Understanding the PHP Double Question Mark (??) Operator

TL;DR

The PHP double question mark operator is a null coalescing operator which basically means if the value in a variable is null a default value can be assigned.

Example:

$variable = $var ?? 'default value';

• If $var is set and not null, $variable will be assigned $var.
• If $var is not set or is null, $variable will be assigned 'default value'.

In the rest of this blog post, we’ll explore what the double question mark operator does, and how you can use it effectively with some practical examples.

Outline:

1. Introduction
2. What Does the PHP Double Question Mark (??) Operator Do?
3. Examples of the Null Coalescing Operator in Action
   • Example 1: Handling Undefined Variables
   • Example 2: Simplifying Ternary Operations
   • Example 3: Working with Arrays
4. Why Use the Double Question Mark Operator?
5. Conclusion

1. Introduction

In many programming languages, including PHP, developers frequently need to check if a variable is set or has a value before using it in their code. Traditionally, this often involved using isset() or writing long conditional checks. However, with the introduction of the double question mark (??) operator in PHP 7, developers can now write shorter, cleaner, and more readable code. This blog will help you understand the purpose of this operator, how it works, and where you can apply it in your PHP projects.

2. What Does the PHP Double Question Mark (??) Operator Do?

The null coalescing operator (??) is used to return the first operand (on the left) if it exists and is not null; otherwise, it returns the second operand (on the right). In simple terms, it checks if the left-hand side is set and not null and, if it is, it returns that value. If not, it returns the default value specified on the right-hand side.

This operator is primarily a shorthand for isset() combined with a ternary operator.

Syntax:

$variable = $var ?? 'default value';

• If $var is set and not null, $variable will be assigned $var.
• If $var is not set or is null, $variable will be assigned 'default value'.

3. Examples of the Null Coalescing Operator in Action

Example 1: Handling Undefined Variables

Let’s say you have a variable $name that may or may not be defined. With the null coalescing operator, you can provide a default value if $name is not set:

$name = $_GET['name'] ?? 'Guest';
echo "Hello, $name!";

Explanation:

• If the $_GET['name'] variable is set and not null, it will be used as the $name.
• If it’s not set or is null, the string 'Guest' will be used as the default value.

This is much cleaner and shorter than writing:

$name = isset($_GET['name']) ? $_GET['name'] : 'Guest';

Example 2: Simplifying Ternary Operations

Before PHP 7, handling possible null values or undefined variables often involved the ternary operator, like this:

$age = isset($user['age']) ? $user['age'] : 'Unknown';

With the double question mark operator, this can be simplified:

$age = $user['age'] ?? 'Unknown';

If $user['age'] is not set, 'Unknown' will be assigned to $age.

Example 3: Working with Arrays

You can also use the double question mark operator when working with associative arrays to handle cases where a key might not exist:

$user = [
    'name' => 'John Doe',
    'email' => '[email protected]'
];

$phone = $user['phone'] ?? 'No phone number provided';
echo $phone; // Output: No phone number provided

Here, if the phone key does not exist in the $user array, the default message 'No phone number provided' is returned.

4. Why Use the Double Question Mark Operator?

The double question mark (??) operator is a valuable addition to PHP for several reasons:

• Simplifies Code: It reduces the need for repetitive isset() checks and ternary conditions, making your code shorter and easier to read.

• Improves Readability: It allows for concise expressions where default values are needed, particularly when working with user inputs, form data, or dynamic arrays.

• Handles Null Values Gracefully: The null coalescing operator doesn’t throw an error if a variable is undefined. Instead, it gracefully falls back to a default value, which can help avoid undefined variable or index not found warnings.

5. Conclusion

The double question mark (??) operator in PHP is a simple yet powerful tool for handling undefined or null variables. It allows developers to write cleaner and more concise code, which improves both readability and maintainability. Whether you’re dealing with user inputs, array keys, or any potentially null values, the null coalescing operator is an effective solution.

By embracing this operator, you can streamline your conditional checks and reduce boilerplate code, allowing for a smoother development experience. Start using it in your PHP projects today to handle defaults in a more elegant way!