??=) to simplify your code even further. The ??= operator assigns the value of the right-hand operand to the left-hand operand only if the left-hand operand is null. 

It can be used as a shorthand for the following pattern:

// Before PHP 7.4
$price = $price ?? 10;

// With PHP 7.4+
$price ??= 10;

In both examples, the $price is assigned the value 10 only if it’s currently null. The null coalescing assignment operator makes the code more concise and easier to read.

You can create clean, efficient, and maintainable code by following these tips and combining null coalescing operators with other PHP features. Additionally, using the null coalescing assignment operator in PHP 7.4+ can further streamline your code, leading to improved readability and a more elegant programming style.

Using PHP single vs double question mark Summary

This article explains the difference between PHP single vs double question mark. This article also compares the ternary operator and the null coalescing operator in PHP, highlighting their syntax, use cases, and best practices. It emphasizes the importance of choosing the right operator for a specific task and provides tips for effectively using the null coalescing operator.

By understanding the differences between these two operators and practicing their use, developers can improve their PHP programming skills and create more efficient, maintainable code.

1. Ternary Operator (single question mark): This operator creates concise if-else statements based on a condition. It takes a condition, a value to return if the condition is true, and another value to return if the condition is false.
2. Null Coalescing Operator (double question mark): This operator is designed to handle null values more efficiently by returning the first non-null value in a series of expressions. It evaluates each expression from left to right and returns the first non-null value encountered.

Emphasizing the importance of choosing the right operator for the task

Choosing the appropriate operator for your specific use case is essential for writing clean, efficient, and maintainable PHP code. Use the ternary operator when you need a concise if-else statement based on a condition, and opt for the null coalescing operator when you want to handle null values and provide fallback options.

Encouragement to explore further and practice using both operators

Understanding and mastering the ternary and null coalescing operators can significantly improve your PHP programming skills. To gain expertise using these operators, explore different real-world scenarios, experiment with various use cases, and practice writing code using both operators. 

As you become more proficient, you can write more elegant, efficient, and maintainable PHP code, ultimately enhancing the quality of your projects and increasing your effectiveness as a developer.

PHP Object-Oriented Programming Learning Path

This article is part of our series on learning Object-oriented programming with PHP. It introduces some concepts, best practices and strategies to help you level up your skills. This is a great intro to growing into a successful programmer.

• Object-Oriented PHP Programming
• PHP Classes
• PHP Abstract Classes
• PHP Interfaces
• Data Structures
• Design Patterns
• Dependency Injection
• Single vs Double Question Marks

Learn the Fundamentals of Good Web Development

Please take a moment and sign up for our free email course on the fundamentals of good web development. Every week is packed with a roundup of articles on our site and from around the web, where we go deep into developing exceptional web applications. We have meetups, code reviews, slack chats, and more.

Click here to get started